Squamous cell carcinoma is usually caused by cumulative ultraviolet (UV) exposure. It’s development is gradual over a course of a lifetime. Exposure to UV lights over years via tanning on the beach during the summer and/or the use of tanning beds are all contributors to maturation. It will generally appear in the areas that have been most exposed to UV light, such as the head, neck and the back of the hands. Women often have it on their lower legs.