The Truth About How Suntanning Causes CancerS

You've heard the myths. If you get a tan, you won't get skin cancer. If you use SPF 50 sunblock, you're safe. Only people with light skin are prone to skin cancer. None of these are true.

It's suntan season in the Earth's northern hemisphere, so you'd better get the facts. We've got the lowdown on the real connection between going out in the sun and getting skin cancer — and some recommendations about how to protect yourself while also soaking up some healthy solar radiation.

Any doctor will tell you that getting sun is good for your health. Vitahimin D, crucial for bone and immune system health, is activated in your body when you expose your skin to sunlight. Some medical experts say just a half hour or more of exposure to sunlight will cause an enormous amount of the vitamin to circulate in your bloodstream. But too much sunlight can be deadly.

The Truth About How Suntanning Causes CancerS

A suntan, like a sunburn, is produced by exposure to the ultraviolet radiation found in sunlight. Both sunburn and suntan are caused when ultraviolet rays damage your DNA, which can be the first step on the pathway to cancer. Writes medical researcher Sophie Balk, in an overview of skin cancer research published this year, "According to recent evidence, the tanning response means that DNA damage has occurred in skin." She and her colleagues warn that excessive tanning can lead to cancer — and they suspect that the rise in cases of skin cancer could be connected in part with the popularity of tanning salons. Excessive tanning also breaks down the collagen in your skin, which leads to the symptoms of aging such as sagging and wrinkles.

Surgeon and cancer researcher Adam Riker recently published a paper with his colleagues on the growing dangers from skin cancers like melanoma, which are becoming more common. They write, "Melanoma is the sixth most common fatal malignancy in the United States, responsible for 4% of all cancer deaths and 6 of every 7 skin cancer-related deaths." They estimate that 1 in 5 Americans will develop some form of skin cancer in their lifetimes, which means that each year there are at least 1 million new cases in the U.S. alone. Balk adds that nonmelanoma skin cancers basal cell carcinoma (BCC) and squamous cell carcinoma (SCC) are also on the rise, with 2 million new cases every year.

Skin cancer has become such an enormous public health issue that in 2009 the World Health Organization declared ultraviolet (UV) light to be a class I carcinogen — the highest risk for cancer. A report by the International Agency for Research on Cancer, the cancer arm of the World Health Organization, found that tanning beds and other sources of ultraviolet radiation increase the risk of skin cancer by 75% for those who use tanning beds before the age of 30.

So we know skin cancer is a huge problem, and it's linked to sunlight. But how exactly does that work?

Do People With Darker Skin Need To Worry About Skin Cancer? Yes.
Doctors and medical researchers emphasize the importance of sunscreen use and self-examination regardless of race or skin type. BBC News quotes a number of experts who explain that "contrary to common perception, people with dark skin are more likely to die from skin cancer than those with fairer skin." The article warns that while dark skin may provide a greater natural skin protection factor than relatively lighter skin, "this should not lull people with darker skin into a false sense of security."

How do tanning and sunburn turn into skin cancer?

The sun emits three kinds of ultraviolet radiation, which are called A, B, and C. That's why you'll sometimes see sunblock that claims to be effective against UVA, UVB, and UVC — those letters refer to the different kinds of radiation that can affect your health. Balk explains: UVC rays possess the highest energy but do not penetrate the atmosphere. Thus, middle-wavelength (UVB) and long-wavelength (UVA) UVR . . . have the greatest biological significance. Solar radiation that reaches the earth's surface constitutes approximately 95% UVA and 5% UVB. Most UVB radiation is absorbed by stratospheric ozone, but ozone absorbs little or no UVA or visible light.

UVA radiation and visible light can produce skin darkening after a few minutes, while UVB radiation produces tans that appear several days after exposure — and these UVB tans can last for weeks. Balk points out that as the ozone layer is thinned or develops holes, this has an enormous impact on how dangerous UVB is. As Balk puts it, "UVB is absorbed by and can directly damage DNA, which ultimately leads to the development of skin cancer." By contrast UVA is absorbed much more deeply into the skin, not into the DNA itself, but it can also cause damage that leads to cancer. The WHO helped debunk the myth that ultraviolet radiation's carcinogenic properties were limited to UVB rays, showing that both UVA and UVB light have been proven to cause skin and eye cancer in humans and animals.

Different forms of skin cancer arise in different types of skin cells, but what makes a tan become cancerous boils down to the same thing: if you bombard your DNA with enough UV radiation, it will lead to errors in the DNA, leading to mutations in your genome that cause tumors. These mutations are cumulative, which is why cancers tend to occur later in life, and why overexposure to UV radiation beginning at a young age can have such a dramatic impact on an individuals likelihood of developing skin cancer.

UV radiation actually has a two-fold effect on your body. It causes genomic mutations, and also impairs the function of the tumor supressor protein p53. So excessive tanning means you're more likely to grow tumors, and less likely to have the means to suppress the spread of those tumors.

