Removal of volatile organic compounds by chemical filters significantly inhibited the development of atopic dermatitis symptoms in mice: potential implications for air-conditioning systems in healthcare environments
Chiharu Ohira, Kengo Tomita, Yukiko Ota, Keiichi Yano, Mona Amano, Mao Kaneki, Atsushi Yamada, Riku Usui, Yuzo Nagai, Masaki Nagane, Satoshi Takagi, Tomoki Fukuyama
TL;DR
Removing volatile organic compounds (VOCs) in healthcare environments may help prevent or reduce atopic dermatitis symptoms in mice.
Contribution
This study demonstrates that VOC removal using chemical filters can inhibit AD development in a mouse model and in real clinical settings.
Findings
VOC exposure worsened AD symptoms and keratinocyte inflammation in mice.
Chemical filters effectively reduced VOC levels and suppressed AD development.
VOC removal had limited effects on systemic immunological markers.
Abstract
Volatile organic compounds (VOCs) are increasingly implicated in systemic diseases, but their contribution to skin disorders such as atopic dermatitis (AD) remains unclear. This study assessed VOC concentrations in medical environments, their effects on AD development, and the efficacy of VOC removal using chemical filters. Total VOC levels were monitored in 3 types of veterinary hospitals. AD-like lesions were induced in female NC/Nga mice by repeated dermal application of toluene diisocyanate or house dust mite ointment, with or without topical exposure to a VOC mixture (10 μg/ml). Clinical parameters, including dermatitis scores, transepidermal water loss, and skin thickness, were measured weekly, and immunological and histological analyses were performed. VOC monitoring revealed that 1 hospital exhibited concentrations exceeding 400 μg/m³. In the mouse model, direct VOC exposure…
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Fig. 7| Untreated | AD control | AD VOC | |
|---|---|---|---|
|
| |||
| Epidermis | |||
| Parakeratosis | 0.00 ± 0.00 | 1.00 ± 0.00 | 1.57 ± 0.20 |
| Hyperplasia in keratinized layer | 0.00 ± 0.00 | 0.88 ± 0.23 | 1.14 ± 0.14 |
| Hyperplasia in non-keratinized layer | 0.00 ± 0.00 | 1.88 ± 0.13 | 2.00 ± 0.00 |
| Inflammatory cell infiltration | 0.00 ± 0.00 | 1.38 ± 0.26 | 2.29 ± 0.18 |
| Crust | 0.00 ± 0.00 | 1.50 ± 0.27 | 2.43 ± 0.20 |
| Ulceration | 0.00 ± 0.00 | 1.00 ± 0.46 | 2.00 ± 0.31 |
| Dermis | |||
| Inflammatory cell infiltration | 0.00 ± 0.00 | 2.00 ± 0.19 | 2.43 ± 0.20 |
|
| |||
| Epidermis | |||
| Parakeratosis | 0.00 ± 0.00 | 1.38 ± 0.18 | 1.86 ± 0.26 |
| Hyperplasia in keratinized layer | 0.00 ± 0.00 | 1.00 ± 0.00 | 2.00 ± 0.22 |
| Hyperplasia in non-keratinized layer | 0.00 ± 0.00 | 2.00 ± 0.00 | 2.00 ± 0.00 |
| Inflammatory cell infiltration | 0.00 ± 0.00 | 1.38 ± 0.26 | 2.43 ± 0.20 |
| Crust | 0.00 ± 0.00 | 1.88 ± 0.23 | 2.14 ± 0.26 |
| Ulceration | 0.00 ± 0.00 | 0.38 ± 0.18 | 0.14 ± 0.14 |
| Dermis | |||
| Inflammatory cell infiltration | 0.00 ± 0.00 | 1.75 ± 0.16 | 2.43 ± 0.20 |
| Room-air | CF-air | |
|---|---|---|
|
| ||
| Epidermis | ||
| Hyperplasia in keratinized layer | 2.13 ± 0.13 | 1.22 ± 0.15 |
| Hyperplasia in non-keratinized layer | 2.13 ± 0.13 | 1.78 ± 0.15 |
| Ulceration | 2.88 ± 0.13 | 0.56 ± 0.34 |
| Dermis | ||
| Inflammatory cell infiltration | 3.00 ± 0.00 | 1.67 ± 0.24 |
|
| ||
| Epidermis | ||
| Hyperplasia in keratinized layer | 2.50 ± 0.19 | 1.22 ± 0.28 |
| Hyperplasia in non-keratinized layer | 2.38 ± 0.18 | 1.56 ± 0.18 |
| Ulceration | 1.50 ± 0.19 | 0.78 ± 0.28 |
| Dermis | ||
| Inflammatory cell infiltration | 2.13 ± 0.13 | 1.44 ± 0.24 |
- —Shimizu Corporation, 3-4-17 Etchujima, Koto-ku, Tokyo 135-8530, Japan
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Taxonomy
TopicsAllergic Rhinitis and Sensitization · Dermatology and Skin Diseases · Asthma and respiratory diseases
The composition of air pollution includes a mixture of substances such as particulate matter, nitrogen oxides, ozone, volatile organic compounds (VOCs), and polycyclic aromatic hydrocarbons (PAHs). Over the years, the adverse health effects of air pollution have become a serious global concern (Brunekreef et al. 2021; Sawada et al. 2022). Air pollutants have been associated with major causes of mortality, including cardiovascular disease, stroke, respiratory diseases, and cancer (Brunekreef et al. 2021; Sawada et al. 2022). In addition, previous studies have reported that air pollution contributes to central nervous system diseases by inducing neuroinflammation (Block and Calderon-Garciduenas 2009). Because people spend more than 90% of their time indoors, there is increasing interest in the relationship between indoor air quality (IAQ) and human health. Our group previously investigated the safety of ozone gas, which is used as a disinfectant in hospitals and homes, in patients with respiratory diseases (Ohira et al. 2023). Although the safety standard for ozone gas is set at 0.1 ppm in many countries, our study revealed that exposure to ozone at this concentration exacerbated symptoms in an asthma mouse model. This finding suggests that the safety standard for ozone exposure in respiratory diseases should be reconsidered. IAQ can be influenced by various human activities, and one of the major pollutants is VOCs. VOCs are emitted from a wide range of sources, including solvents, cleaning agents, construction materials, and personal or recreational products, and they consist of diverse harmful chemicals. Indoor VOC concentrations are generally 2 to 5 times higher than outdoor levels, and during or after the use of VOC-emitting materials, individuals may be exposed to extremely high concentrations. Numerous studies have reported the incidence of diseases and adverse health effects associated with VOC exposure. Bönisch et al. (2012) demonstrated that polyvinyl chloride (PVC) emitted from flooring materials promotes the production of Th2-type cytokines such as interleukin (IL)-4, IL-5, and IL-13, thereby enhancing immune responses and aggravating airway inflammation. An epidemiological study by Iwata et al. (2024) reported that exposure to tatami mats may increase the risk of childhood asthma.
