Sun exposure, sunscreen and their effects on epidermal Langerhans cells.

This study examined the effects of chronic and current sun exposure on the number of Langerhans cells in epidermal sheets of UV-exposed and unexposed skin of the arms and assessed the effect of sunscreens. Participants were enrolled in a skin cancer prevention trial and had been using sunscreen daily for the previous 3 years. There were significantly fewer Langerhans cells on the exposed (463 cells/mm2) than on the unexposed forearm (528 cells/mm2) (P = 0.0001). High sun exposure in the previous 2 weeks and a history of predominantly outdoor occupations were both associated with a reduced number of Langerhans cells, although age and other biological indicators of chronic exposure were not associated. Sunscreen use was protective against the effects of current but not chronic sun exposure, with a suggestion of a greater effect at higher levels of exposure. Unexpectedly, people with a past history of nonmelanoma skin cancer had more Langerhans cells in both the exposed and the unexposed skin. These results emphasize the need for continued public health education to protect the immune system from the damaging effects of UV radiation.