Text A. Types of Dermatitis.

 

Part I. Contact Dermatitis

Contact dermatitis is inflammation caused by con­tact with a particular substance; the rash is confined to a specific area and often has clearly defined boundaries.

Substances can cause skin inflammation by one of two mechanisms - irritation (irritant contact dermatitis) or allergic reaction (allergic contact dermatitis). Even very mild soaps, detergents, and certain metals may irritate the skin after fre­quent contact. Sometimes repeated exposure, even to water, may dry out and irritate the skin. Strong irritants, such as acids, alkalis (such as drain cleaners), and some organic solvents (such as acetone in nail polish remover), may cause skin changes in a few minutes.

With an allergic reaction, the first exposure to a particular substance (or in some cases, the first several exposures) doesn't cause a reaction, but the next exposure may cause itching and dermatitis within 4 to 24 hours. People may use (or be exposed to) substances for years without a prob­lem, then suddenly develop an allergic reaction. Even ointments, creams, and lotions used to treat dermatitis can cause such a reaction. About 10 percent of women are allergic to nickel, the most common cause of dermatitis from jewelry. People may also develop dermatitis from any of the ma­terials they touch while at work (occupational dermatitis).

When dermatitis results after a person touches certain substances and then exposes the skin to sunlight, the condition is called photoallergic or phototoxic contact dermatitis. Such substances include sunscreens, aftershave lotions, certain perfumes, antibiotics, coal tar, and oils.

 

Common Causes of Allergic Contact Dermatitis

Cosmetics:hair-removing chemicals, nail polish, nail polish remover, deodorants, moisturizers, aftershave lotions, perfumes, sunscreens

Metal compound (in jewelry):nickel

Plants:poison ivy, poison oak, poison sumac, ragweed, primrose

Drugs in skin creams:antibiotics (penicillin, sulfonamides, neomycin), antihistamines (diphenhydramine, promethazine), anesthetics (benzocaine), antiseptics (thimerosal), stabilizers

Chemicals used in clothing manufacturing:tanning agents in shoes; rubber accelerators and antioxidants in gloves, shoes, undergarments, other apparel

 

Symptoms

The effects of contact dermatitis range from a mild, short-lived redness to severe swelling and blisters. Often, the rash contains tiny, itching blis­ters (vesicles). At first, the rash is limited to the contact site, but later it may spread. The rash area may be very small (for example, the earlobes if earrings cause dermatitis), or it may cover a large area of the body (for example, if a body lotion causes dermatitis).

If the substance causing the rash is removed, the redness usually disappears in a few days. Blis­ters may ooze and form crusts, but they soon dry. Residual scaling, itching, and temporary thick­ening of the skin may last for days or weeks.

Diagnosis

Determining the cause of contact dermatitis isn't always easy because the possibilities are endless. Also, most people aren't aware of all the substances that touch their skin. Often, the loca­tion of the initial rash is an important clue.

If a doctor suspects contact dermatitis but a careful process of elimination doesn't pinpoint the cause, patch testing can be performed. For this test, small patches containing substances that commonly cause dermatitis are placed on the skin for 2 days to see if a rash develops beneath one of them.

Although useful, patch testing is complicated. A doctor must decide which substances to test, how much of each substance to apply, and when the tests should be done. Also, the results of patch testing can be hard to interpret. Tests may be falsely positive or negative. Most people can discover the source of their dermatitis without patch testing by systematically eliminating pos­sible causes. However, patch testing can provide important clues in identifying the cause.

Treatment

Treatment consists of removing or avoiding whatever is causing the contact dermatitis. To prevent infection and avoid irritation, a person should clean the area regularly with water and gentle soap. Blisters should not be cut open. Dry bandages may also help prevent infection.

Corticosteroid creams or ointments usually relieve the symptoms of mild contact dermatitis, unless the person has a lot of blistering, as is common with poison ivy. Corticosteroid tablets (such as prednisone) are sometimes prescribed for severe cases of contact dermatitis. Although antihistamines relieve itching in some situations, they are not particularly helpful in most cases of contact dermatitis.