Changes in common melanocytic naevi after intense sun exposure: digital dermoscopic study with a 1‐year follow‐up

Summary Background.  Exposure to ultraviolet (UV) radiation induces acute changes in common melanocytic naevi (CMN). Aim.  To analyse changes in size and dermoscopic structures of CMN in healthy individuals under the influence of intense sun exposure and to investigate effectiveness of sunscreen usage in preventing the appearance of dermoscopic changes. Methods.  The subjects were divided into an SS group and a non-SS group, according to whether they used sunscreen or not. Digital epiluminiscence microscopy (DELM) was performed before sun exposure and 28 days and 1 year after the cessation of intense sun exposure. Results.  Eleven subjects with 60 naevi fulfilled the inclusion criteria. A significant increase in one diameter of the CMN was found 28 days after cessation of sun exposure, irrespective of sunscreen usage. There was no significant change in total dermoscopy score during the follow-up period in either the SS or non-SS group. There were definitive DELM changes at the 1-year follow-up in 10% of CMNs < 5 mm in size. Changes in pigmented network, globules and streaks were fully reversible in the remaining CMN. The use of sunscreen had no influence on these changes. Conclusions.  The increases in the size of melanocytic naevi that we found 28 days after cessation of intense sun exposure are probably induced by UV radiation, whereas changes in DELM features that were not reversible in some small naevi at the 1-year follow-up could be related both to sun exposure and to the natural evolution of the naevi. The use of sunscreen does not seem to prevent these changes. Small naevi in low-risk young and middle-aged patients seem to be more prone to sun-induced DELM changes.