If you’re silky smooth from head to toe, you can thank science for that. Both hair and skin are made of proteins and lipids (good fats), which help retain moisture. Of course, you need regular cleansing to remove the extra oil that leaves you greasy.But as the bitter winter air creeps in, even the most hair-blessed of us get flyaways and static. Being weathered with age (and, weather!) sheds lipids in the hair, leaving you with rougher, lifeless locks. How to achieve the delicate balance? We asked Amy McMichael, M.D., chair of the Department of Dermatology at Wake Forest Baptist Medical Center in Winston-Salem, N.C., how to treat your hair this winter.QUIZ: How Old Does Your Hair Look?YB: Hair gets so dry in the winter. What gives?AM: Heat styling, chemical straighteners and coloring agents all can strip the lipids and allow damage to the hair shaft. This is why it is important to use moisturizing shampoos and conditioners (try Pantene Daily Moisture Renewal) that are geared towards your hair type. For those with thin hair, too-heavy moisturizers will leave the hair limp and too greasy, while too-light moisturizing products will not help enough for thick damaged hair.YB: So how can we moisturize our hair without looking like a greaseball?AM: Shampoo and conditioning products geared to hair type (thin, thick, color or chemical treated) will help. But often, this will not be enough to coat the hair for the all the days between washing. To help maintain a more moisturized hair shaft, daily leave-on products can be very helpful in the maintenance of smooth hair shafts, minimizing frizz, as well as minimizing the heavy weighed-down feeling that a wash-off conditioning product will cause if left on the hair.Among other agents, products with dimethicone-coating agents work nicely to smooth the hair without leaving it greasy. However, a high concentration of dimethicone in products can cause a very oily hair shaft. (If it’s high on the ingredient list, it’s safe to assume there’s more of it!)MORE: Ingredients for Younger HairYB: Do hair and skin get oily at about the same rate?AM: Hair and skin oiliness rates may be similar, but they must be cleansed in a different way. Those who have oily skin on the scalp usually have oily skin on the face. But we would never recommend cleansing the face just once weekly. Also, facial skin is much more sensitive than the scalp, so daily cleansing of the face must be accomplished with mild cleansers.YB: So, how often you should wash your hair?AM: There is no right frequency for hair washing. If your hair has a tendency to be oily, washing may need to be as frequent as daily. But this may change in the winter when humidity is low and hair washing can be more like every other day or less frequently.What is important is to cleanse the scalp at least weekly in most cases. This will allow the scalp and hair to be cleansed of the dirt and sebum that attaches itself to the hair follicles through the week. For some women with very kinky or curly hair, hair washing frequency may be as low as every other week.