Everyone needs a little sunshine. About 15 minutes of exposure a day helps the body make Vitamin D, which is important for healthy bones and teeth. But longer exposure may cause many problems, from wrinkles to skin cancer. One particularly deadly form of skin cancer, malignant melanoma, has been on the rise in recent decades, as tanning has become more popular. Over the same period, scientists have warned that the thin layer of ozone that protects life on Earth from the sun's ultraviolet (UV) radiation is being depleted. This allows more UV radiation to get through, adding to the risk of overexposure.

Sunscreens help protect against the sun's damaging effects. But just how much protection they provide is a matter of debate. The sun gives off two kinds of ultraviolet radiation, called UV-A and UV-B. For many years, experts thought that only UV-B was harmful. However, recent research suggests that UV-A may be just as dangerous as UV-B, although its effects may take longer to show up. In particular, UV-A may have a role in causing melanoma. Most sunscreen products contain ingredients that provide adequate protection only against UV-B rays. Even those labeled as broad-spectrum sunscreens may offer only partial protection against UV-A radiation. Those containing the ingredient avobenzone give the most protection against UV-A rays.

Some medical experts are concerned that sunscreens give people a false sense of security, allowing them to stay in the sun longer than they should. Although sunscreens protect the skin from burning, they may not protect against other kinds of damage. A number of studies suggest that people who use sunscreens may actually increase their risk of melanoma because they spend too much time in the sun. This does not mean that people should stop using sunscreens. It means that they should not rely on sunscreens alone for protection. According to the American Academy of Dermatology, sunscreens should be one part of sun protection, along with wide-brimmed hats and tightly-woven clothing that covers the arms and legs.

Sunscreens are also recommended for patients with rosacea or other skin disorders that are aggravated by exposure to sunlight.

Many brands of sunscreens are available, containing a variety of ingredients. The active ingredients work by absorbing, reflecting, or scattering some or all of the sun's rays. Most sunscreen products contain combinations of ingredients.

The U.S. Food and Drug Administration (FDA) has required sunscreen products to carry a sun protection factor (SPF) rating on their labels since 1999. This number tells the consumer how well the sunscreen protects against burning. The higher the number, the longer a person can stay in the sun without burning.

Sunscreens are usually grouped into two major categories, namely chemical absorbers and physical blockers. Chemical absorbers absorb high-intensity UV rays while physical blockers reflect or scatter them. Chemical absorber compounds include avobenzone, padimate O, octyl methoxycinnamate, octisalate, and octocrylene. Physical blocker compounds include titanium dioxide and zinc oxide. The chief drawback of the physical blockers is their tendency to leave a white film on the skin, causing many people to use less of the product than they should for full sun protection.

A plant-derived compound that shows promise as a sunscreen is nobiletin, a flavonoid extracted from Citrus depressa or flat orange, a small citrus fruit native to Taiwan and Okinawa. Topical application of nobiletin has been shown to be effective in preventing the swelling and reddening of the skin associated with overexposure to sunlight.

Sunscreen products are sold as lotions, creams, gels, oils, sprays, sticks, and lip balms, and can be bought without a physician's prescription.

One should be sure to read the instructions that come with the product. Some need to be applied as long as one or two hours before sun exposure. Others should be applied 15–30 minutes before exposure, and reapplied frequently during exposure.

People should apply sunscreen liberally to all exposed parts of the skin, including the hands, feet, nose, ears, neck, scalp (if the hair is thin or very short), and eyelids. They should take care not to get sunscreen in the eyes, as it can cause irritation. People should also use a lip balm containing sunscreen to protect the lips, and reapply sunscreen liberally every 1–2 hours—more frequently when perspiring heavily or after swimming.

Sunscreen alone will not provide full protection from the sun. When possible, one should wear a hat, long pants, long-sleeved shirts or blouses, and sunglasses. Try to stay out of the sun between 10 A.M. and 2 P.M. (11 A.M. to 3 P.M. Daylight Saving Time), when the sun's rays are strongest. The sun can damage the skin even on cloudy days, so get in the habit of using a sunscreen every day. Be especially careful at high elevations or in areas with surfaces that reflect the sun's rays, such as sand, water, concrete, or snow.

Sunlamps, tanning beds, and tanning booths were once thought to be safer than the sun, because they give off mainly UV-A rays. However, UV-A rays are now known to cause serious skin damage and may increase the risk of melanoma. Heatlh experts advise people not to use these tanning devices.

People with fair skin, blond, red or light-brown hair, and blue or light-colored eyes are at greatest risk for developing skin cancer. So are people with many large skin moles. These people should avoid exposure to the sun as much as possible. However, even dark-skinned people, including African Americans and Hispanic Americans may suffer skin damage from the sun and should be careful about exposure.

Other groups of people who should minimize sun exposure are those who have had organ transplants or recent plastic surgery. Patients who have received organ transplants have a greatly increased risk of developing skin cancer, and the facial skin of people who have had face lifts or similar plastic surgery procedures sunburns more easily than intact skin.

Sunscreens should not be used on infants under 6 months of age because of the risk of side effects. Instead, children this young should be kept out of the sun. Children over 6 months should be protected with clothing and sunscreens of at least SPF 15, preferably lotions. Sunscreens containing alcohol should not be used on children because they may irritate the skin.

Older people who stay out of the sun and use sunscreens may not produce enough vitamin D in their bodies. They may need to increase the vitamin D in their diets by including foods such as fortified milk and salmon. A health care professional can help decide if this precaution is necessary.

Anyone who has had unusual reactions to any sunscreen ingredients in the past should check with a physician or pharmacist before using a sunscreen. The physician or pharmacist should also be told about any allergies to foods, dyes, preservatives, or other substances, especially the following:

• artificial sweeteners
• such anesthetics as benzocaine, procaine, or tetracaine
• diabetes medicine taken by mouth
• hair dyes
• sulfa medicines
• water pills
• cinnamon flavoring

People with skin conditions or diseases should check with their physicians before using a sunscreen. This is especially true of people with conditions that get worse with exposure to light.

The most common side effects are drying or tightening of the skin. This problem does not need medical attention unless it does not improve.

Other side effects are rare, but possible. If any of the following symptoms occur, check with a physician as soon as possible:

• acne
• burning, itching, or stinging of the skin
• redness or swelling of the skin
• rash, with or without blisters that ooze and become crusted
• pain in hairy parts of body
• pus in hair follicles

Anyone who is using a prescription or nonprescription (over-the-counter) drug that is applied to the skin should check with a physician before using a sunscreen.