We couldn't do without the sun. It keeps us warm, fuels photosynthesis so we have spinach to eat and helps our bodies make vitamin D. We couldn't see across the street without the sun.

But it also has a dark side. If we fly too close to Old Sol, for too long, on a beach, pool or tennis court, its UVB rays penetrate the top layers of our skin, causing sunburn. Its longer UVA rays penetrate the dermis, the next layer down, causing wrinkles, age spots and, too often, skin cancer.

Do we even dare sunbathe these days? We asked the experts.

SUNSCREENS AND SPF

Q: Will sunscreens protect me?

A: They can help, the FDA says. But take their label claims with a large grain of salt. The FDA has been trying since 1999 to get sunscreen makers to stop using what it calls 'unsupported, absolute and/or misleading and confusing terms such as `sunblock,' 'waterproof' '' and others. Some brands say ''waterproof'' on their front label even though their back labels say, ''Rinse with water to remove.'' So don't count on ''sunblock'' to block the sun, and don't count on ''waterproof'' products to stay on in the water. Be sure to reapply often.

Q: What SPF should I use?

A: You need an SPF (sun protection factor) of at least 15, according to the Skin Cancer Foundation. Dr. Jonette Keri, a dermatologist at the University of Miami Miller School of Medicine, recommends an SPF of at least 30 if you're at the beach, pool or tennis court. ''Most people don't put on enough,'' she says. It takes two shot glasses of lotion to cover the average bather, and most people put on only about half that amount. So the higher SPF can help. ''The higher the better,'' she says.

Q: Is SPF the only factor I should consider?

A: No. An SPF rating measures a sunscreen's protection against UVB (ultraviolet B) rays but not against UVA (ultraviolet A) rays, which can also cause wrinkles and skin cancer. For UVA ray protection, check the sunscreen label for the ingredient avobenzone or mexoryl.

Q: When should I apply sunscreen?

A: Apply 30 minutes before getting into the sun so your skin can soak up your sunscreen, and reapply every 90 minutes -- more often if you go in the water, sweat a lot or towel off.

Q: Can I put sunscreen on my baby?

A: Sunscreen is OK after about 6 months of age, Keri says. Still, keep Snookums out of the sun as much as possible, and re-apply often.

Q: What about younger than 6 months?

A: If you must take an infant to the beach, keep him or her in a stroller and use a ''baby sun protective cover'' with a UPF (ultraviolet protection factor) rating.

AT THE BEACH

Q: Is it safe to go to the beach?

A: ''I want my patients to have fun and go to the beach, but they should protect themselves as much as they can,'' says Keri. Wear sunscreen when you go in the water. When you get out, get under an umbrella.

Q: I can't lie out in the sun with my trashy novel?

''I don't want you to do that,'' says Keri. ``People have in mind that a tan is healthy. It's not. We [dermatologists] are trying to change the culture -- get people not to go out and lie in the sun to get a tan. We know a lot more about ultraviolet radiation than we used to. I think most of my colleagues would agree.''

Q: Can I hit the beach at any time of day?

A: Seek shade between 10 a.m. and 4 p.m., the Skin Cancer Foundation says.

Q: Is it safe to lie under a beach umbrella?

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