Q. Why do I need sunscreen year-round?

A. The sun produces visible and invisible rays. The rays you can't see are known as ultraviolet A (UVA), ultraviolet B (UVB) and ultraviolet C (UVC). These rays are dangerous to your skin and can cause suntan, sunburn and skin damage.

The sun emits UV rays all the time. It's not heat that causes damage, it's ultraviolet light. UV rays may still be strong on cold or overcast days and can penetrate through cloud cover, fog and haze. Things that can increase the amount of UV light you are getting are:

• Summer

• Time of day (10 a.m.-3 p.m.)

• High altitudes

• Proximity of the equator

• Wind

• Reflected rays from water, sand or snow.

• Some medications

Besides damaging your skin, ultraviolet light damages the body's ability to fight off skin cancer using the defenses of the immune system. This is one of the most important reasons that sunscreens are necessary as you get older.

Tanning salons use ultraviolet light and have the same effects as the sun -- including more rapid aging and increased chance of melanoma and skin cancer. No kind of ultraviolet light is safe!

The best way to reduce UV exposure and its damage is daily application of sunscreen. Most people apply sunscreen only before outdoor activities. However, more than half of ultraviolet light exposure occurs in non-summer months and during routine daily activities. It's never too late to start: a person who begins using SPF-15 sunscreen daily at age 40 can reduce lifetime exposure by 40 percent.

No matter how dark your skin is, you're still at risk. The skin produces a substance called melanin. When UV rays enter the skin, the skin protects itself by making more melanin, causing a tan. The more melanin in your skin, the more protected you are from ultraviolet light. However, it is only equal to a sunscreen with an SPF of 2 or 4. That is not very good protection and is not a substitute for sunscreen.

If you want to add color to your skin, the self-tanning creams, lotions and sprays are safe and effective. Spray-on tans are also safe. However, the color does not protect you from sunburn, and sunscreen must still be used.

JOHN ZITELLI, M.D.
Dermatology