Allergic Contact Dermatitis or Skin Rash

Woman by tree scratching arm

Allergic contact dermatitis accounts for 20% of all contact dermatitis reactions. Allergic contact dermatitis is a delayed hypersensitivity reaction that involves the interaction of allergens and antibodies, which occurs in phases.

Allergic Contact Dermatitis Sensitization Phase
During this phase, an antigen comes in contact with the skin. Because most of the antigens that cause this type of reaction have a low molecular weight, they can easily penetrate the outer layer of the properly functioning epidermis.

The antigen is processed by cells in the basal layer of the epidermis and then presented to white blood cells called T lymphocytes. These T lymphocytes recognize the antigen as foreign and circulate through the bloodstream back to the epidermis

Allergic Contact Dermatitis Elicitation Phase
The elicitation phase occurs in sensitized people who are reexposed to the antigen. The T lymphocytes in the epidermis recognize the antigen as foreign and produce inflammatory chemicals designed to eradicate the antigen. Unfortunately, these chemicals produce a characteristic rash in the skin. The allergic contact dermatitis rash develops within 12 to 48 hours of reexposure to the antigen and lasts for 3 to 4 weeks.

Allergic Contact Dermatitis Appearance
The shape and location of the rash are important clues to the cause of the allergen if the pattern of the rash corresponds exactly to the shape of the offending agent such as a watch, metal belt buckle, or waistband.

Unfortunately, in most cases, the rash does not correspond exactly to the areas contacting the allergen. A list of common allergens by rash distribution can be found here. The allergic contact dermatitis rash is usually very itchy and consists of redness, scaling, fissuring, vesicles, and lichenification.

  • Close-up picture of allergic contact dermatitis
  • Picture of allergic contact dermatitis on the arm
  • Picture of allergic contact dermatitis with distinct borders
  • Picture of allergic contact dermatitis on the cheek

Allergic Contact Dermatitis Treatment
The mainstay of treatment for allergic contact dermatitis is avoiding the offending allergen if it can be determined. Other helpful measure to consider, especially if the allergen cannot be identified include:

  • Minimize products for topical use
  • Use ointments instead of creams
  • Avoid botanical extracts found in "fragrance-free" or "natural" products as these can be very allergenic
  • Topical steroids - Medium- to high-strength topical steroids may be needed to reduce inflammation and itching