Electronic infrared thermography as a method of assessing herpes labialis infection

The purpose of this study was to ascertain the applicability of infrared thermography to study the natural history of herpes labialis lesions. Since thermography is capable of detecting changes not visible to the naked eye, then it may be of value in complementing clinical examination of the various stages of herpes labialis. In addition, thermographic imaging is quantitative and therefore allows for an accurate assessment of temperature changes accompanying the disease process, both within patients and between patients. Ten female patients suffering from herpes labialis were studies (mean age 25 +/- 5 years). In all cases herpes simplex virus Type 1 was isolated by the HEP-2 technique. No treatment was instituted and patients were clinically assessed and thermographically imaged daily from the prodromal phase through to resolution. A marked temperature increase (1 degree C minimum) was observed within hours of the prodromal phase and maintained until day 4. As the lesions progressed to vesicle formation, the central area of the vesicle was noted to be cooler due to the insulating effect of the fluid. Even by day 6 a significant 0.5 degree C temperature increase over background was present at the involved site and this returned to normal within 8 to 10 days. The area of thermographic involvement was three to four times larger than the clinical area of involvement (60-100 mm2 versus 20-25 mm2). To assess reproducibility, we also studied patients through two additional untreated herpes labialis episodes. The prodromal phase was reproducible thermographically and characterized by a temperature increase of 1.42 degrees C +/- 0.2 degrees C. Thermographic imaging may represent a new approach to quantifying disease activity in herpes labialis, particularly in the subclinical prodromal stage.