Several studies have measured VOC concentrations in actual indoor environments. Lin et al. (2021) assessed VOC levels in different work areas of hotels by attaching samplers to employees’ clothing to evaluate exposure during routine work activities. Their study reported that VOCs such as alkanes, formaldehyde, and BTEX compounds were emitted from sources including detergents, fabric softeners, and bleach, and that the levels varied significantly depending on the type of work performed.
Formaldehyde, a known carcinogen, has regulated threshold values in many countries. However, concentrations exceeding these limits have been detected in commercial facilities, hotels, and residential buildings. Indoor VOC concentrations, including but not limited to formaldehyde, vary considerably and cannot be generalized as consistently high (Wu et al. 2011; Nirlo et al. 2014). In medical settings, VOCs have been investigated in relation to disinfectant use, whereas in industrial facilities, VOC emissions have been examined during manufacturing processes. These studies indicate that the types and levels of VOC exposure differ according to occupation, highlighting the need for task-specific mitigation strategies (Su et al. 2018; Zhang et al. 2024). Nonetheless, effective methods to reduce indoor VOC concentrations have not yet been fully established.
Based on the above epidemiological studies and research findings, it has become clear that individuals are exposed to VOCs in daily life and that VOC exposure increases disease incidence and exacerbates symptoms. However, only a few studies have examined VOC exposure on the skin, which is in frequent contact with air. In this study, we conducted a survey of IAQ in medical settings and investigated the effects of VOCs on the onset of atopic dermatitis (AD), as well as potential strategies for mitigation. Furthermore, we examined the effects of VOC exposure on skin disorders through both in vitro and in vivo experiments.
Materials and methods
Monitoring VOCs in veterinary hospitals
The concentrations of total VOCs (TVOCs) and their compositions were monitored in 3 different types of veterinary hospitals in Japan. The characteristics of the air intake and exhaust systems are summarized in Fig. 1A. Air samples were collected from operating rooms, treatment rooms, waiting rooms, and outdoor air at each hospital using Tenax-GR tubes (GL Sciences Inc., Tokyo, Japan) at a flow rate of 0.5 l/min for 20 min (10 l total). TVOC concentrations and compositions were analyzed by thermal desorption (TD) gas chromatography (GC) with flame ionization detection (FID). The analysis was performed using a TD analyzer (TD-20, Shimadzu Corporation, Kyoto, Japan) coupled with a capillary GC and an FID (GC-2010 Plus, Shimadzu Corporation, Kyoto, Japan), according to a previous report (Mizuno et al. 2023). For the circle chart, the top 20 species were grouped into n-alkanes, aromatics, aldehydes, siloxanes, terpenes, glycol ethers, chlorinated compounds, others, and unknown.
The concentrations of TVOCs in several rooms were monitored in 3 different types of veterinary hospitals in Japan. The provisional target value established by the Ministry of Health, Labour and Welfare (400 μg/m3) is indicated by a dotted line. Characteristics of the air intake and exhaust systems are also summarized (A). The top 20 VOC species, grouped into n-alkanes, aromatics, aldehydes, siloxanes, terpenes, glycol ethers, chlorinated compounds, others, and unknowns, are shown (B to D). TVOCs, total volatile organic compounds; MHLW, Ministry of Health, Labour and Welfare.
