All types of Skin Cancer occur when mutation or any kind of error develops in the DNA of the outermost layer of skin cells. These mutations lead to the uncontrollable growth of skin cells, which form a mass of cancer cells. Basal cell Skin Cancer is generally caused by ultraviolet radiation from the sun or tanning beds. These UV rays damage your DNA, and your cells start multiplying unusually. The squamous cell Skin Cancer also develops due to exposure to UV radiation. This type of cancer can also be developed due to long time exposure to cancer-causing chemicals. This may occur within a burn scar or an ulcer and may also be caused by some viruses like- (HPV) human papillomavirus. The main cause of melanoma is not clear until now and not every mole turns into melanoma. Like basal and squamous cell skin cancers, melanoma is caused by UV rays, but melanoma can also develop in the parts of the body that are not generally exposed to sunlight.