Effects of Skin Temperature on UV-induced Erythema and Pigmentation in Human Skin in Vivo

Background : Skin temperature at UV radiation exposure influences acute skin reaction such as erythema and pigmentation. As most biochemical systems are affected by temperature, thermal change preceding or following UV exposure could influence the responses in the way to cause vascular blood flow and change the inflammatory reponse. Objective : To investigate the influence of thermal change on UV-induced erythema and pigmentation by using objective and quantitative method. Methods : A sunlight fluorescent sunlamp (Waldmann UV 800) was used as a UV light source. Multiple sites of the lower back were irradiated with increasing doses of UV, which were preceded or followed by heating or cooling. With a reflectance spectrophotometer, we assessed erythema and melanin indices at control, 0.1, 0.5, 1.0 and 2.0 MED dose-exposed sites. Results : Compared with the only UV-exposed group, skin warming or cooling groups generally showed elevated acute erythema reaction with higher erythema indices. However, thermal changes preceding or following UV exposure had little effect on pigmentation except the post-warming group with UV exposure of 2 MED dose after 2 weeks. Our results indicate that altering the skin temperature modulates the degree of UV-induced erythema, but generally not skin pigmentation. Conclusion : The results in this study show that environmental factors such as heat or cooling have modulating effects on UV-induced skin reaction. These interactions should be considered when dealing with the effects of natural sun exposure or phototherapy.