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How Ultraviolet Light Affects Your Skin

May 11, 2017

Ultraviolet (UV) light makes up just a small portion of the sun’s rays, but it is the primary cause of skin damage. Exposure to UV light causes damage to DNA in skin cells, increases the risk of skin cancer and accelerates signs of aging such as fine lines, deep wrinkles and dark spots.

There are three types of UV light: UVA, UVB and UVC. Let’s look at their differences and how they affect the appearance and health of your skin.

UVA Light

UVA light is not absorbed by the ozone layer and is able to penetrate the dermis in humans, which is the deepest layer of skin. UVA rays cause many effects on the skin including immediate skin redness and darkness, formation of fine lines, wrinkles and age spots. UVA also plays a minor role in the development of skin cancer because it causes formation of free radicals in the skin.

UVA radiation is able to penetrate glass (windows), which is why doctors and dermatologists recommend wearing sunscreen on a daily basis, even if you don’t go outdoors.  A great example of the advanced skin aging that can be seen with daily exposure to UVA can be seen in the photo below, originally published in the New England Journal of Medicine.  

The man in this photo was a truck driver for 25 years, so that the left side of his face received significantly more sun exposure and UVA rays than the right side. You can see the dramatic difference, as the left side of his face has less elasticity, more sagging, thicker skin and deeper wrinkles.

Remember, UVA = Aging!

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 Photo: Huffington Post/NEJM

UVB Light

UVB is another form of UV light. Unlike UVA rays, not all UVB reaches the earth because some rays are absorbed by the ozone layer. Because UVB rays are shorter and have a higher frequency, they are more damaging to skin as they penetrate the epidermis (top layer of skin).

UVB radiation causes sunburns and delayed tanning. It plays a major role in the development of all types of skin cancers causing DNA damage to skin cells and the immune system. UVB is also important in the synthesis of Vitamin D3.

Remember, UVB = Bad Burns!

UVC Light

UVC rays are too short to get through the Earth’s atmosphere. Although UVC is the most dangerous form of UV radiation, it is completely absorbed by the ozone layer and does not normally cause skin cancer.

Of course, the amount of UV light on skin at any given time and place is dependent on many factors including the time of day, time of the year, elevation and cloud cover.

You can refer to the UV Index, which ranges from 1 to 11+, to see how intense the UV light is in the area. A higher number means greater exposure of UV rays and a higher risk of sunburn and skin damage. 

What’s the Difference Between a Tanning Booth and Phototherapy Treatment?

Because of the dangers of UV light, dermatologists are emphatic about avoiding outdoor sun exposure, protecting your skin with sunscreen, and avoiding tanning booths at all costs.

But my patients sometimes ask me, “Why shouldn’t I use a tanning booth if you have a tanning booth in your office?” While it may look very similar to a tanning booth, it's actually a phototherapy booth, which has very different effects. Here are the facts:

Tanning booths:

  • Most tanning booths give off primarily UVA rays.
  • 20 minutes spent in an indoor tanning booth equals about 2-3 hours in the noontime sun.
  • People who first use a tanning bed before age 35 increase their risk for melanoma by 75%.
  • People who use tanning beds are 2.5 times more likely to develop squamous cell carcinoma and 1.5 times more likely to develop basal cell carcinoma.
  • The Federal Trade Commission has ruled against claiming health benefits for indoor tanning.

Phototherapy booths:

  • Phototherapy is light therapy that is prescribed and administered by a dermatologist in their office. Treatment involves exposing the skin to an artificial UV light source for a set length of time on a regular schedule.
  • Nowadays, the most common type of phototherapy used is called narrowband UVB. Narrowband refers to a specific wavelength of UV radiation that is safe for the skin.
  • Narrowband UVB has anti-inflammatory effects on the skin and is used to treat many skin conditions such as psoriasis, eczema, vitiligo and even some types of skin lymphomas. There is no evidence to suggest that broadband or narrowband UVB treatments increase the risk of skin cancer.

What About Vitamin D?

While it is true that exposure to sunlight (specifically UVB) helps to produce Vitamin D3 in your body, the amount of sunlight that you actually need for adequate levels of Vitamin D is minimal. About five to ten minutes of exposure to the arms and legs, or hands, arms and face, two to three times per week is sufficient for healthy Vitamin D levels.

This is especially true if you eat foods that are high in Vitamin D, such as fish, mushrooms, soy, dairy and eggs or take oral Vitamin D supplements. Because it is not uncommon for some people to have low Vitamin D levels, especially in areas of the country that tend to be overcast during most of the year, most physicians now recommend daily oral supplementation.

This is especially important for women who are at increased risk of developing osteomalacia or osteoporosis. Currently the recommended dose of Vitamin D for the general population is 600 IU for those 1-70 years of age and pregnant or breastfeeding women, and 800 IU for those over 71 years of age.

What Can I Do to Protect Myself?

The lesson to learn here is that sunlight is not the enemy, but rather the conduit of unavoidable UV radiation exposure that we must learn to control.  Many people love being active outdoors on a nice, sunny afternoon.

On days such as these when we venture out to enjoy nature, we can protect our skin by:

  • Lingering in shaded areas
  • Wearing sunscreen on exposed areas of the skin (minimum SPF of 30, reapplying every 1-2 hours)
  • Wearing photoprotective clothing (wide brimmed hats, sunglasses, breathable long sleeved shirts, etc).

For everyday protection, use a moisturizer with sunscreen on your face, neck and chest. Minimizing exposure to UV radiation through these measures is one of the best things you can do for your skin in order to decelerate the signs of aging and prevent skin cancer.

Topics: Skin Cancer, ultraviolet light

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