When it comes to skin cancer and the sun, most people are still in the dark. Sure, we all know we're. supposed to use sunscreen, but how much are you supposed to use? Is that white T-shirt really protecting your skin? And does it matter that you can't put sunscreen on your eyelids? The wrong answers can be costly. The sun's harmful rays can cause painful burns, premature aging and wrinkles, skin cancers and serious eye disease. Sunshine contributes to one million new cancers each year, affecting about one in every 70 people. So here's a look at everything you need to know about sun protection, but didn't know you were supposed to ask.

Understanding SPF. Many people think a high SPF - or sun: protection factor -- guarantees protection. But the SPF is simply an indicator of how long you can stay in the sun before burning. If you would normally burn after 10 minutes in the sun without :sunscreen, then 15 SPF sunscreen theoretically would allow you to stay outside for about 2 1/2 hours without turning red.
But the SPF rating is based on lab tests. In the real world, a number of factors, including how much sunscreen you applied, how much you sweat and I whether you swim, will affect the level of protection you really get. That's why you should re-apply sunscreen at least every two hours, regardless of the rating. And be warned: Once you've reached the time allotted by your SPF, adding more sunscreen, won't buy you more time because you've already maxed out your skin for the day. More important, an SPF rating applies to the shorter
UVB rays. UVA rays penetrate more deeply and are believed to play a significant role in the development of melanoma. It's known that people who use tanning booths, which use UV'A rays, are two to three times more likely to get skin cancer.
So look for a sunscreen that offers "broad, spectrum" protection and check the ingredients for Parsol 1789, a]so called avobenzone, or butyl methoxydibenzoylmethane, which many doctors say is the best UVA blocker available. Sun screens in other countries have an even better blocker, Mexoryl, which hasn't yet been approved in the Unites States.

An ounce of prevention. The biggest mistake people make is not using enough sunscreen. You should slather on at least an ounce which is-about enough sunscreen to fill a shot glass. That means people who spend a lot of time outside should go through several bottles a summer.
If you don't use enough sunscreen, then you are getting far less sun protection than is printed on the bottle. For instance, a person who skimps on 30 sun block may only be getting the benefit of a 10 or 15.
Don't neglect areas that don't normally burn. Deborah Schwartz, 50 years old, of Westbury, says she always focused on her face, shoulders and back when
applying sunscreen, but a small spot on the under- side of her forearm turned out to be early-stage melanoma.
"I don't remember ever getting a burn under my arm - it wasn't a danger spot," she says. "Now I've learned you can't miss anything."
And remember to wear sunscreen even for short periods of exposure. "If you get just 15 minutes a day and you do it four days in a row, it's the. same as being out in the sun an hour" says Ted Daly, dermatologist at Nassau University Medical Center in East Meadow.

The role of clothes. Clothing helps, but not as much as you think. Many people throw on a T-shirt to protect their skin from the sun. But as the Harvard Health Letter recently noted, a white T-shirt has an SPF of only 5, and it. offers even less protection when wet. The looser the weave and lighter the color, the less protection.
A Swedish study published in the Archives of Dermatology last week notes an alarming rise in skin cancers in places normally covered by clothes. To be safe, especially with children, slather the entire body . with sunscreen, even those parts. that will be under. clothing. Some. people buy special clothing, such as that made by Solunibra, that offers additional SPF protection.

What makes your skin more vulnerable. Certain medications and lotions will make your skin burn more easily than usual. Products with alpha-hydroxy acids may increase risk, as will some antihistamines, anti-inflammatory drugs, antibiotics, aritidepressants, cardiovascular drugs and diuretics.

Sunscreen for the eyes. Few people think about eye protection. But basal and squamous cell carcinomas, two types of skin cancer, are fairly common on eyelids, and about 2 percent of all cancers are in the eye. Sun damage while young increases risk for cataracts, age-related blindness and other eye diseases. People with light-colored eyes are at highest risk, as are people who work outside or are regularly exposed to sun glare, such as fishermen and ski instructors.
Cheap sunglasses do more harm than good because they cause the eye to dilate but offer no UV protection. Look for sunglasses that block at least 98 percent of harmful rays: It should say so on the sticker