Introduction: Patch testing of contact allergens to diagnose allergic contact dermatitis (ACD) is a traditional, useful tool. The most important decision is the distinction between allergic and irritant reactions, as this has direct implications on diagnosis and management. 

Objectives: To evaluate a new method of non-contact infrared reading of patch tests and a possible correlation between the intensity of the patch test reaction and temperature change.

Patients/Materials/Methods: 30 positive reactions from 14 patients were included in our study. An independent patch test reader assessed the positive reactions and classified them as allergic (of intensity + to +++) or irritant (IR). At the same time, a forward-looking infrared (FLIR) camera attachment for iOS was used to acquire infrared thermal images of the patch tests, and images were analyzed using the FLIR ONE app.

Results: Allergic patch test reactions were characterized by temperature increases of 1.09 ± 0.4°C compared to surrounding skin. Irritant reactions only resulted in 0.12 ± 0.1°C temperature increase. The difference between the two groups was highly significant (p < 1.04 x 10-8). 

Conclusion: Thermography is a reliable and effective way to distinguish between allergic and irritant contact dermatitis.

Non-contact reading of patch tests utilizing infrared imaging