The two main types of contact dermatitis are:
Allergic contact dermatitis: Your body has an allergic reaction to a substance (allergen) that it doesn’t like. Common allergens include jewelry metals (like nickel), cosmetic products, fragrances and preservatives. It can take several days after exposure for an itchy, red rash to develop.
Irritant contact dermatitis: This painful rash tends to come on quickly in response to an irritating substance. Common irritants include detergents, soap, cleaners and acid.
Often, you will need allergy skin tests called patch tests. Patch tests are a safe, easy way to detect contact allergies. Patch tests differ from intradermal (injection), prick, or scratch skin tests, which put the allergen into the skin. In patch tests, the dermatologist puts small amounts of your suspected allergens on strips of tape and applies these strips on the skin. After two days, the doctor removes the strips. A red spot at the site of the patch shows an allergy.
Mild rashes most often respond to steroid creams and/or oral (taken by mouth) antihistamines. For very aggravated rashes, your dermatologist may give you oral corticosteroids or injections (shots). You may need other anti-inflammatory medicines or immunologic therapies. If your skin becomes infected, you may get antibiotics.
People who get allergic contact rashes should avoid the allergen that causes the reaction. Your dermatologist will help you find out the items you need to avoid. Also, the dermatologist can suggest products that do not contain the allergen and will not cause reactions.
Allergic contact dermatitis is a Type IV hypersensitivity reaction, caused by a different immunologic mechanism than hives, angioedema, or anaphylaxis. However, very rarely, patients may have immunologic dysfunction which results in multiple types of concurrent hypersensitivity reactions. Thus, it is possible that people with contact dermatitis can develop hives (urticaria) and swelling (angioedema) after coming into contact with an allergen. Hives are red, raised, itchy skin welts. Angioedema is swelling deep under the skin.