Skin exposure to sunlight causes thickening of the stratum corneum, increased melanin production, and DNA protection from UVA and UVB radiation.

“physiologic response i'm quoting from the article of skin exposure to sunlight is thickening of the stratum corneum the outermost layer of the epidermis and increase skin pigmentation through production of melanin as i suggested this pair response response actually protects the skin and deeper tissues from the deeper penetrating and damaging uvas while retaining benefits of uvb exposure though both uva and uvb exposure result in increased skin pigmentation the mechanisms are different with uvb being responsible for the up regulation of melanin synthesis and thus the protective effects against uv damage to dna”