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Skin and the aging process

It seems a paradox: The top layer of skin is replaced about once a month, so why does skin age? Part of the aging process is genetic. Just as your genetic makeup determines your eye color and whether your hair is curly or straight, genes also have some say in whether your skin retains a firm texture into your 60s and 70s, or begins to wrinkle and sag during your 40s. The breakdown of collagen and elastin that leads to droopy, lax skin occurs at different rates in different people.

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Chronological aging

Time takes its toll. As the years go by, skin undergoes a number of biochemical changes. Epidermal cells don't slough off as easily, and the supportive fibers of collagen and elastin break down. Skin doesn't retain as much moisture as it once did. The skin's ability to fight infection, feel sensations, and regulate body temperature also diminishes. Over several decades of sending instructions for new cell production, the DNA can become damaged and allow cells to grow out of control, with skin cancer as the result.

The deterioration of collagen and elastin and the pull of gravity can result in some of the classic signs of aging skin: fine lines around the eyes, deepened expression lines at the corners of the mouth and across the forehead, and sagging skin. The nails usually become more brittle, and hair may begin to thin.

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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.

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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).

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").

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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.

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Other sources of skin damage

In addition to the sun and the normal effects of aging, your skin can take a beating from many other sources.

Cigarettes. Cigarette smoking has long been recognized as a cause of wrinkles. Researchers haven't determined exactly how this happens, but they know that cigarette smoking damages the connective tissue, which is the basis for the skin's smooth appearance. Smoking-related wrinkles may not appear for a decade or more after the first puff, but damage occurs with every cigarette smoked. The combination of smoking and sun exposure is particularly toxic. Considering how harmful smoking is, not just to your skin but to every other part of your body, the healthiest choice is to avoid cigarettes. If you're trying to quit, support groups, nicotine gum and patches, and the drugs bupropion (Zyban) and varenicline (Chantix) can be useful smoking-cessation tools.

Irritants. Skin becomes thinner and doesn't heal as easily as you age, so take care in handling and working with irritants. Substances that are very acidic or alkaline can damage the skin's top layer and leave it susceptible to infection. You may encounter them in on-the-job exposures in industrial settings where solvents or cutting agents are used. Dusts, such as those from tobacco and wood, and gases, such as mace or tear gas, can damage skin, too. But if you wonder about the kind of irritation caused by vigorous scrubbing of your skin, you can rest easy. Scrubbing generally doesn't damage skin or cause wrinkles. If your skin is irritated by harsh chemicals, apply topical or oral corticosteroids followed by a nonirritating moisturizing cream to help the skin heal. Antibiotics may be needed if infection sets in.

Facial expressions. Laughter may be the best medicine, but it can add to creases and lines that develop through the years from repeated facial expressions. Every time you smile, squint, or frown, facial muscles contract and cause accordion-like lines and creases to form in your skin. Young skin bounces back. But as aging skin loses its elasticity and firmness, those lines and creases tend to become etched in the skin. Even sleeping with your face scrunched in a pillow at night may cause some lines to gradually appear.

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Review Date: 2007-03-01

Harvard Medical School does not endorse products or services.