Direct and indirect cytotoxicity and inflammatory responses of VOCs in human epidermal keratinocytes
The human epidermal keratinocyte cell line (HaCaT) was purchased from CLS Cell Lines Service GmbH (Eppelheim, Germany) and cultured in Dulbecco’s Modified Eagle’s Medium (DMEM; FUJIFILM Wako Pure Chemical Corporation, Osaka, Japan) supplemented with 10% fetal calf serum (Sigma-Aldrich Co. LLC., Tokyo, Japan) and penicillin–streptomycin (FUJIFILM Wako Pure Chemical Corporation). Various concentrations (3.125 to 100 μg/ml) of a standard VOC solution (48 Component Indoor Air Standard, 40353-U, Sigma-Aldrich Co. LLC) were added to HaCaT cells (1 × 10^4^ cells) seeded in 96-well plates. After 24 h of incubation (37 °C, 5% CO_2_), cell viability was assessed using a lactate dehydrogenase release assay (Cytotoxicity LDH Assay Kit-WST, DOJINDO LABORATORIES, Kumamoto, Japan). The concentrations of IL-8 and thymus and activation-regulated chemokine (TARC) in supernatants without cytotoxicity (5 and 10 μg/ml) were quantified by enzyme-linked immunosorbent assay (ELISA; DuoSet ELISA Kit, R&D Systems, Minneapolis, Minnesota, United States). Expression of inflammatory genes, including IL-1β, suppressor of cytokine signaling 3 (SOCS3), and tumor necrosis factor (TNF)-α, was evaluated 24 h after co-incubation with VOCs. In addition, the influence of VOC exposure on cutaneous barrier function was assessed by analyzing the expression of epidermal barrier-related genes, including filaggrin (FLG), filaggrin 2 (FLG2), and loricrin. Total RNA was extracted using the NucleoSpin RNA Kit (TaKaRa Bio Inc., Shiga, Japan) according to the manufacturer’s instructions. Complementary DNA was synthesized from extracted RNA using PrimeScript RT Master Mix (TaKaRa Bio Inc.). Gene expression levels of FLG, FLG2, IL-1β, loricrin, SOCS3, and TNF-α were quantified by real-time PCR using gene-specific primers (TaKaRa Bio Inc.), PowerUp SYBR Green Master Mix (Thermo Fisher Scientific, Kanagawa, Japan), and a CFX Duet Real-Time PCR System (Bio-Rad Laboratories, Inc.). Expression levels were normalized to β-actin, and relative gene expression was calculated using the 2^−ΔΔCt^ method.
To evaluate the adjuvant effects of VOCs, IL-8 and TARC production in the supernatants was measured following either post-stimulation (4 h after stimulation) or co-stimulation with 10 μg/ml TNF-α (R&D Systems). A minimum of 3 independent experiments were performed to confirm the reproducibility of the results.
Animals
Seven-week-old female NC/Nga mice were obtained from Japan SLC, Inc. (Shizuoka, Japan). NC/Nga mice are a well-established model of AD, characterized by spontaneous and inducible eczematous skin lesions, Th2-dominant immune responses, elevated serum IgE levels, and impaired skin barrier function, closely resembling human AD pathology (Matsuda et al. 1997; Suto et al. 1999). Female mice were used to reduce variability associated with aggressive behavior and stress responses observed in male mice and to maintain consistency with previous studies employing this model (Kaneki et al. 2023; Matsuzaka et al. 2024). Mice were housed under controlled conditions (12 h light–dark cycle; temperature, 22 ± 3 °C; humidity, 55% ± 15%) and provided with food and water ad libitum. All animal experiments were conducted in accordance with the Animal Care and Use Program of Azabu University (Approval No. 230509-1).
Exacerbation of AD symptoms by topical exposure to a standard VOC solution
AD-like skin lesions were induced using a commercially available house dust mite ointment (Biostir AD, Biostir Inc., Osaka, Japan) according to the manufacturer’s instructions with minor modifications. Briefly, the dorsal skin and both ear pinnae were shaved and pretreated with 4% sodium dodecyl sulfate solution (FUJIFILM Wako Pure Chemical Corporation) to disrupt the skin barrier. After 24 h, house dust mite ointment (approximately 50 mg/animal) was topically applied to the dorsal skin and ears. This procedure was repeated twice weekly according to the experimental schedule described above. Topical application of a standard VOC solution (10 μg/ml) was performed daily during the experimental period. Transepidermal water loss (TEWL), ear and back skin thickness, and AD scores were monitored weekly. TEWL was measured using a VAPO SCAN (AS-VT100RS, Asch Japan Co., Ltd., Tokyo, Japan). AD severity was scored on a scale of 0 to 4: 0, no symptoms; 1, mild; 2, moderate; 3, severe; and 4, extreme, as described in previous reports (Ando et al. 2023; Kaneki et al. 2023). Back skin, auricular lymph nodes (LNs), and serum samples were collected from each mouse 4 wks after the first sensitization. The collected samples were analyzed for cell differentiation, cytokine release, total IgE levels, histological evaluation, and RNA expression.
Removal of indoor VOCs by chemical filtering system
The chemical filtering (CF) system (professional-use air purifier system, GCO-S01, Fuji Industrial Co., Ltd., Kanagawa, Japan) equipped with activated-carbon filters was used in this study. The system contains high-surface-area activated carbon filters optimized for the physical adsorption of low-molecular-weight VOCs commonly found in indoor environments. The device does not employ plasma discharge, photocatalytic oxidation, or thermal/catalytic decomposition mechanisms. VOC removal therefore occurs through passive adsorption rather than chemical transformation. With respect to selectivity, the CF system also incorporates HEPA filtration for the active removal of particulate matter. Although activated carbon may adsorb limited amounts of certain reactive gases (e.g. ozone) under specific conditions, the system is not engineered for the targeted removal of these co-pollutants. Performance evaluations of the air-conditioning system were conducted in 2 rooms (Room A and Room B) under identical conditions (18.06 m^2^, 2.4 m height, temperature: 27.0 to 30.0 °C, humidity: 70% to 82%) as shown in Fig. 4A. A PVC sheet (1.82 × 4 m, TOLI Corporation, Hyogo, Japan) was placed as a source of VOCs in both rooms. The CF system was operated only in Room A during the first 4 h and then switched to Room B for the last 4 h. The concentrations of TVOCs in both rooms were continuously monitored for 8 h.
