by Blake Marleau Snyder
MD Candidate – Class of 2018, University of Colorado School of Medicine
Most skin cancers are a direct result of exposure to the ultraviolet (UV) rays in sunlight. Both basal cell and squamous cell cancer (the most common types of skin cancer) as well as melanoma (a more serious and deadly skin cancer) are directly related to sun exposure, as well as indoor tanning . Nearly 99% of non-melanoma skin cancers and 95% of melanoma are caused by too much UV radiation from the sun or other sources such as tanning beds .
How Does Sun Exposure Cause Skin Cancer, Specifically Melanoma?
In short, the answer is UV radiation. But what does that really mean? Well, to begin, there are two main types of UV radiation that have damaging effects to our skin, both of which contribute to the development of skin cancer and melanoma. While UVB (shorter wavelength) radiation is more directly related to the sunburns you see, UVA (longer wavelength) radiation penetrates more deeply. 
UV radiation from the sun or tanning beds directly causes damage to DNA in your skin cells. If enough DNA damage builds up over time, it can cause cell mutations that can lead to out-of-control cell growth, which can then lead to skin cancer. Your body has natural repair mechanisms to handle this physiological stress, but they are not perfect and can sometimes lead to the development of skin cancers, including melanoma. An example of this DNA damage many of us know all too well. If the sun damages skin cells so severely that they must be destroyed, peeling after sunburn can occur as your body’s way of getting rid of damaged skin cells that could lead to cancer if not removed. While skin peels and new skin layers form, some damage can still remain, especially in deeper layers. It is for this reason that it is important to try to avoid burning in the first place.
Once cancers arise on the skin surface melanoma and non-melanoma skin cancers can be invasive, growing down through the deeper layers of skin and beyond. If the tumor grows through the wall of a blood or lymph vessel, cancer cells can break off and spread to other parts of the body, or metastasize. This is why skin cancer is usually easier to treat successfully when it is caught at an early stage, before it spreads. For this reason it is important to frequently check for the ABCDEs of melanoma explained in our tab, “The ABCDEs of Melanoma Screening.”
What are the Sources of UV Radiation & Who is at Particularly High Risk?
As we have stated above, studies at the National Institutes of Health and elsewhere have shown that exposure to UV radiation increases your risk of getting melanoma, especially if you had sunburns during childhood . The main source of UV radiation which we receive is from the sun, however, there are a few sources of artificial UV radiation we should all be aware of in order to prevent the development of skin cancers.
Indoor tanning beds are by far the largest source of artificial UV radiation within the general population, however, welding, metal work, and phototherapy also increase UV exposure. Some believe that indoor tanning beds are a safer way to tan, but this is not true. Tanning beds use a different mixture of UV radiation than natural sunlight, which is often much stronger. Similarly to natural sun exposure, indoor tanning significantly increases the likelihood of developing nearly all skin cancers, including melanoma. It is for this reason that many government organizations as well skin cancer prevention advocacy groups have issued the following statements:
-International Agency for Research on Cancer (IARC) classifies the use of UV-emitting tanning devices as “carcinogenic to humans.” This includes sunlamps and sunbeds (tanning beds).
-The National Toxicology Program (NTP) has stated that exposure to sunlamps or sunbeds is “known to be a human carcinogen.”
-The US Food and Drug Administration (FDA), which now refers to all UV lamps used for tanning as “sunlamps,” requires them to carry a label that states, “Attention: This sunlamp product should not be used on persons under the age of 18 years .”
Why are Childhood Burns So Bad?
It has been reported that severe sunburns during childhood or adolescent years are more than twice as likely to progress to cancer than burns later in life . Now, this certainly does not mean that adults are alleviated of this danger, and should remain conscious and avid users of sun protective measures, but why are young particularly at risk? One reason is the type of cancer that often develops as a result of overexposure to UV rays at different points in one’s life. While sun exposure both in childhood and adulthood can proceed to non-melanoma skin cancers, melanoma risk is predominantly associated with greater exposure to UV rays earlier in life. For this reason, it is particularly important that parents are advocates of sun protective measures and positive role models of these techniques for their children’s safety.
FDA dermatologist Markham Luke, M.D., Ph.D. states, “Many experts believe that at least one reason for the rise in melanoma is the increased use of sunlamp products by U.S. teenagers and young adults.” It is believed that adults are much more conscious of the detrimental effects of sunburning, and thus are significantly more apt to prevent such burns. A recently published study within the journal Cancer Epidemiology, Biomarkers & Prevention demonstrated that people who experience as few as five burns between the ages of 15 to 20 are 80% more likely to develop melanoma as those who do not experience sunburning .
How Do We Prevent It?
While melanoma is one of the deadliest cancers, it is also one of the most preventable types of cancer that we know of currently. In the UK more than 8 in 10 cases of melanoma, the most serious type of skin cancer, could be prevented through enjoying the sun safely and avoiding sunburn .
This leads to the question, what is sunburn? Sunburn doesn’t have to be raw, peeling or blistering–if your skin has gone pink or red in the sun, it is sunburnt. The heat you feel from the sun is due to infrared rays, which is not the cause of sunburn or DNA damage, that is why you can still burn on cool days. Sunburn is the most obvious way to tell that the DNA in your skin cells has been damaged by too much UV radiation. Individuals who get a painful sunburn only once every two years have three times the risk of developing melanoma skin cancer than those who use proper sun safety techniques .
Getting sunburnt doesn’t mean you will definitely develop skin cancer, but the more frequently you sunburn, the more likely you are to develop the disease. Like many of us, if you have had sunburn in the past, it’s a good idea to think about what more you can do to protect your skin next time (and below we provide you some helpful tips).
The Skin Cancer Foundation gives these tips to Prevent Skin Cancer:
- Seek the shade, especially between 10am and 4pm.
- Do not burn.
- Avoid tanning and UV tanning beds.
- Cover up with clothing, including a broad-brimmed hat and UV-blocking sunglasses.
- Use a broad spectrum (UVA/UVB) sunscreen with an SPF of 15 or higher every day. For extended outdoor activity, use a water-resistant, broad spectrum (UVA/UVB) sunscreen with an SPF of 30 or higher.
- Apply 1 ounce (2 tablespoons) of sunscreen to your entire body 30 minutes before going outside.Reapply every two hours or immediately after swimming or excessive sweating.
Keep newborns out of the sun. Sunscreens should be used on babies over the age of six months.
- Examine your skin head-to-toe every month.
- See your physician every year for a professional skin exam .
To see what happens to your skin when it burns, check out the video below: