Importance: Sun damage is the most important environmental factor associated with malignant melanoma. To address the health threat, as well as the economic burden, primary prevention and early detection are crucial.
Objective: To test the efficacy of a topical sunscreen in the prevention of UV-induced effects in nevi.
Design: Prospective study of nevi protected by sunscreen vs a physical barrier.
Setting and patients: Twenty-three nevi from 20 patients attending a referral hospital.
Intervention: Half of each nevus was protected by either a physical barrier or a sunscreen. Lesions were completely irradiated by a single dose of UV-B.
Main outcomes and measures: In vivo examination before and 7 days after irradiation and histopathologic-immunopathologic evaluation after excision on the seventh day.
Results: The most frequent clinical changes after UV radiation were pigmentation, scaling, and erythema; the most frequent dermoscopic changes were increased globules/dots, blurred network, regression, and dotted vessels. Both physical barrier- and sunscreen-protected areas showed some degree of these changes. More than 30% (7) of nevi did not show any change on clinical examination, and 18% (4) had no dermoscopic change. Immunohistopathologic differences between the halves of each nevus were demonstrable even when in vivo examination detected nothing. Parakeratotic scale, increased number and activation of superficial melanocytes, and keratinocyte proliferation were the most remarkable features. The only difference between both barriers was more enhanced melanocytic activation and regression features in the sunscreen group. No phenotypic features were found to predict a specific UV-B response.
Conclusions and relevance: Both physical barriers and sunscreens can partially prevent UV-B effects on nevi. Subclinical UV radiation effects, not always associated with visible changes, can develop even after protection. Sunscreens are not quite as effective as physical barriers in the prevention of inflammatory UV-B-induced effects.