Tanning is the skin's response to ultraviolet (UV) light--a protective reaction to prevent further injury to the skin from the sun. However, tanning does not prevent skin cancer.
Aside from exposure to UV light (from the sun or manmade sources, such as tanning lamps), the following are possible risk factors for skin cancer:
Heredity. People with a family history of skin cancer are generally at a higher risk of developing the disease. People with fair skin and a northern European heritage appear to be most susceptible.
Multiple nevi (moles) or atypical moles
Exposure to coal and arsenic compounds
Elevation. Ultraviolet light is stronger as elevation increases (because the thinner atmosphere at higher altitudes cannot filter UV as effectively as it does at sea level).
Latitude. The rays of the sun are strongest near the equator.
Repeated exposure to X-rays
Scars from disease and burns
Immune suppression, such as in people who have had organ transplants
Prior history of skin cancer
Certain rare inherited conditions, such as basal cell nevus syndrome (Gorlin syndrome) or xeroderma pigmentosum (XP)
Smoking (increases the risk for squamous cell cancer, especially on the lips)