How UV Rays Make Your Skin Tan

woman in bikini applying sunscreen lotion at a tropical beach
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Many people want a tan, but do you know how skin tans? A great amount of money, time and effort goes into getting, and keeping tanned skin. Our teens are often preoccupied with having a “perfect” and even tan. But how does it happen?

Ultraviolet Rays

Our sun produces three main types of ultraviolet rays: UVA, UVB, and UVC. UVC rays are caught by our ozone layer and don't play a factor in tanning. Most, but not all, of UVB rays are also caught in the ozone layer, so some UVB rays play a factor in tanning. When we are talking about tanning by the sun's ultraviolet rays, UVA and some UVB rays are what causes the tan.

Ultraviolet rays are not created equally. UVA rays and UVB rays have different wavelengths, allowing the rays to penetrate different layers of the skin. UVB rays have short wavelengths and penetrate the outermost layers of the skin (the epidermis). UVA rays have longer wavelengths and can penetrate deeper than UVBs, right into the dermis, the middle layer of the skin.

How UV Rays Cause a Tan

UV rays cause tanning by the way they affect the melanin in our skin. Melanin is a pigment in our skin produced by cells called melanocytes and is what gives our skin its color.

  • UVA causes a tan by oxidating the melanin. Essentially, the melanin undergoes a chemical reaction after being exposed to UVA, causing it to become darker. When the melanin looks darker, the skin itself looks tanned and dark.
  • UVB causes a tan by a different method. UVB causes an increase in the production of melanin in the skin and other changes to the cells that the melanin is stored in. These UVB effects cause the skin to become darker or tanned.

What About Tanning Beds?

Tanning beds and tanning lights used to be thought to be a safe alternative to tanning outside, but those claims are absolutely not true. Older tanning beds used to produce UVB waves that caused more burning, so these beds were changed to use UVA waves. These waves don't burn the skin the same way that UVB waves burn, but that does not mean they are safe. UVA waves are thought to cause skin cancer and immune system issues. If you have ever seen someone who has tanned extensively throughout their lifetime, you can see that the UVA waves damage the skin in a way that promotes deep wrinkling.

Damaging Effects of UV Rays

Both UVA and UVB rays can cause skin damage, but just like how they differ in how they cause the appearance of a tan, they differ in their ability to damage the skin. As noted with the information on tanning beds, it was once thought that UVB rays were the most dangerous. We are learning, however, that UVA can be every bit or more dangerous, as they penetrate the skin more deeply.

Sunscreen and UV Rays

Knowing that both UVA and UVB rays can be dangerous, it's important to select a sunscreen which covers both of these exposures. Many sunscreens don't cover UVA rays. Make sure to learn about sunscreen ingredients which protect against UVA rays, as many products do not. After you have found a product which will defend against UVA rays, check out the pros and cons of ingredients which block UVB rays.

You may wonder why you need to do this research in selecting a sunscreen for your teen, and this is an important point. There are not currently any regulations in place which help parents know which sunscreens are good and will give their child the coverage she needs. Until we know more, the Environmental Working Group has put together a sunscreen guide that can do some of the legwork for you as you try to navigate your way through the multitude of products available.

Vitamin D and UV Rays

As with so many things in medicine, we're learning that while the sun can cause skin damage leading to premature wrinkling and skin cancer, there are also some benefits of time in the sun.

Wearing sunscreen may help to prevent skin cancer, but on the downside, may result in vitamin D deficiency. Vitamin D deficiency, in turn, is linked with many diseases ranging from several cancers to multiple sclerosis to depression.

What are the sources of vitamin D? One of the primary ways our bodies obtain vitamin D is through absorption from sun exposure. You may think of dietary sources, but this is hard with the average diet. The recommended daily allowance for Vitamin D is 600 IU. A glass of milk contains around 120 IUs. Supplements are available as well. In contrast, spending 10 to 15 minutes in the sun without sunscreen on a summer day in light clothing may result in the absorption of 5,000 IU's.

Since the majority of Americans have lower than recommended vitamin D levels, many of the dermatology organizations are now reconsidering their previous sunscreen recommendations to perhaps include a short period of time in the sun before application of sunscreen. If you are worried about your teen, a simple blood test can determine where her level is at, and your pediatrician can help you decide if a supplement or some time in the sun is needed. In addition, keep your eyes out for dermatology recommendations regarding healthy sun exposure which may be changing.

Bottom Line on Skin Tans

UVA and UVB rays, from the sun or from a tanning bed, are what causes the skin to tan. There are risks to tanning, and it is important to discuss your concerns with your teen. In fact, discussing the risks and benefits of sun exposure are a good way to discuss the importance of moderation in many activities in their lives.

5 Sources
Verywell Family uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. U.S. Food and Drug Administration. Consumer updates. Indoor tanning: the risks of ultraviolet rays.

  2. U.S. Food and Drug Administration. Sunscreen: how to help protect your skin from the sun.

  3. Environmental Working Group. EWG's guide to suncreens.

  4. Wimalawansa SJ. Prevention of chronic diseases by maintaining physiological concentrations of vitamin D. J Clin Endocrin Diabe Rese. 2019;1(1):001.

  5. U.S. Department of Health and Human Services, National Institutes of Health, Office of Dietary Supplements. Vitamin D fact sheet for health professionals.

Additional Reading

By Barbara Poncelet
 Barbara Poncelet, CRNP, is a certified pediatric nurse practitioner specializing in teen health.