What Is It?

Contact dermatitis is a form of skin inflammation that occurs because the skin has been exposed to a substance that irritates it or that causes an allergic reaction. A long list of natural and synthetic chemicals can trigger contact dermatitis, including those found in soaps, household cleaners, laundry detergents, metal jewelry, perfumes, industrial solvents, cosmetics, fabric finishes, shampoos and even antibiotic ointments. As a result, the problem can develop in an almost endless variety of ways. Common types of skin exposures (or "contacts") that can lead to contact dermatitis include hand washing; housecleaning; wearing a diaper; hiking near poison ivy, oak or sumac; spraying or dabbing on perfume; wearing a metal necklace or bracelet that contains nickel; wearing clothes with metal snaps or zippers; shampooing hair; applying makeup or hair dye; working with industrial solvents; and sitting near a campfire where poison ivy is being burned.

Doctors classify contact dermatitis into two types, depending on the cause of the skin inflammation:

• Irritant contact dermatitis (ICD) - ICD is triggered by exposure to a chemical that is naturally toxic (poisonous) or irritating to human skin. It is not an allergic reaction. In children, the most common form of ICD is diaper dermatitis, a skin reaction in the diaper area that is caused by prolonged contact with the natural chemicals found in urine and stool. Childhood ICD also can develop around the mouth because of skin contact with dribbles of baby food or drools of saliva. In adults, ICD is often an occupational illness that can be triggered by exposure to strong soaps, solvents or cutting agents. It is especially common among health care workers, homemakers, janitors, mechanics, machinists and hairdressers, but it can occur in anyone whose household chores or hobbies involve exposure to irritating chemicals.

• Allergic contact dermatitis (ACD) - This form of contact dermatitis is an immune reaction that occurs only in people who are naturally oversensitive to certain chemicals. With ACD, the inflammation may not develop until 24 to 36 hours after skin contact with the substance (allergen). This is because ACD involves the body's immune defenses, a process that takes some time. Specific skin allergies vary from person to person. However, among the most common types of allergens responsible for ACD are a chemical found in poison ivy, oak and sumac; nickel and cobalt in metal jewelry, clothing snaps, zippers and metal-plated objects; neomycin in antibiotic skin ointments; potassium dichromate, a tanning agent found in leather shoes and clothing; latex in gloves and rubberized clothing; and certain preservatives, such as formaldehyde. An estimated 20% of people in the United States is probably at risk of ACD because of skin sensitivity to at least one common chemical allergen