The effects of chronic sunscreen use on the histologic changes of dermatoheliosis

BACKGROUND: Sunscreen application to the skin of hairless mice is effective in reversing the histologic changes associated with photoaging (solar elastosis, epidermal thickening, collagen depletion, glycosaminoglycan deposition). These reparative processes have not been studied in human beings. OBJECTIVE: The aim of this study was to evaluate histologically the effects of daily application of a UVA/UVB sunscreen versus placebo. METHODS: We examined 46 patients who were given either sunscreen or vehicle and asked to apply it daily for 24 months. Punch biopsy specimens were obtained from preauricular skin at 0, 12, and 24 months. Each specimen was examined for epidermal thickening and organization and dermal inflammatory infiltrate by light microscopy. Computer-generated analysis of tissue sections was used to evaluate solar elastosis. RESULTS: A significant difference in solar elastosis was found between the treatment groups; however, the other features remained largely unchanged. CONCLUSION: The dermal changes of photoaging may be affected differently than epidermal changes when UV radiation exposure is diminished. UVA and UVB may contribute diversely to these cutaneous changes. Computer-generated evaluation of dermatoheliosis may be more accurate than visual inspection.