Q. My 4-month-old son has had a red, bumpy rash on his face, especially his cheeks. It seems to be spreading, because he's starting to get it on some other parts of his body. Our doctor says he has eczema and that he may have it for years before outgrowing it. In the meantime, what should we be doing about it?

A. Eczema, also known as atopic dermatitis, is an allergy-related skin rash that affects 10 percent of infants and 3 percent of the overall population, according to the American Academy of Dermatology. In children, it usually develops within the first five years of life.

Eczema causes intense itching. The red rash develops when the itchy areas are scratched. A vicious cycle develops: More scratching leads to more redness, which is more itchy than before. As it worsens, the rash can also develop tiny bumps and oozing. Over time, the skin can become crusted, scaly and thickened. As it heals, the affected area may develop light or dark spots.

In infants, the rash commonly affects the face, neck, chest, arms and legs. In children, eczema typically affects the creases in front of the elbows, behind the knees, behind the ears and under the neck. In later life, hand eczema is common.

The cause of eczema isn't known, but it seems to stem from a combination of heredity and environmental factors. Eczema runs in families. If one parent has it, a child has about a 1-in-4 chance of developing it. It also tends to occur in families that have other atopic, or allergic, conditions, such as asthma and hay fever (allergic rhinitis). In fact, many people with eczema also have allergic rhinitis, asthma or both.

Many factors can trigger flare-ups of eczema. The most important of these are scratching, dryness of the skin and skin irritants. Common irritants include soaps, detergents, cleaners, greases, perfumes and wool. Some doctors feel that emotional stress may worsen eczema, although it's also likely that the eczema itself causes stress.

Allergens don't seem to play a major role in causing eczema, but the condition can be aggravated by allergens such as fungi, dust mites, pollen, animal dander and foods. Testing and treating for allergies isn't typically helpful, but it might be considered in severe cases.

A doctor will diagnose eczema by the way it looks, how it changes over time, how it responds to treatment and through other clues from a medical history, such as a family history of eczema and other atopic disorders. Other skin conditions that can look like eczema include contact dermatitis, seborrhea and heat rash. To prevent eczema from getting worse, keeping the skin moist is key. Avoid frequent washing with soaps, which will dry the skin. After bathing, coat the skin with lubricants to seal in the moisture. If possible, keep the humidity from getting too low in the house. Avoid wool, especially if it seems to worsen the rash. Cotton clothing is often recommended.

For flare-ups of the rash, with weeping or oozing, dressings soaked in Burow's solution, available over the counter, can help. Apply them several times a day for about 20 minutes. Oatmeal baths can also help.

Ointments can be used to trap moisture in the skin. Plain petroleum jelly works well. You can also use other moisturizing creams. If an ointment or cream seems to make the rash worse, stop using it. Your child may be reacting to a fragrance or irritating chemical in it.

Your doctor may prescribe strong steroid creams to initially control the rash. Be careful about using these for more than a couple of weeks at a time. Avoid covering large areas or the face, because this can increase the risk of complications.

If the itching is severe, antihistamine pills or liquid can lessen the itch. They will also make your child slightly drowsy and less likely to scratch. Once the rash is under control, you can use over-the-counter cortisone cream to treat the rash at the first sign of a flare-up.

For more information about eczema, contact the National Eczema Association, 1220 S.W. Morrison St., Suite 433, Portland, OR 97205. The association can be reached by telephone at 1-800-818-7546 and on the Web at www.eczema-assn.org.

Jay Siwek, chairman of the department of family medicine at Georgetown University Medical Center, practices at the Fort Lincoln Family Medicine Center and Providence Hospital in Northeast Washington.

Consultation is a health education column and is not a substitute for medical advice from your physician. Send questions to Consultation, Health Section, The Washington Post, 1150 15th St. NW, Washington, DC 20071. Questions cannot be answered personally.