Allergic contact dermatitis is an extremely itchy rash that develops when someone comes into contact with a substance to which he or she is allergic.

These substances (“allergens”) are harmless to most people but trigger immune reactions in those who are sensitive. Only a small amount of the allergen is required to trigger an allergic reaction.

Repeated exposure of the skin to an allergen is required to develop contact dermatitis. Most people might be exposed to an allergen for years before finally developing a rash. However, once a person’s skin becomes sensitized to a particular substance, that person usually remains sensitive to it for life.

Allergens that commonly trigger allergic contact dermatitis include:

  • Plants (poison oak, poison ivy)
  • Metals, particularly nickel allergy. Nickel is found in jewelry (earrings, watches, necklaces), buttons (inside portion of jeans), or belt buckles
  • Fragrances (including those found in lotions, shampoos, and other cosmetics)
  • Preservatives (found in lotions, or leather and other fabrics)
  • Rubber (gloves)
  • Hair dyes
  • Glues
  • Medications (Neosporin)

After exposure to an allergen, the skin may appear red, swollen, and blistered, or dry and bumpy. The location of the rash helps to determine the source of the allergy since it develops where the allergen contacts the skin.

For instance, a rash on the neck or wrist may suggest an allergy to the metal (nickel) found in a necklace or wristwatch. Rashes on both feet may be due to chemicals found in the leather or rubber of shoes.In severe cases, the rash may extend beyond the point of contact and appear elsewhere in the body.

The rash of contact dermatitis may start as soon as several hours after contact with the allergen. And it can take days to weeks to heal even after the allergen is removed from the skin.

If the cause of the allergic reaction is uncertain, your doctor may perform a patch test. This an an allergy test for the diagnosis of allergic contact dermatitis. The suspected allergen may be applied several times a day to a small patch of sensitive skin (such as the inner arm) for several days. The area is then monitored for changes.

The focus of treatment for allergic contact dermatitis is avoidance of the allergen (the substance that causes the allergy).

The symptoms of allergic contact dermatitis might be treated with one or more of the following:

  • Anthistamines to control the itching
  • Moisturizers, to heal damaged skin and provide a barrier
  • Topical corticosteroids
  • Oral steroids, such as prednisone, used for a short period for severe cases
  • Topical immunomodulators (Elidel®, Protopic®)