Being in the sun certainly feels good, but make sure you are protecting your skin against its devastating effects

Too much sun is simply perilous to skin, so it's important to protect your precious skin from damaging exposure. Don't think that you're OK because it's winter or the sun isn't out in full force - you're in danger even under these conditions.

Here we review just why the sun can be so damaging to your skin - from producing brown spots to causing wrinkles - and how to protect yourself with a sunscreen selected for your type of skin.

What causes sunburn and skin damage?
There are two kinds of ultraviolet rays that reach the earth's surface: ultraviolet A (UVA) and ultraviolet B (UVB). UVB rays cause your skin to show the signs of sunburn, but most sunscreens protect against them. These rays are also partially screened out by the ozone layer, an invisible shield that protects us from the sun. But over the years the ozone layer has become thinner, so we're getting more exposure.

UVA rays don't burn your skin, but they do contribute the most damage. They penetrate your skin more deeply and affect the cells on a molecular level. That's why it's important to look for a sunscreen that will protect you from both UVA and UVB rays. UVA damage results not only in wrinkles and sagging skin, but can also cause skin cancer. And UVA intensifies with altitude, so it's particularly important to protect yourself when skiing or mountain climbing.

Selecting a sunscreen
The best protection from the sun is to stay out of it. But there are ways to protect yourself when you can't avoid exposure. Sunscreens must be part of your daily regimen. They're available under a bevy of cosmetic labels and offered in the form of lotions, creams, gels, sprays and oils. A good sunscreen absorbs and/or blocks ultraviolet rays; make sure the one you choose is effective against both UVB and UVA. (Look for the ingredients parsol 1789 or zinc oxide.) Scientists used to believe that it was only UVB rays that caused skin cancer, but they now know that UVA rays are, in fact, more dangerous.

When choosing a sunscreen or sunblock you'll notice an SPF (sun protection factor) number. The SPF indicates the amount of exposure your skin can handle from UVB rays before turning red. Dermatologists recommend an SPF of at least 15 for all skin types. To work out how long it will take you to develop a sunburn, multiply the SPF number by 10; for example, someone with medium skin using SPF 15 should be able to stay outside for 150 minutes before burning.

Even with a protective sunscreen, you need to use common sense about how long you stay in the sun. Improved sunscreens have encouraged people to stay out in the sun for greater periods of time, but dermatologists stress that no matter what strength sunscreen you use, you'll still get some exposure. And if the product you've selected has only UVB protection, you're at risk for the most serious kinds of skin damage, including skin cancer. In fact, in recent years there seems to have been an increased incidence of skin cancers; doctors theorize it's because more people are using UVB protection only and remaining in the sun longer.

How to use a sunscreen
For optimal protection, generously apply a generous amount of sunscreen over all parts of your body that will be exposed to the sun - the mistake many people make is not applying enough. Let it absorb for at least 15 minutes before going outdoors. Bear in mind that some people are allergic to certain ingredients found in some sunscreens, so it's a good idea to test the product first on a small portion of your skin. (It's not advisable to test it on your face.)

Although some sunscreens claim to be water-repellent or waterproof, you should still reapply every two hours. If you go into the water or participate in any activity that causes you to sweat excessively, you should reapply sunscreen immediately after drying off. Nowadays, many makeup foundations contain a sunscreen of SPF 15; this can protect you during the day. Lips also need to be protected from the sun; many lip balms have an SPF of 15 or higher.

Which SPF is right for you?
Here's an idea of what level of protection you should use, according to skin type: