Different responses of the melanin index to ultraviolet irradiation in relation to skin color and body site

Summary Background/Purpose Few reports describe UVB irradiation‐induced pigmentation responses from different skin colors or from different body sites. This study determined pigmentation changes in skin with different colors and from different body sites following 308‐nm excimer laser irradiation. Methods Ten healthy Korean adults were divided into light‐ and dark‐skin groups, and irradiated body sites were divided into unexposed zones (UZ), intermittently exposed zones (IEZ), and frequently exposed zones (FEZ). Twenty‐four areas were irradiated with a single 300‐mJ/cm2 shot delivered by an excimer laser. MIs were measured before irradiation, immediately after irradiation, and then 1 day, 3 days, 7 days, 14 days, and 21 days after irradiation. Results MIs declined significantly on day 1 after irradiation, particularly in light‐colored skin. In the light‐skin group, the MI increased from day 3 after irradiation and continued to increase for 21 days, whereas in the dark‐skin group, the peak MI was reached at 7 days and declined thereafter. The peak MIs were reached at 7 days in the IEZ and FEZ and at 14 days in the UZ. Conclusion Following UVB irradiation, MIs decreased, particularly in light‐colored skin, before delayed tanning developed. UVB‐induced pigmentation varied according to different skin colors and the body sites irradiated.