Does that mean you should hide inside, gobbling vitamin D pills and allowing only the light of computer monitors to touch your face? No. As we said earlier, some sunlight is good for you. The issue, as with any carcinogenic substance, is dosage.

The Truth About How Suntanning Causes CancerS

Dermatologist DL Narayanan and colleagues write:

There is a dose-related relationship between sunlight exposure and the incidence of skin cancer. For the development of BCC and melanoma, intermittent intense exposures appear to carry a higher risk than lower-level chronic exposures, even if the total UV dose is the same. By contrast, the risk for SCC is strongly associated with chronic UV exposure but not with intermittent exposure. Taken together, epidemiologic studies and experimental studies in laboratory animals indicate that intermittent intense and chronic exposures to solar UVR are the primary cause of NMSCs and melanoma.

Basically, what Narayanan is saying is that your risks for cancer are highest if you get one, whopping dose of sunlight once in a while; or if you are constantly exposing yourself to lots of sun every day. There are a lot of ways to avoid hitting these dose levels, however, and make yourself far less likely to get skin cancer later in life.

What can you do to prevent cancer when getting a tan?

To prevent overexposure to UVR, you want to limit your doses of sunlight. As Narayanan would no doubt say, enjoy the sun in moderation. If you rarely get out in full sunlight, don't plan a vacation that will involve three days of intensive sun exposure. Plan ways to cover up your skin, with both clothing and sunscreen, if you're going to do that. Likewise, if you work in the sun every day, make similar plans. Wear a hat; wear sunblock; cover as much of your body as possible. Also, try to take breaks in the shade or indoors during the sunniest part of the day.

The Truth About How Suntanning Causes CancerS

Solar radiation is at its most intense during mid-day, when the sun is high overhead. The strength of sunlight is published in many locations as a UV index, and varies primarily on your latitude and the time of day. Generally speaking, UV radiation increases with proximity to equatorial latitudes; the closer to the equator you are, the more UV radiation you will receive. At higher latitudes, UV rays must pass through more of the Earth's atmosphere before reaching us, and are thus lower in intensity. The amount of UV radiation reaching Earth over the course of the day depends on how high the angle of the sun is in the sky. At left you can see a UV radiation map created by NASA, showing where the most radiation is at ground level on a particular day (red is highest).

A good rule of thumb is to look at your shadow. The less of your shadow you see, the more UV radiation you'll be exposed to.

What about sunscreen? A recent research study suggests:

The best protection is achieved by application 15 to 30 minutes before exposure, followed by one reapplication 15 to 30 minutes after exposure begins. Further reapplication is necessary only after activities such as swimming, sweating, and rubbing.

But the whole SPF thing? Once you reach SPF 15, going higher doesn't make much of a difference because SPF protection doesn't increase proportionally. To give you an idea, SPF 2 absorbs 50% of UV radiation, while SPF 15 absorbs 93% and SPF 34 absorbs 97%. So don't pay extra for SPF 100. Just stick with something 15 or over.

The American Melanoma Foundation advises:

Choose a "broad-spectrum" sunscreen that protects against UVB and UVA radiation. PABA, or para-aminobenzoic acid, was one of the original ultraviolet B (UVB) protecting ingredients in sunscreens. However, some people's skin is sensitive to PABA, and it also can cause staining of clothing. Today, PABA has been refined and newer ingredients called PABA esters (such as glycerol PABA, padimate A and padimate O) can be found in sunscreens. PABA and PABA esters only protect against UVB radiation, the sun's burning rays that are the primary cause of sunburn and skin cancer. Also look for other UVB absorbers listed in the ingredients such as salicylates and cinnamates. You should look for a sunscreen that also protects against ultraviolet A (UVA) radiation, those rays that penetrate deeper into the skin and are the culprits in premature aging and wrinkling of the skin. UVA-screening chemicals include oxybensone, sulisobenzone and Parsol 1789, also called avobenzone.

They also point out that sunblocks containing zinc oxide and titanium dioxide can be helpful, though they are admittedly a bit messy.

Here's the Upshot

1. Avoid large doses of sunlight. Cancer can develop from a big dose of sun once in a while, or daily doses of sun.

2. You should put on sunscreen if you plan to be in the sun for 20 minutes or more. Seriously. No messing around. Pick a "broad spectrum" sunscreen that's SPF 15 or slightly higher.

3. Remember the UV index! You get more radiation during some parts of the day, and in some parts of the world (hello, New Zealand). Try to avoid sunlight at mid-day, or when your shadow is smallest.

4. Wear hats and protective clothing if you're going to be out in the sun for a long time. Try to stay in the shade when you can. Remember, limiting your dose of sunlight helps a lot. Be sure to take vitamin D supplements too, since your body needs the vitamin even if it doesn't need the sun.

5. And seriously, people, do not go to a tanning parlor or sit under sunlamps. Especially if you are under 30.

Now go forth, and frolic (safely) in the sun!

Photo by Ronald Sumners/Shutterstock

Essential Reading:

Ultraviolet Radiation: A Hazard to Children and Adolescents