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What is allergic contact dermatitis?

Irritant Contact Dermatitis is Non-immunologic condition that is caused by an external agent that directly damages the skin. It is the most common skin reaction.

Allergic Contact Dermatitis

Allergic contact dermatitis accounts for 20% of all contact dermatitis reactions. Allergic contact dermatitis is a delayed hypersensitivity reaction that involves 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 re-exposed 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 re-exposure 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.

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

Source: About Health

Common allergens that can make dermatitis worse

Common Allergens by Location of Rash

Allergic contact dermatitis is a delayed hypersensitivity reaction that involves interaction of allergens and antibodies. The location of the rash can give important clues to the type of allergen causing the rash. The following lists give common allergens that cause allergic contact dermatitis grouped by location of the rash.

Dermatitis on Scalp and Ears

Shampoos
Hair dyes
Topical medications
Metal earrings
Eyeglasses
Rubber ear plugs

Face

Cosmetics - preservatives, emulsifiers, fragrances

Acne medications - Benzoyl peroxide, Retin-A
Aftershave lotions
Respirators, masks, aerosolized mists (machinists), volatile organic substances
Chemicals applied to the scalp can spread to the face, ears, and neck - the scalp may not be involved because it is more resistant
Airborne allergens such as poison ivy from burning leaves or ragweed
Sunscreen ingredients such as oxybenzone and benzophenone No. 3

Dermatitis on Eyelids

Nail polish
Cosmetics
Contact lens solution
Metal eyelash curlers
Rubber makeup sponges
Goggles
Neck

Necklaces especially made of metals or exotic woods
Airborne allergens such as ragweed
Perfumes
Aftershave lotions
Cosmetics
Textiles dyes or formaldehyde resins in clothing
Trunk

Textiles especially if the rash does not involve the armpits or areas covered by undergarments
Azo-aniline dyes found in colored clothing
Urea formaldehyde resins found in wrinkle-resistant clothing
Rubber allergens in elasticized waist bands or spandex bras
Fragrances
Preservatives in moisturizing lotions
Topical medications
Sunscreens
Poison ivy
Plants
Metal belt buckles
Arms

Same as hands
Watch and watchband
Soap
Moisturizers
Fingertips

Glue
Disinfectants
Armpits

Deodorants
Clothing
Hands

Soaps and detergents
Foods
Spices
Poison ivy
Industrial solvents and oils
Cement
Metal
Topical medications
Rubber gloves
Genitals

Poison ivy - transferred by hand
Rubber condom
Diaphragms
Pessaries
Anal Region

Hemorrhoid preparations containing benzocaine or nupercaine

Lower Legs

Topical medications
Moisturizers containing fragrances or preservatives

Source: About Health

The form of dermatitis that results from a delayed allergic reaction to contact with an allergen. Characterized by inflammatory papules and vesicles. Can be caused by fragrances, small molecule preservatives, etc.