Effects of CF on the development of AD symptoms in a mouse model
The experimental design is shown in Fig. 5A. The effects of VOC removal on the development of AD symptoms and inflammatory responses were evaluated in an NC/Nga mouse model of AD. AD symptoms were induced by weekly sensitization and challenge with toluene-2,4-diisocyanate (TDI; CAS No. 584-84-9, FUJIFILM Wako Pure Chemical Corporation) as described in previous reports (Ando et al. 2023; Kaneki et al. 2023). Weekly monitoring of TEWL, ear and back skin thickness, AD scores, and sample collection was performed as in the VOC toxicological study described above. The CF system was operated continuously throughout the 28-d experimental period for the CF-air group, whereas the control group was exposed to untreated room air. The TVOC concentration in the untreated room air was 32.6 μg/m³. Operation of the CF system resulted in approximately 90% removal of VOCs, reducing the TVOC concentration to 3.3 μg/m³ in the CF-air group, as shown in Fig. 5B.
Therapeutic potential of CF on established AD symptoms and the immune system in a mouse model
The experimental design is shown in Fig. 6A. The therapeutic potential of VOC removal on established AD symptoms and the immune system was evaluated in an NC/Nga mouse model of AD. AD symptoms were first induced using the same method as described in the preventive study, and the CF system was operated during the remaining experimental period (21 d) for the CF-air group. Weekly monitoring of TEWL, ear and back skin thickness, AD scores, and sample collection was performed as in the VOC toxicological study described above.
Histopathological assessment of skin samples
A portion of the skin samples was fixed in 10% formalin solution, embedded in paraffin wax, sectioned at a thickness of 5 μm, and stained with hematoxylin and eosin, as described in previous reports (Matsuzaka et al. 2024, 2025). Semi-quantitative histopathological evaluation of parakeratosis, hyperplasia, inflammatory cell infiltration, crust formation, and ulceration in the epidermis and dermis was performed in a blinded fashion using the following grading system: 0, within normal limits; 1, mild; 2, moderate; and 3, severe.
Flow cytometric analysis of LNs
Single-cell suspensions isolated from the auricular LNs were prepared as described previously (Kaneki et al. 2023; Matsuzaka et al. 2024), and the total number of cells was determined using a CellDrop Cell Counting System (DeNovix Inc., Delaware, United States). To avoid nonspecific binding during flow cytometric analysis, 1 × 10^6^ cells were first incubated with 1 µg of mouse Fc Block (Miltenyi Biotec K.K., Tokyo, Japan) prior to incubation with monoclonal antibodies (anti-mouse CD3, anti-mouse CD4, anti-mouse CD11b, anti-mouse CD11c, anti-mouse CD19, anti-mouse MHC class II, DAPI [Miltenyi Biotec K.K.], and anti-mouse IgE [Sony Biotechnology Inc., Tokyo, Japan]). The cells were then washed and analyzed using a BD FACSAria III cell sorter (BD Biosciences, Tokyo, Japan).
Measurement of total serum IgE
Total IgE levels in serum samples were measured using ELISA according to the manufacturer’s protocol (BD Biosciences). Optical density was recorded using a microplate reader (Multiskan SkyHigh, Thermo Fisher Scientific Inc., Kanagawa, Japan).
Cytokine release assay for LNs
Single-cell suspensions of LNs were used to examine cytokine release by T cells as described previously (Kaneki et al. 2023; Matsuzaka et al. 2024, 2025). Briefly, LN single-cell suspensions (5 × 10^5^ cells/well) were incubated with Dynabeads Mouse T-Activator CD3/CD28 (Thermo Fisher Scientific Inc., Kanagawa, Japan) for 24 or 96 h. Subsequently, the levels of IL-4, IL-13, and IL-17 in the supernatants were quantified using ELISA (DuoSet ELISA Kit, R&D Systems).
Gene expression in skin tissues
Gene expression analysis was performed as described previously (Kaneki et al. 2023; Matsuzaka et al. 2024, 2025). Briefly, frozen tissue was homogenized using a bead-beater homogenizer (μT-12, TAITEC CORPORATION, Saitama, Japan), and total RNA was extracted using the NucleoSpin RNA Kit (TaKaRa Bio Inc.). Extracted RNA (500 ng) was reverse transcribed using the PrimeScript RT Master Mix (TaKaRa Bio Inc.). Expression levels of β-actin, FLG2, IL-4, and IL-33 were assessed using gene-specific primers (Takara Bio Inc.), PowerUp SYBR Green Master Mix (Thermo Fisher Scientific Inc.), and a qPCR system (CFX Duet Real-Time PCR System, Bio-Rad Laboratories, Inc.). The expression of each target gene was normalized to β-actin.
Statistical analysis
All in vivo and in vitro data are expressed as the mean ± standard error of the mean (SEM). Statistical analyses were performed using analysis of variance, followed by Dunnett’s multiple comparison test. Statistical significance was evaluated at probability levels of 5% and 1%. Data were analyzed using GraphPad Prism 10.0 (GraphPad Software, San Diego, California, United States).
Results
Monitoring VOCs in veterinary hospitals
The concentrations of TVOCs in Hospital A were maintained at low levels (<100 μg/m^3^), almost comparable to outdoor air, whereas TVOC concentrations in Hospitals B and C exceeded 100 μg/m^3^. The TVOC concentration in Hospital C was nearly 10 times higher than outdoor air and twice as high as the provisional target value established by the Ministry of Health, Labour and Welfare (400 μg/m^3^) (Fig. 1A). The composition of VOCs varied depending on hospital conditions: aromatic hydrocarbons predominated in Hospitals A and B, whereas n-alkanes were the major component in Hospital C (Fig. 1B to D).
