SKIN needs extra care if it is to survive the onslaught of winter. The big news recently is alpha hydroxy acid (AHA) treatment, which works to give long-term effects in minimising fine lines. It is encouraging that not only the beauty houses and those responsible for developing these treatments support this view. While beauty systems are often little more than an improvement or a variation on existing products, the AHAs are new to the cosmetics world. Australian dermatologist Dr Peter Cowen says these agents have been shown to increase in the skin the amount of collagen and the amount of elastin production. He said at the Asia Pacific Cosmetics and Skincare seminar that AHAs enhanced the production of glycoaminoglycens. The seminar was organised recently by the Hong Kong Trade Fair Group. ''These are key factors in binding water to the skin and making the skin look more youthful,'' he said. Alpha hydroxy fruit acids are so called because they are derived from malic acid in apples, citric acid, glycolic acid and lactic acid from sour milk. The results speak for themselves: there has been a rush as leading cosmetics houses scramble to get their version on the market. Among the first was Estee Lauder with Fruition Triple Reactivating Complex. The treatment provides immediate comfort for dry skin and, over the longer term, reduces lines and wrinkles while improving elasticity and colour. It is most beneficial to skin that is dull, rough, flaky or showing signs of fine lines. It can also be used for oily or dry skin. Yves Saint Laurent's answer to dehydrated skin is Hydra Fluide, which has a sun protection factor of 15. These SPFs are vital as women learn more about the damaging effects of the sun, even in winter. Dr Cowen said the SPF found in cosmetic products was just as effective as that in sun screens. However, because these were being incorporated into products made especially for faces, they were less harsh than normal sun creams. Hydra Fluide is an ally to a combination of oily skins. Oily skin also suffers from surface dehydration. But Fluide is a light lotion and has no oils in it, so it is absorbed immediately into the skin. It helps to form ''intercellular cement'', which progressively rises to the surface of skin, assuring the cohesion of skin cells. It also carries lipids to the corneal layer, which results in healthier skin that can retain its suppleness. Clarins, meanwhile, is pushing the beauty frontier even further back with Le Maquillage, which it claims is the first make-up range with anti-pollution action. Clarins said it had the test results to support its claims. Skin discomfort is a warning signal that the ageing process is accelerating. Just as it is necessary to protect skin against the sun, it has become necessary to protect skin against the environment. Air pollution has a corrosive, oxidising effect that contributes to the skin becoming sensitive and lines appearing prematurely.