Health A-Z

Medical Content Created by the Faculty of the
Harvard Medical School

Contact Dermatitis

What Is It?

Contact dermatitis is skin inflammation. It occurs because the skin has been exposed to a substance that irritates it or causes an allergic reaction.

Many natural and artificial chemicals can trigger contact dermatitis. These include ingredients found in:

• Antibiotic ointments

• Cosmetics

• Fabric finishes

• Household cleaners

• Industrial solvents

• Laundry detergents

• Metal jewelry

• Perfumes

• Shampoos

• Soaps

Common skin exposure (contact) that can lead to contact dermatitis includes:

• Applying makeup or hair dye

• Hand washing

• Hiking near poison ivy, oak or sumac

• Housecleaning

• Shampooing hair

• Sitting near a campfire where poison ivy is being burned.

• Spraying or dabbing on perfume

• Wearing a diaper

• Wearing a metal necklace or bracelet that contains nickel

• Wearing clothes with metal snaps or zippers

• Working with industrial solvents

Doctors classify contact dermatitis into two types. The type depends on the cause of inflammation:

• Irritant contact dermatitis. This is triggered by exposure to a chemical that is poisonous (toxic) or irritating to the skin. It is not an allergic reaction.

In children, the most common form of irritant contact dermatitis is "diaper rash." This is a skin reaction in the diaper area. It is caused by prolonged contact with the natural chemicals found in urine and stool. Childhood irritant contact dermatitis also can develop around the mouth because of skin contact with dribbles of baby food or drools of saliva.

In adults, this condition is often an occupational illness. It is triggered by exposure to strong soaps, solvents or cutting agents. It is especially common among:

• Hairdressers

• Health care workers

• Homemakers

• Janitors

• Machinists

• Mechanics

But it can occur in anyone whose household chores or hobbies involve exposure to irritating chemicals.

• Allergic contact dermatitis. This is an immune reaction. It occurs only in people who are naturally oversensitive to certain chemicals.

With allergic contact dermatitis, the inflammation may not develop until 24 to 36 hours after contact with the allergen. This is because allergic contact dermatitis involves the body's immune defenses. The immune response is a process that takes some time.

Skin allergies vary from person to person. The most common types of allergens responsible are:

• A chemical found in poison ivy, oak and sumac

• Nickel and cobalt in metal jewelry, clothing snaps, zippers and metal-plated objects

• Latex in gloves and rubberized clothing

• Neomycin in antibiotic skin ointments

• Potassium dichromate, a tanning agent found in leather shoes and clothing

• Certain preservatives, such as formaldehyde