Direct and indirect cytotoxicity and inflammatory responses of VOCs in human epidermal keratinocytes
Cytotoxicity induced by direct exposure to VOCs was first examined in the HaCaT. VOC concentrations ≥25 μg/ml reduced cell viability to <50% (Fig. 2B). Inflammatory cytokine production following VOC exposure at noncytotoxic concentrations was subsequently assessed. VOC exposure (0 to 10 μg/ml) significantly increased IL-8 and TARC secretion in a concentration-dependent manner (Fig. 2C). Expression of inflammation-related genes was significantly affected by direct VOC exposure. Treatment with VOCs (10 μg/ml) significantly increased the expression of IL-1β and TNF-α, while significantly decreasing SOCS3 expression (Fig. 2D). In parallel, direct VOC exposure (10 μg/ml) significantly reduced the expression of epidermal barrier-associated genes, including FLG, FLG2, and loricrin (Fig. 2D). To investigate potential adjuvant effects of VOCs in vitro, cells were exposed to VOCs either simultaneously with TNF-α stimulation or 8 h after stimulation. Both IL-8 and TARC production were significantly increased when VOCs were applied 8 h after TNF-α stimulation (Fig. 2E). In contrast, during simultaneous VOC and TNF-α exposure, IL-8 levels were comparable to those of the control group, whereas TARC production was significantly increased (Fig. 2F).
Experimental design of in vitro studies (A). Cytotoxicity induced by direct exposure to VOCs was assessed in HaCaT (B). IL-8 and TARC production after exposure to VOCs at noncytotoxic concentrations (C). Expression of inflammatory- and epidermal barrier-related genes (IL-1β, TNF-α, SOCS3, FLG, FLG2, and loricrin) in HaCaT cells after 24 h of VOC exposure (D). IL-8 and TARC production induced by VOC exposure 8 h after TNF-α stimulation (E). IL-8 and TARC production 24 h after simultaneous VOC exposure with TNF-α stimulation (F). Results are presented as the mean ± SEM (n = 7 per group). P < 0.05, Dunnett’s multiple comparison test vs. 0 μg/ml VOC-treated group. IL, interleukin; TARC, thymus and activation-regulated chemokine; TNF, tumor necrosis factor. Created in BioRender. Fukuyama, T. (2025). https://BioRender.com/t35kifp
Exacerbation of AD symptoms by topical exposure to a standard VOC solution
The indirect effect of VOC exposure on skin inflammation was confirmed in an NC/Nga mouse model of AD sensitized and challenged with house dust mite ointment. Cutaneous barrier function, assessed by TEWL, was not affected by VOC exposure; however, AD symptoms (AD scores) and skin thickness were significantly aggravated compared with the control group (Fig. 3B to E). In AD control mice, characteristic pathological features were observed, including marked epidermal hyperplasia, parakeratosis, inflammatory cell infiltration in the dermis, and occasional crust formation. Topical exposure to VOCs further exacerbated these pathological changes. Compared with the AD control group, VOC-exposed mice exhibited significantly increased epidermal thickness, more extensive inflammatory cell infiltration, and enhanced hyperplasia of the keratinized layer. Crust formation and focal ulceration were also more frequently observed in the VOC-treated group. These changes were reflected in significantly higher histopathological scores for hyperplasia and inflammatory infiltration (Table 1). Representative HE-stained sections from multiple animals per group (n = 6) are shown in Fig. 3F, with corresponding semi-quantitative grading summarized in Tables 1. AD-associated immune hyper-responses were also significantly enhanced by VOC exposure, including expansion of effector helper T cells and increased IL-13 gene expression in the skin compared with the AD control group (Fig. 3G to J).
Experimental design of indirect VOC exposure with skin inflammation confirmed in a mouse model of atopic dermatitis (AD) (A). AD scores (B), skin thickness (C), and cutaneous barrier function measured by TEWL (D) were monitored weekly during the experimental period. Representative back-skin images (E, day 18 of study) are shown for the AD control and AD VOC groups (E). Representative HE-stained sections of dorsal skin collected 4 wks after sensitization and challenge with house dust mite ointment, with or without topical VOC exposure (F). Images are shown for untreated, AD control, and AD + VOC groups. Representative images were selected from multiple biological replicates and illustrate consistent pathological features observed across animals. Scale bar = 100 μm. Semi-quantitative histopathological scores are summarized in Table 1. AD-associated immune hyperresponses were analyzed, including effector helper T cells (G), B cells (H), and IL-13 levels in lymph nodes (I). IL-13 gene expression in the skin was also compared between the AD control and AD VOC groups (J). Results are presented as the mean ± SEM (n = 7 per group). P < 0.05, P < 0.01 (Student’s t-test) vs. AD control group. AD, atopic dermatitis; TEWL, transepidermal water loss; LN, lymph node. Created in BioRender. Fukuyama, T. (2025). https://BioRender.com/0d3n89z
Removal of indoor VOCs by chemical filtering system
To eliminate VOCs from the indoor atmosphere, a specialized CF system based primarily on activated carbon adsorption was developed, and its performance was evaluated under simulated living conditions using a PVC sheet as a continuous VOC source (initial TVOC concentration, 296.9 μg/m³). Operation of the CF system resulted in rapid VOC removal, with more than 60% of TVOCs eliminated within the first 5 min (121.4 μg/m³). Thereafter, TVOC concentrations in Room A, in which the CF system was installed, were maintained below 100 μg/m³ for 4 h (30.1 to 56.3 μg/m³). In contrast, TVOC levels in Room B, which lacked the CF system, remained consistently high during the same period (247.4 to 319.9 μg/m³) (Fig. 4B). After 4 h, the CF system was relocated from Room A to Room B, and TVOC concentrations were monitored for an additional 4 h. Upon initiation of CF system operation in Room B, TVOC concentrations rapidly decreased from 247.4 to 28.4 μg/m³. Conversely, removal of the CF system from Room A resulted in a gradual increase in TVOC levels, reaching 187.7 μg/m³ after 4 h (Fig. 4B). Average TVOC concentrations following CF system initiation are summarized in Fig. 4C.
