What Causes Skin Cancer?

Couple walking in sunlight with dogExposure to ultraviolet (UV) radiation is the greatest cause of the most common skin cancers. UV radiation, in the form of light, can come either from the sun or from indoor tanning beds. Basal cell and squamous cell cancers, by far the most common types of skin cancer, are directly related to the total dose of UV light that the skin receives over a lifetime of exposure.

Contrary to popular belief, most individuals do not receive higher exposures to UV radiation during childhood, but rather have a relatively constant exposure rate over their lifetime. This is why sun protection is so important for all individuals, not just children. 

Here’s a useful analogy. Think of sun exposure as drops of water inside a measuring cup. We add a drop or two of water every time we are exposed to the sun. The red marker lines on the side of the measuring cup indicate the radiation dose required to trigger a skin cancer. 

Those lines are at different places on the measuring cup for each person, but they generally start toward the top of the cup. After many years and many drops, the water level hits the first red marker, and a skin cancer may appear. After your first skin cancer, the lines on the cup start getting closer together, and every exposure keeps adding water to the cup.

We may slow the addition of “water” by reducing exposure, but we really can’t stop it altogether. This is why every bit of sun exposure is so important. It is also why dermatologists want to see patients frequently after the first skin cancer is diagnosed. We’re on the lookout for more to develop because a new skin cancer is more likely to occur in individuals who have recently had one.

Other causes of nonmelanoma skin cancer include exposure to substances capable of causing cancer (carcinogens) such as arsenic, which is occasionally found in well water and was historically present in insecticides. Skin cancer can also develop in patients with decreased functioning of the immune system (ie, those with chronic immunosuppression), which is commonly triggered by medications following organ transplant surgery. Skin cancer may form in skin that was injured by a thermal burn or a radiation treatment. A long-standing, nonhealing wound can also develop skin cancer over time. There are genetic syndromes that lead to the early and frequent development of skin cancers as well.  

The causes of the more-deadly melanoma are more difficult to determine and are likely a combination of factors. Identified risk factors include having a history of sunburns, fair skin that doesn’t easily tan, red or blonde hair, or many moles, especially large or unusual ones. Having a personal or family history of melanoma also increases the risk that another melanoma will occur.

Because early detection is so important in increasing the chances of survival after a melanoma, people with any of the risk factors above should see a trained dermatologist for a regular skin exam.

Cure rates and cosmetic outcomes after the treatment of nonmelanoma skin cancers are also affected by early diagnosis. So any new, nonhealing skin lesion should be evaluated by a dermatologist. For more information about skin cancer, including how to perform self-examinations and what to look for, please visit these links:

American Academy of Dermatology
Skin Cancer Foundation
American Society for Dermatologic Surgery

And if you find any new, unusual, or nonhealing lesion on your body, your dermatologist will want to see it. Feel free to bring photographs or circle the lesions you’re worried about – this way you won’t forget to ask.

Published on 05/14/2009 | Last updated on 12/20/2016