# Prenatal and Childhood Exposure to Humidifier Disinfectants and Attention-Deficit/Hyperactivity Disorder (ADHD): Insights from a Retrospective Cohort Design

## TL;DR

Prenatal and early childhood exposure to humidifier disinfectants is linked to a higher risk of ADHD, according to a study of over 1,500 individuals.

## Contribution

This study is the first to explore the association between humidifier disinfectant exposure and ADHD risk using a cohort of claimants.

## Key findings

- ADHD incidence was 4.782 per 1000 person–years among HD claimants.
- Higher cumulative exposure duration and early-life exposure were associated with increased ADHD risk.
- Adjusting for sociodemographic factors confirmed a significant hazard ratio for ADHD with prolonged exposure.

## Abstract

Humidifier disinfectants (HDs), also known toxic indoor chemicals, have been linked to adverse health outcomes in children. However, their association with ADHD development remains largely unexplored. This study aimed to investigate the incidence of ADHD among HD claimants and assess the association between HD exposure and ADHD risk. A cohort of HD damage claimants born between 2002 and 2011 was established. ADHD cases and controls were identified using matched National Health Insurance Service claim data, with follow-ups required until age 10. ADHD incidence was calculated, and exposure characteristics—including the use of PHMG/PGH, humidifier distance and location, and cumulative and annual exposure duration—were analyzed. Cox proportional hazards analysis was performed, adjusting for sociodemographic factors and comorbidities. Among 1597 subjects, 84 were diagnosed with ADHD, resulting in an incidence density of 4.782 per 1000 person–years. Higher cumulative exposure duration and hours significantly increased the hazard ratio (HR) for ADHD. Additionally, exposure during the first three years after birth was associated with a higher HR for ADHD. These findings suggest that ADHD incidence is elevated in HD claimants and that HD exposure, particularly prolonged or early-life exposure, is associated with increased ADHD risk. Further research is required to confirm these findings in exposed cohorts and to elucidate the mechanisms underlying HD-related ADHD.