Performance evaluation of CF system was conducted in 2 rooms (Room A and Room B) under identical conditions with a polyvinyl chloride sheet as the VOC source (A). The CF system was operated only in Room A for the first 4 h, after which the operation was switched to Room B for the following 4 h. The concentrations of TVOCs in both rooms were continuously monitored for 8 h (B). Average levels (n = 2) of TVOCs after CF system initiation are shown (C). Results are presented as the mean ± SEM. CF, chemical filter. Created in BioRender. Fukuyama, T. (2025) https://BioRender.com/ttf8b4x
Effects of CF on the development of AD symptoms in a mouse model
The effects of VOC removal by our developed CF system on AD symptoms and inflammatory responses were evaluated in an NC/Nga mouse model of AD. AD symptoms (AD scores), skin thickness (ear and back), and cutaneous barrier function (TEWL) aggravated by TDI applications were significantly inhibited under CF-air conditions compared with normal room-air conditions (Fig. 5C to G). Amelioration of skin symptoms was confirmed by histopathological evaluations, which showed significant reductions in inflammatory cell infiltration, hyperplasia, and ulceration in the epidermis and/or dermis (Table 2). Representative HE-stained sections from multiple animals per group (n = 7) are shown in Fig. 6A, with corresponding semi-quantitative grading summarized in Tables 2. AD-associated immune hyper-responses were also significantly decreased under CF-air conditions, including reduced numbers of helper T cells and decreased production of IL-4 and IL-17 (Fig. 6B to H). Furthermore, gene expression in skin associated with barrier function, such as Flg2, was significantly increased under CF-air conditions compared with normal room-air conditions (Fig. 6I and J).
Effects of VOC removal by the developed CF system on the development of AD symptoms and inflammatory responses were monitored based on the experimental design (A). Approximately 90% of VOCs were removed from room air by the CF system (B). AD scores (C), ear skin thickness (D), back skin thickness (E), and TEWL (F) were monitored weekly during the experimental period. Representative back-skin images (G, day 28 of study) are shown for the normal room-air and CF-air groups. Results are presented as the mean ± SEM (n = 7 per group). P < 0.05, P < 0.01 (Student’s t-test) vs. normal room-air group. Created in BioRender. Fukuyama, T. (2025). https://BioRender.com/f8w22sr
Representative HE-stained sections of dorsal skin from NC/Nga mice exposed to untreated room air or CF-treated air during TDI-induced AD development (A). Images are representative of multiple animals per group and were selected following blinded histopathological evaluation. Scale bar = 100 μm. Corresponding semi-quantitative histopathological scores are presented in Table 2. AD-associated immune hyper-responses were analyzed, including dendritic cells (B), helper T cells (C), and B cells (D) in LN; total IgE levels in serum (E); and IL-4 (F), IL-13 (G), and IL-17 (H) levels in lymph nodes. Flg2 (I) and IL-33 (J) gene expression in the skin was also compared between the normal room-air and CF-air groups. Results are presented as the mean ± SEM (n = 7 per group). P < 0.05 (Student’s t-test) vs. normal room-air group. Flg, filaggrin.
Therapeutic potential of CF on established AD symptoms and the immune system in a mouse model
The therapeutic potential of VOC removal on established AD symptoms and the immune system was examined in an NC/Nga mouse model of AD. AD symptoms (AD scores), skin thickness (ear and back), and cutaneous barrier function (TEWL) were not influenced by VOC removal (Fig. 7B to E). Enhanced immune responses, including helper T cells, were significantly decreased under CF-air conditions compared with normal room-air conditions; however, the difference was modest, and no changes were observed in cellular functions such as IL-4 production and total IgE levels (Fig. 7F to J). Interestingly, scratching behavior induced by TDI application was significantly reduced under CF-air conditions compared with normal room-air conditions (Fig. 7K).
Experimental design of the therapeutic potential of the CF system on developed AD symptoms and the immune system in a mouse model (A). AD scores (B), ear skin thickness (C), back skin thickness (D), and TEWL (E) were monitored weekly during the experimental period. AD-associated immune hyper-responses were analyzed, including dendritic cells (F), helper T cells (G), B cells (H), and IL-4 levels in lymph nodes (I), as well as total IgE levels in serum (J). Scratching behavior on day 21 was also compared with the normal room-air group (K). Results are presented as the mean ± SEM (n = 7 per group). P < 0.05, P < 0.01 (Student’s t-test) vs. normal room-air group.
Discussion
This study investigated actual indoor VOC levels in veterinary medical facilities and examined their potential effects on the skin. Indoor TVOC levels were measured under different conditions in 3 veterinary hospitals, and both total concentrations and compositional ratios were compared. Because veterinary facilities use more chemicals and medical devices than other types of facilities, it is presumed that higher concentrations of VOCs may accumulate. Hospitals A to C differed in building characteristics, which resulted in distinct TVOC levels. Hospital A, which had higher ceilings, a spacious layout, and a commercial air-conditioning system, showed no accumulation of VOCs, with indoor TVOC levels remaining below 100 μg/m³. In contrast, Hospitals B and C, which had lower ceilings and household air-conditioning systems, exhibited indoor TVOC levels that were 2 to 6 times higher than those in Hospital A. Notably, the TVOC levels in Hospital C exceeded the guideline values established by the Ministry of Health, Labour and Welfare in Japan. The compositional ratios of TVOCs also varied among the hospitals. In Hospitals A and B, aromatic hydrocarbons were predominant, including compounds such as toluene and xylene, which are characterized by stable ring structures. In contrast, Hospital C showed a higher proportion of n-alkanes, such as hexane, which are also chemically stable. These compounds are known to affect the central nervous system following long-term inhalation exposure. However, further investigations are required to clarify the duration and extent of exposure in different types of veterinary facilities.
