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Dry, itchy skin is a common companion when the humidity drops, especially as we get older. “The oil-producing glands that lubricate skin shrink and don’t work as efficiently,” says Amy Kassouf, a dermatologist at the Cleveland Clinic.

But when is it just dry skin, and when is it something that needs treatment? Here’s what you need to know about three skin conditions that can flare up in the winter:

Eczema

More than 30 million Americans have the patches of red, thick, scaly, itchy skin of eczema. Older adults are at higher risk for asteatotic eczema, which often causes intense dryness and itchiness on the lower legs. Eczema crops up commonly in people with asthma or hay fever, but stress, dry heat, allergens and fragrances and dyes in household products can set it off, too, says Jonathan Silverberg, director of Northwestern Medicine’s Multidisciplinary Eczema Center in Chicago.

DIY care: Moisturize several times per day, and run a humidifier when your heat is on at home. Use dye- and scent-free detergents and soaps, and wash new clothes and bedding before use. Occasional use of over-the-counter hydrocortisone cream helps calm the itch.

See a doctor if you see little change after several weeks of self-care or if you have severe itching or patches that blister or ooze. The doctor may prescribe a steroid cream or, in severe cases, an oral immunosuppressant for the itch. Phototherapy, which uses ultraviolet light to tame inflammation, is an option, too.

Psoriasis

An estimated 6.7 million Americans have this chronic condition, marked by flaky, itchy, slightly elevated patches covered with silvery skin cells. These plaques develop when skin cells grow too rapidly, flaring up when “something triggers the immune system to become overactive,” says Ronald Prussick, medical board member at the National Psoriasis Foundation. Triggers can include stress, skin injury or infection, allergies and certain medications. And “scratching an itchy spot can create new psoriasis in that area,” says dermatologist Jessica Krant, a member of the Consumer Reports medical advisory board.

DIY care: To ease itching and loosen dead skin, soak for 15 minutes in a lukewarm bath to which you’ve added baby oil, oilated oatmeal or Epsom salts. A shampoo or an over-the-counter cream with salicylic acid can soften plaques; one with coal tar can reduce discomfort. You can also subdue itching with hydrocortisone cream.

If self-care doesn’t help, see a doctor, who might prescribe a biologic drug for inflammation, methotrexate to slow skin-cell growth, or phototherapy.

Rosacea

A chronic condition that’s more common after age 30, rosacea can lead to redness, bumps and pustules, usually on the face. Some people experience dryness, stinging, itching and burning. “The skin of rosacea patients is very sensitive,” says John Wolf, chair of dermatology at Houston’s Baylor College of Medicine. Triggers include cold or hot weather, indoor heat, stress, sun, wind, alcohol, hot baths, vigorous exercise and spicy food.

DIY care: Use a gentle facial cleanser and a gentle moisturizer before bed, and wear a broad-spectrum sunscreen for sensitive skin with an SPF of at least 30.

See a doctor if your symptoms don’t resolve or if they cause discomfort or emotional distress. Prescription treatments might include a topical ­anti-inflammatory cream or an oral antibiotic for more-severe inflammation and redness. Laser or light therapy can also be used to reduce redness.

Cold-weather skin soothers

Whether it’s simple dry skin or a specific skin condition, try these tips:

●Turn down the thermostat a few degrees. “It may keep the air from drying out as much, and cooler air is less likely to aggravate your itch,” Northwestern’s Silverberg says.

●Bathe briefly and use tepid water. The hotter the water, the more skin oils you strip away.

●Moisturize after bathing, while you’re slightly damp. Use a product that’s fragrance-free, hypoallergenic or made for sensitive skin.

●Run a cool-mist humidifier. Or place pans of water near heating vents to moisten indoor air. Humidity should be 30 to 60 percent (40 to 50 percent if you have allergies or asthma).

●Stick to fragrance-free soaps. Also, use detergents made for sensitive skin.

Copyright 2016. Consumers Union of United States Inc.

For further guidance, go to www.ConsumerReports.org/Health, where more detailed information, including CR’s ratings of prescription drugs, treatments, hospitals and healthy-living products, is available to subscribers.