Photoaging - Skin And The Aging Process: Skin Health

Content provided by the Faculty of the Harvard Medical School

Photoaging

The single biggest cause of damage to skin as you age is not aging itself — it's sun exposure. This damage is called photoaging. Over the years, sun exposure causes fine and coarse wrinkles; baggy skin with a yellow, leathery appearance; and dry, scaly skin. It also increases the risk for skin cancer. Because sun exposure diminishes collagen, which supports a network of blood vessels, photoaging can cause skin to bruise more easily.

You can easily distinguish the effects of photoaging from those of chronological aging. Look at the lines and pigmentation of the skin on your face and the back of your hands; feel its texture. Now do the same on a part of your body that hasn't received much sun exposure, such as your lower abdomen or buttocks. The difference can be great, especially if you've been a sun worshipper throughout your life. People are spending billions of dollars annually to try to counteract the effects of photoaging (see "Skin rejuvenation procedures").

Skin damage from sun exposure is caused by ultraviolet (UV) radiation. Not all the sun's rays are created equal. Some wavelengths of UV radiation penetrate the skin more deeply than others. Realizing this difference has prompted researchers to question whether some types of UV rays mainly cause wrinkles and the brown spots (sometimes called "age spots" or "liver spots") while others speed the development of skin cancer.

Three types of UV radiation

The wavelengths of UV radiation fall between those of visible light and x-rays. The sun's UV radiation reaches the earth in three main wavelengths (see Figure 2).

Figure 2: Three wavelengths of skin damage Three different wavelengths of ultraviolet (UV) light come from the sun. UVA is the longest wavelength and penetrates most deeply. UVB is the next longest and causes burns to the skin's upper layer. UVC, the shortest wavelength, normally is blocked by the ozone layer in the atmosphere. Which type causes the most damage? No one knows for sure. That's why the most effective protection is to stay out of the sun or wear protective clothing.

UVC. This wavelength is the shortest of the three. It also has the highest energy level and is the most damaging. UVC rays are capable of destroying the skin, but they're usually absorbed in the atmosphere by the ozone layer before they reach the earth's surface. However, in places such as Australia, where scientists suspect the ozone layer is thinning, UVC rays pose a risk for very serious skin damage.

UVB. These rays are slightly longer and lower in energy than UVC rays, so they're less damaging to skin. UVB rays penetrate the epidermis, and the visible result of their damage is a sunburn. Experts generally believe that the more often you've been sunburned, the more likely you are to develop skin cancer. Research suggests that UVB rays cause a distinctive genetic mutation that permits unabated cell growth, giving rise to cancer. In fact, more than 90% of squamous cell cancers have this specific mutation.

UVA. The rays with the longest range of wavelengths, called UVA, also play a role in photoaging and in the development of skin cancer. Because of their longer wavelength, these rays penetrate more deeply into the dermis. Only about 10% of UVB rays reach the dermis, but researchers believe that 50% of UVA rays do so. And when you're in the sun, you're exposed to more UVA: The sunlight that reaches the earth contains about 10 times as much UVA as UVB (see "Don't get burned by improper sunscreen use").

Risks of UV exposure

If you're taking certain medications, sun exposure can cause additional damage to your skin. Such drugs, called photosensitizers, increase your sensitivity to UV radiation. Reactions include overly reddened skin, hives, swelling, and itchy, scaly skin. Cataracts and damage to blood vessels or the immune system also may occur.

Some of these drugs are more commonly taken by people as they get older — for example, antiarrhythmics, such as amiodarone, and diuretics, including hydrochlorothiazide. Some antibiotics, such as doxycycline, can also cause photosensitivity. It's important to check with your doctor to determine whether any of the medications you're taking could cause photosensitivity.

A less common cause of skin damage is exposure to infrared radiation (heat). It's not a major cause of skin damage, but researchers believe that it may add to the effects of UV rays. Some exposures may occur on the job — think of the short-order cook who stands in front of infrared heat lamps all day. Infrared heat lamps also are used to heal some muscle injuries or to relieve pain and stiffness from osteoarthritis.

Last updated:	July 20, 2007