Deterioration of IAQ adversely affects human health, and numerous studies have reported the effects of inhalation exposure. In addition to respiratory outcomes, increasing attention has been directed toward the impact of inhalation exposure on skin diseases. Although genetic factors contribute to the development of skin diseases, environmental factors also play a significant role. Among these, the association between air pollution and skin disorders has been emphasized. Epidemiological studies have demonstrated that ambient PM_2.5_ exacerbates pediatric allergic skin diseases and eczema (Song et al. 2011). PAHs, which are present in PM_2.5_, can penetrate the skin, promote intracellular reactive oxygen species generation, and enhance inflammatory responses (Krutmann et al. 2014). To investigate the direct effects of VOCs on skin tissue, we exposed HaCaT to VOC standard solutions at various concentrations. High concentrations (25 to 100 μg/ml) reduced cell viability, whereas noncytotoxic concentrations (10 μg/ml) significantly altered inflammatory cytokine production (IL-8, TARC) and associated gene expression (IL-1β, TNFα, SOCS3). These cytokines play key roles in neutrophil recruitment and Th2 cell chemotaxis, respectively, and are known contributors to AD pathogenesis. Notably, VOC exposure also significantly decreased the expression of epidermal barrier-related genes in HaCaT cells (FLG, FLG2, and loricrin). Recent evidence has demonstrated that emissions from oriented strand board, including VOCs, are significantly associated with cutaneous inflammation and impaired barrier function, contributing to the development of AD (Schneider et al. 2025). Consistent with these findings, our in vitro results provide direct experimental evidence supporting a link between VOC exposure and the exacerbation of cutaneous allergic inflammation.
These findings indicate that VOC-induced toxicity is concentration-dependent. Similarly, Kastner et al. (2011) reported that formaldehyde exposure in airway epithelial cells reduced cell viability and increased cytokine production in a concentration-dependent manner. Our results are consistent with these findings. Because the skin is constantly exposed to external stimuli, we further investigated whether VOCs exacerbate inflammation induced by existing stimuli. To assess the effect of VOCs on damaged skin, HaCaT cells pre-stimulated with TNF-α were subsequently exposed to VOCs. VOC exposure (10 μg/ml) enhanced the inflammatory response compared with TNF-α stimulation alone. Furthermore, simultaneous exposure of HaCaT cells to TNF-α and VOCs (10 μg/ml) also produced a slight but reproducible increase in the inflammatory response. Collectively, these results suggest that VOCs exacerbate TNF-α-induced inflammation in keratinocytes. Our in vitro data demonstrate that exposure of human keratinocytes to VOC mixtures at noncytotoxic concentrations significantly increased the production of pro-inflammatory mediators, including IL-8 and TARC. Importantly, VOC exposure further amplified cytokine production in keratinocytes pre-stimulated with TNF-α, suggesting that VOCs may act as inflammatory adjuvants that exacerbate pre-existing skin inflammation rather than acting solely as primary irritants.
Focusing on VOCs, previous studies have suggested a possible association between indoor decoration during the prenatal period and the first year of life and an increased risk of eczema (Herbarth et al. 2006). In addition, exposure to a mixture of 22 VOCs in patients with AD has been reported to impair skin barrier function, thereby enhancing responses to house dust mite allergens through barrier disruption (Huss-Marp et al. 2006). In the present study, we investigated the relationship between dermal VOC exposure and the development of AD using a mouse model. Topical application of a VOC mixture significantly aggravated AD symptom scores and increased ear skin thickness. Previous reports have shown that certain individual VOCs exhibit strong skin irritancy, promote Th2-type immune responses, and exacerbate allergic symptoms (Xu et al. 2002; Saito et al. 2011). Consistent with these findings, our immunological analyses revealed modest but significant exacerbation of disease-associated immune responses, including increased effector T-cell populations and elevated IL-13 gene expression.
In contrast to earlier studies reporting VOC-induced disruption of skin barrier function (Huss-Marp et al. 2006), we did not detect significant impairment of barrier function following topical VOC exposure in this model. In the present study, a mixture of 48 major indoor VOCs was applied topically at a concentration of 10 μg/ml in a mite-induced AD mouse model. Although the overall effects were relatively mild, VOC exposure nonetheless resulted in measurable worsening of AD-like symptoms. These findings suggest that, even at concentrations within guideline-relevant ranges, VOCs can function as aggravating factors in allergic skin disease rather than as primary inducers of barrier dysfunction.
The exacerbation of AD-like symptoms observed in this study is likely mediated by multiple, interrelated mechanisms involving both local cutaneous responses and systemic immune modulation. In vivo, topical VOC exposure aggravated disease severity and was accompanied by epidermal hyperplasia, inflammatory cell infiltration, and enhanced Th2-associated immune responses, including increased IL-13 expression. IL-13 is a key mediator of AD pathogenesis, promoting epidermal thickening, pruritus, and immune cell recruitment while suppressing epidermal differentiation (Zhang et al. 2025). Consistent with this mechanism, removal of VOCs via chemical filtration resulted in increased expression of FLG-related genes, suggesting partial restoration of skin barrier integrity. Because FLG deficiency facilitates allergen penetration and perpetuates cutaneous inflammation, preservation of barrier function likely contributes to the preventive effects of VOC-free air exposure observed in this study.
