The Effect of Ultraviolet Irradiation on Epidermal Melanocyte After Sunscreen Application

Over-exposure to sunlight may result in sunburn, pigmented skin lesions, solar keratosis, premature aging of skin, or cancer in human skin. Sunscreens protect the structure and function of the human integument from the actinic damage. This protective effect is afforded by active ingredients of sunscreens through absorption, reflection, and/or scattering of the solar radiation impinging on the skin. There are oral and topical sunscreens. Para-aminobenzoic acid(PABA), PABA esters, benzophenones(BZ), cinnamates, salicylates and anthranilates are the topical sunscreens absorbing solar radiation. Most of them absorb UVB, but BZ absorb both UVB and UVA. These investgators observed the effect of the sunscreens by calculating sun protection factor(SPF) before and after application of the sunscreens in human skin. To my knowledge, there are no papers which evaluate morphological changes in the epidermal melanocytes after UVB or UVA irradiation following application of the sunscreens. In this experiment, a total of 150 adult male black mice(C57BL) was used. The animals were divided into one control (application of hydrophilic ointment base) and four experimental(application of PABA, Cinnamate, BZ or homomenthylsalicylate (HMS)) groups. Each group was irradiated by UVB and UVA, respectively. Each of the 5 groups were divided into 5 subgroups according to the days of UV light irradiation ; subgroup A for 2 days, B for 4 days, C for 6 days, D for 8days and E for 10 days. The daily doses of UVB and UVA were 50mJ/cm^2 and 5J/cm^2 respectively. YS UVB-400 and Waldmann UV 800 were used as a light source of UVB and UVA. Skin specimens were taken from both ears of the animals 24h after the last irradiation. The split-DOPA preparation was carried out for observation of the numbers and morphological changes of the epidermal melanocytes. The results are summarized as follows; 1. Changes in the numbers of the epidermal melanocytes : The numbers of the epidermal melanocytes markedly decreased in the experimental groups, especially in the group of PABA application(p<0.01), compared in the control group under UVB irradiation (p<0.01). However, only the group of BZ application showed a significant decrease in the numbers compared to the control group under UVA irradiation(p<0.01, p<0.05). 2. Changes in the size of the epidermal melanocytes ; Each experimental group, especially the group of PABA application (p<0.01), showed a significant decrease in the sizes of the epidermal melanocytes under UVB irradiation(p<0.01, p<0.05). On the other hand, only the group of BZ application showed a significant decrease in the sizes compared to the control group under UVA irradiation(p<0.05) From the results, it seems to be sure that PABA, Cinnamate, BZ, HMS can protect UVB from sunlight in the skin of black mice. Furthermore, BZ was effective for protection of UVB and UVA together.