In the case of incomplete or defective repair of so-called mutated cells.

Certain mutated cells can also proliferate, on this basis, a tumor can arise (Melanoma, Basal Cell Carcinoma, actinic keratoses, Squamous).
The tumor formation is compounded by a UV-induced weakening of the immune system favors the skin.
The premature aging of the skin (actinic elastosis) is mainly due to UVA:
There is a thickening of the skin by increasing cell regeneration and disturbances in the formation of the cells.
The connection between the elastic fibers and collagen will be eased partially dismantled. The skin becomes flabby and prone to wrinkles.
There is a piebald pigmentation of the skin
increased occurrence of age spots
and a cosmetically disturbing widening of blood vessels.