In addition to local skin effects, inhalation exposure to VOCs may exacerbate AD through systemic immune mechanisms. Inhaled VOCs are known to activate airway epithelial cells and lung-resident immune populations, leading to the release of pro-inflammatory cytokines and chemokines that may enter systemic circulation and influence immune responses at distal sites, including the skin (D’Amato et al. 2000; Tin Tin Win et al. 2007). Although pulmonary endpoints were not directly assessed in the present study, the more pronounced preventive effects observed with inhalation exposure to VOC-free air, compared with the relatively modest effects of topical VOC exposure, suggest that systemic inflammatory signaling initiated in the respiratory tract may play an important role in disease exacerbation.
These results suggest that VOCs may exert adverse effects even at concentrations within guideline values, underscoring the importance of strategies to minimize indoor VOC levels. To address this issue, we developed a device capable of removing VOCs and investigated its efficacy. In this study, PVC, which is widely used in building materials and furniture, was employed as the VOC source. Notably, 2-ethyl-1-hexanol, a compound released from PVC, has been identified as a causative agent of sick building syndrome; therefore, PVC was selected for this experiment. Operation of the fabricated CF system markedly reduced indoor TVOC levels. Interestingly, when the CF system was stopped, TVOC concentrations increased again, indicating that VOC emission from building materials is essentially continuous. In newly constructed buildings, high levels of TVOCs are typically detected but gradually decrease over several months. Furthermore, previous studies have reported that VOC emissions increase at higher temperatures, suggesting seasonal variation in VOC release (Chin et al. 2014). In addition, VOCs are emitted from newly introduced furniture and commonly used household detergents. Taken together, these findings underscore the importance of incorporating effective VOC removal systems. Our results suggest that implementation of such systems is necessary to maintain healthier indoor environments.
To date, no studies have investigated the effects of VOC removal on the prevention of skin disease onset. We hypothesized that inhalation exposure to VOC-free air would suppress the development of AD and evaluated this possibility. Compared with the room-air group, the CF-air group exhibited a slower increase in AD scores, skin thickness, and TEWL. Examination of factors associated with the Th2 response also revealed significant suppression in the CF-air group. Furthermore, expression of FLG, a protein essential for maintaining barrier function, was relatively increased. Th2 cytokines (IL-4 and IL-13) are known to downregulate FLG expression, thereby impairing barrier function (Howell et al. 2009). Our findings suggest that a similar mechanism was involved in this study. Because disruption of the skin barrier facilitates allergen penetration, maintaining barrier function is a critical factor in preventing exacerbation of skin diseases. Thus, the observed enhancement of barrier function under VOC-free air exposure represents a valuable outcome. Importantly, VOC-free air exposure demonstrated preventive effects against AD development. However, when we further investigated its therapeutic potential, no significant treatment effect was observed. These findings indicate that environmental modification alone has limitations in disease management.
Several limitations of the present study should be acknowledged. Although the chemical filtration system was designed primarily for VOC removal, minor co-removal of non-VOC reactive species, such as ozone or nitrogen oxides, cannot be completely excluded. In the controlled animal room environment used in this study, background levels of particulate matter and reactive gases were expected to be low and stable, and TVOC concentration was the only air pollutant quantitatively monitored and intentionally manipulated. Nevertheless, because non-VOC pollutants were not directly measured, their potential contribution to the observed improvement in AD-like symptoms cannot be fully ruled out. Future studies employing controlled exposure chambers with comprehensive monitoring of individual pollutants will be required to definitively isolate VOC-specific effects. In addition, this study did not include a VOC-alone exposure group. The experimental design was intentionally focused on evaluating VOCs as environmental modifiers that exacerbate allergen- or hapten-induced AD rather than as independent disease-inducing agents, which more closely reflects real-world exposure scenarios in susceptible populations.
VOCs are present not only outdoors but also indoors, where they can undergo chemical reactions to generate secondary pollutants such as PM_2.5_ and ozone, both of which are associated with adverse health outcomes. In the present study, dermal exposure to VOCs modestly exacerbated AD symptoms, whereas inhalation exposure to VOC-free air produced more pronounced protective effects. This discrepancy suggests that systemic inflammatory responses may play a role. Inhaled VOCs are known to activate airway epithelial and immune cells, leading to the release of inflammatory mediators that may enter systemic circulation and influence distal organs, including the skin (Jackson et al. 2025; Navarrete-Aliaga et al. 2025; Sert and Yesil-Celiktas 2025). However, pulmonary endpoints such as lung histopathology, airway inflammation, or respiratory cytokine production were not assessed in this study. Consequently, direct evidence for lung-mediated systemic effects at the VOC concentrations used is currently lacking. Future investigations incorporating detailed pulmonary assessments will be necessary to clarify the contribution of inhalation-induced systemic inflammation to VOC-associated exacerbation of AD.
In summary, the present study demonstrates that indoor VOC levels, particularly in medical environments such as veterinary clinics, can be higher than anticipated and that exposure to these compounds contributes to the exacerbation of inflammatory skin diseases, including AD, in a mouse model. It was also confirmed that use of the VOC removal device we developed can suppress the development of AD symptoms. However, this study showed that VOC removal with our device alone has limitations in improving existing skin symptoms and must be combined with other treatments, such as pharmacological therapy (e.g. glucocorticoids). Furthermore, because this device simultaneously removes not only VOCs but also other chemicals and particles, its effectiveness may not be limited to VOC removal but may also result from a comprehensive reduction of multiple environmental factors. Previous epidemiological studies have reported that VOC exposure levels are associated with differences in blood and urinary biomarkers (Lee et al. 2022). This should be examined in future studies to demonstrate the direct efficacy of VOC removal on AD development.
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