New York ? Skin does a good job of protecting you against the cold, windy dry air that blows all winter long, but like any barrier that takes a constant beating, skin needs to be cared for and treated with the proper materials.

You waterproof your boots and Armor All your car, right?

The season’s extremes are the enemy of skin, says Dr. Doris Day, a Manhattan dermatologist.

“In the winter, you tend to have very cold windy conditions outside and then you go inside into hot and dry conditions. It’s terrible for the skin, and it acerbates redness and dryness,” explains Day, who is a consultant for Good Skin Skincare for Kohl’s. “Then you take a scalding hot shower to warm you up and that messes up things further. Hot water takes the natural oil out of the skin even more and opens up the pores.”

Because skin is a fairly resilient organ, it gives up a lot of its blood supply to help keep other vital organs warm, Day says. But the back-and-forth from cold to hot can take its toll if the skin is overloaded by the return of the blood and the superficial blood vessels dilate when you go inside. “This can burn, cause deep redness and there’ll be a sensitivity to the skin.”

“Your skin, like your other organs, likes consistency and continuity,” she adds.

When the outer layer of skin dries out or is interfered with by outside forces, it can start leaking, sort of like cracks in the ceiling, says Dr. Sheldon Pinnell, professor of dermatology at Duke University Medical Center and adviser to Skinceuticals.

Alpha hydroxy acids have been shown to strengthen the epidermis so the outer layer of skin holds moisture better, Pinnell says, but the downside is that AHAs make the skin a little more sensitive to the sun.

Pinnell encourages the wintertime use of sunscreen, anyway.

“People think that because it’s not warm out, they don’t need sun protection, but the damage that the sun and ultraviolet light does to the skin is year-round. You’re not getting ‘sunburn’ but you are getting damage from UVA light. It’s what causes photo-aging changes and is part of the cause of skin cancer,” he says.

Heavy winter clothes protect your arms, legs and torso but “your face and hands get nailed,” says Pinnell, who notes that UVA rays do cut through window glass. Zinc oxide is an effective sunscreen ingredient that helps block such rays, but Pinnell personally uses formulas with topical antioxidants such as vitamins C and E.

Day also says it helps to ingest vitamins, too.