# Active Versus Passive Infrared Thermography for Skin Cancer Detection: A Diagnostic Accuracy Study

## TL;DR

Active infrared thermography is better than passive thermography at detecting skin cancer, offering a low-cost, non-invasive option for early detection in areas with limited access to specialists.

## Contribution

The study demonstrates that active thermography significantly improves sensitivity for detecting malignant skin lesions compared to passive thermography.

## Key findings

- Active thermography achieved 91.1% sensitivity and 75.0% specificity for detecting malignant lesions.
- Passive thermography had low sensitivity (17.9%) despite 100% specificity.
- Active thermography showed an AUC of 0.871, significantly higher than passive imaging's 0.650.

## Abstract

Skin cancer is highly curable when detected early, but access to specialist evaluation and advanced diagnostic tools remains limited in many settings. Infrared thermography is a non-invasive imaging technique that measures skin temperature and may help identify abnormal tissue. In this study, we compared two thermographic approaches—passive imaging at rest and active imaging after brief cooling—to evaluate their ability to distinguish benign from malignant skin lesions. We found that active thermography was substantially more sensitive in detecting malignant lesions, while passive imaging missed most cancers despite high specificity. Temperature differences between lesions and surrounding skin were more pronounced after cooling, improving diagnostic discrimination. These findings suggest that active infrared thermography may serve as a low-cost, non-invasive complementary tool to support early skin cancer detection, particularly in screening or triage settings where access to dermatologic care is limited.

Background: Infrared thermography has emerged as a non-invasive imaging modality capable of capturing physiological alterations associated with skin cancer; however, its diagnostic utility remains insufficiently characterized. This study aimed to compare the diagnostic performance of active (cooling-induced) and passive infrared thermography in distinguishing benign from malignant skin lesions. Methods: In this clinical study conducted at Barretos Cancer Hospital, 64 individuals contributed 100 skin lesions, of which 68 (56 malignant, 12 benign) met criteria for diagnostic accuracy analysis. Long-wave infrared images were acquired under steady-state conditions (passive thermography) and after standardized cooling (active thermography). Diagnostic performance was assessed using thermal contrast patterns and temperature differentials (ΔT), with histopathology as the reference standard. Results: Active thermography markedly outperformed passive imaging. Active thermography achieved a sensitivity of 91.1% and specificity of 75.0%, whereas passive thermography demonstrated low sensitivity (17.9%) despite perfect specificity (100%). Malignant lesions displayed substantially higher ΔT values, particularly during active thermal recovery. ROC analysis confirmed the superiority of the active technique (AUC = 0.871) over passive imaging (AUC = 0.650), with an optimal ΔT cutoff of 0.70 °C yielding high discriminative accuracy. Conclusions: Active infrared thermography enhances thermal contrast and provides significantly improved diagnostic sensitivity compared with passive imaging. As a low-cost, non-invasive technique, active thermography shows promise as a complementary tool for skin cancer triage, particularly in settings with limited access to dermatologic evaluation.