Cold temps outdoors, dry heat blasting indoors, and too little sunlight all can aggravate skin conditions. But what exactly is the problem when your skin or scalp feels itchy or scaly? Is that dusting on your favorite sweater dandruff or something more serious? Use our handy sympt-o-meter to help you find out.

Key symptom: Red, itchy patches
Best fix: Ointment, antihistamines

Eczema, marked by swollen, red skin, tends to itch a lot—and it shows up twice as often in women. (Thirty million Americans have it.) The patches, which have many triggers including winters dry air, can pop up anywhere but usually appear on your arms or behind your knees.

Eczema may also flare near your neck hairline and earlobe creases. Its often seen in people with asthma, allergies, or pet sensitivities, says Kelly Cordoro, MD, an assistant professor of dermatology at the University of California, San Francisco. Antihistamines and steroid ointments can ease the itch.

Next Page: Dandruff [ pagebreak ]

Key symptom: Flakes in your hair
Best fix: Medicated shampoo

If you see moist, yellow scales in your hair or in extra-oily areas (say, near your forehead or eyebrows), or if those telltale flakes appear on your shoulders, it may be dandruff, Dr. Cordoro says. The problem, in part, is a shedding of dead skin cells at a rate thats faster than normal.

Overly dry or oily skin, an overgrowth of a yeastlike fungus common to everyone, and even stress may lead to dandruff. The good news for dandruff sufferers with oily skin: Winter usually gives you a break. The best treatment is a daily dose of an antidandruff shampoo that contains pyrithione zinc and selenium sulfide.

Key symptom: Thick, silvery flakes
Best fix: Steroid ointment, meds

If you have thick, scaly, silvery spots on your body and/or scalp that are tender or itchy, you could have psoriasis, Dr. Cordoro says. This skin disease is caused by a misfiring immune system and may also be connected to arthritic joint pain.

Up to 7.5 million Americans suffer from psoriasis, and the diminishing sunlight and dry air in winter might make it worse or cause an outbreak. Most people can benefit from a topical steroid ointment, Dr. Cordoro says. Light therapy can also help. And for serious cases, some docs recommend oral or injected meds, such as Enbrel.