Contact dermatitis usually causes a dry, red rash, although in some cases there is discharge as in the case of a reaction to poison ivy. Occasionally, blisters form and, in more serious cases, there may be such discomfort that it interferes with normal activities. Hands are typically the most affected by such skin reactions because they touch so many different things. Any part of your body, however, that comes into contact with the offending substance is vulnerable.
Contact dermatitis can be triggered by an allergy or by an irritant. A partial list of the more common triggers includes:
plants (e.g., poison ivy, poison oak);
metallic compounds (e.g., jewelry containing nickel);
cosmetics and perfumes;
antioxidants used in textiles;
clothing (e.g. wool scarves).
If it is an allergic reaction, the first contact with the product does not cause any apparent reaction. After a few days, or even several years, however, the skin may become sensitive when it comes into contact with the substance again. Then, within a few hours, the skin becomes inflamed. A classic example is the case of a woman who wears a piece of costume jewelry with nickel next to the skin for years without any problem and then develops an allergic response. Another example is poison ivy, which as we all know causes a rash. Occasionally, the reaction may be triggered by exposure to the sun in people using certain perfumes or soaps, or taking certain medications.
If you stop having any contact with the offending substance, the dermatitis disappears in a matter of days. In the case of a first-time reaction to a powerful irritant or sensitizing agent, the eruption generally only lasts about week, decreasing progressively and usually not leaving a scar. If the eruption, however, is caused by repeated contact, it will not heal as quickly and may leave a darker area of skin that takes time to fade.
Contact dermatitis may also be produced by chemical irritants (e.g., detergents) or mechanical irritants (e.g., fibreglass particles, the rubbing of wool clothing). If the irritant is strong, a single exposure may provoke a violent reaction, but if it is weak, the reaction is progressive and develops after several days of exposure.
Making the diagnosis
Occasionally, the region affected makes it easier to find the agent involved. An eruption around the wrist is usually caused by a watch or a bracelet, eruptions under the arms are typically caused by an antiperspirant. But, in most cases, identifying the cause isn't easy. In order to make a proper diagnosis, the doctor asks about work and activities (e.g., gardening, painting, hobbies), especially about the various products in use. Detective work is sometimes needed to identify the exact cause and skin tests may used to confirm the cause.
A skin test (also called a patch test) involves applying small concentrations of the suspected substances on the forearm or back. The area is then covered with a bandage for 48 hours. If, after 3 to 5 days, the skin turns red, swells, possibly blisters and itches, then the test is positive.
The first step is to avoid coming into contact with the substances that are responsible for the eruption. Then a treatment is selected in keeping with the seriousness of the reaction. This treatment may include moisturized bandages, moisturizing preparations, lotions, creams, or cortisone ointments. In the most serious cases, a doctor may prescribe corticosteroids to be taken orally or by injection.
To promote healing:
- Avoid scratching to prevent the development of bacterial infections.
- Follow your physician's instructions.
- Avoid contact with other potential irritants.
Some people try to self-medicate with over-the-counter topical corticosteroids. This is considered ill-advised because long-term use, especially on the face, can cause thinning of the skin with visible blood vessels.