Repeated exposure to UVB over the course of one s life can cause skin cancer and alter the immune system. UVC rays are the strongest, most dangerous rays. However, little attention is given to UVC rays as they are normally filtered by the ozone layer and do not reach the Earth. This usually starts as a flat brown spot that looks like a freckle. The edges are irregular and the whole spot is most likely asymmetrical.
Patients often describe such a mole as resembling a squashed bug.
It can grow and eventually becomes crusted. The crust may drop off and heal with a new crust forming. Usually the spot is clear or flesh coloured, but sometimes the spot may be pigmented. The latter are areas of chronic scaling with discoloration, usually pink or brown. They occur on sun exposed areas.