Sun Protection Factor (SPF)

How should sunscreen be used?
Who should wear sunglasses?

Sun protection factor is a standard measurement of a sunscreen's ability to protect the skin and to prevent sunburn. The SPF scale for rating sunscreens ranges from 2 to 52 and simply describes the amount of time of sun exposure before skin burns. For instance, an SPF4 means the skin can be exposed to the sun 4 times longer than unprotected skin without burning. The actual amount of time that a sunscreen protects depends on the skin type. If a person normally burns in 10 minutes, an SPF2 would theoretically protect that person from burning for 20 minutes. If a person would ordinarily burn in 60 minutes, an SPF2 would protect him or her for 2 hours.

Sunburn and damage to the skin is caused by exposure to ultraviolet rays from the sun. Ultraviolet radiation is divided into three components: UV-A, UV-B, and UV-C. Because most UV-C radiation is absorbed by the earth's atmosphere, it's the UV-A and UV-B rays that are of concern when protecting the skin. UV-B rays are partially absorbed by the earth's ozone layer, but UV-A radiation is not stopped by ozone.

UV-A rays that cause tanning and are thought to contribute to the aging of skin, while UV-B causes most sunburn. Overexposure to either UV-A or UV-B radiation can cause skin cancer. UV-B rays are stronger during the summer months, while UV-A radiation is prevalent year round. Ultraviolet rays are stronger near the equator and at higher elevations where the atmosphere is thinner.

How should a sunscreen be used?

Sunscreen products are regulated by the FDA and come in a variety of forms, including alcohol-based lotions and gels, creams, sticks, and sprays. The alcohol-based products are better for oily skin, while the creamy lotions and sprays are the easiest to apply. The sticks are good for noses, lips, and around the eyes.

No sunscreen can provide total protection from ultraviolet rays, but those rated SPF15 or higher screen out a large percentage of UV-B rays and are recommended by most doctors. Individuals with fair skin or with a history of skin cancer in the family should use a sunscreen that is rated even higher or may want to use a sun block for total protection.

Uneven application, swimming, sweating, and rubbing off reduce the effectiveness of sunscreens, and the sunscreen should be reapplied every two hours to ensure the best protection. Staying inside during peak hours (10 a.m. to 3 p.m.) is the best way to avoid exposure to excessive ultraviolet radiation. In addition to using sunscreen products, wear wide-brimmed hats, UV-protective sunglasses, and dark, tightly woven clothing for added protection from harmful UV rays. Remember, reflective rays from snow, water, sand, and concrete can also cause sunburn. Use sunscreen even when you're under a beach umbrella because the sun's rays reflect off the surrounding sand.

Because sunburns on young skin cause wrinkles and skin cancer in later years, babies and children need special protection from the sun. At least 15 minutes before children are going to spend time outdoors, apply a sunscreen with an SPF of at least 15. A child's sensitive skin can burn even on a cloudy day because 80 percent of the sun's rays can penetrate light clouds, mist, and fog.

Some people are allergic to certain sunscreen products and may develop rashes or dermatitis. These reactions may be caused by a chemical used in the sunscreen, or by a fragrance or preservative. If changing the brand of sunscreen doesn't help, see a dermatologist.

If you are going to spend time in the sun, be aware that some medications, such as antibiotics, blood pressure medications, and antihistamines, as well as some perfumes and alcohol, may cause your skin to be more sensitive to the sun. Talk to a doctor or pharmacist to determine if special sun safety precautions are necessary.

Who should wear sunglasses?

Overexposure to either UV-A or UV-B radiation can cause eye damage as well as skin cancer. Most UV-B rays are absorbed by the cornea and the lens in the front part of the eye, and do not penetrate to the retina in the back of the eye. It's these rays that cause alterations to the eye's natural lens and may cause cataracts. UV-A radiation, although lower in energy, can penetrate more deeply into the eye, causing damage to the retina and leading to conditions such as macular degeneration, a leading cause of blindness.

Adults, as well as children, should wear sunglasses with UV-A/UV-B protective lenses. Sunglasses should not only filter visible light but also be labeled as protecting the eyes from at least 99 percent of ultraviolet rays. Wraparound sunglasses help minimize the amount of harmful sunlight that enters the eyes. Even infants and small children should wear sunglasses when in the sun.