There are many different types of skin cancer. The most common form of skin cancer is called solar keratosis or actinic keratosis. The words solar and actinic refer to the sun. Sunlight causes solar keratosis by damaging the DNA inside the cell. The damage occurs due to the effect of sunlight on the DNA inside the cell nucleus. DNA has a tendency to absorb ultraviolet radiation with wavelengths between 220nm and 300nm. These are the wavelengths of UVC and UVB. UVC however does not normally reach the surface of the earth and the big DNA damaging culprit is therefore UVB.
Repeated exposure to sunlight eventually causes irreparable damage to the DNA inside the cell and this leads to the development of solar keratosis. Solar keratosis is the earliest manifestation of squamous cell carcinoma. The difference between squamous cell carcinoma and solar keratosis is a matter of degree. Squamous cell carcinoma has started to involve the second layer of the skin, the dermis, already. Solar keratosis is limited to the lower layers of the epidermis.
It is very important to treat solar keratosis and not wait for its further development, because squamous cell carcinoma is much more dangerous and has the ability to spread throughout the body.