Excerpt from Dermatitis, Contact

Synonyms, Key Words, and Related Terms: contact allergy, contact sensitivity, dermatitis venenata

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Background: Contact dermatitis is probably the most commonly encountered immunologic disease by dermatologists. In 1895, Jadassohn described contact allergy to mercury and is regarded as the father of contact dermatitis. Prior to this described observation, few physicians recognized the concept of contact hypersensitivity.

The field began to grow in the 1920s with further studies describing the phenomenon and has culminated in the modern era, present day, when volumes of information on the topic are available. Entire books are available listing compounds that have been noted to cause the disease process. An example is Fisher's Contact Dermatitis, a 1,117 page text that breaks down the subject by occupation, plants, and every other conceivable classification.

Pathophysiology: Contact dermatitis is due to either allergic reaction or, more commonly, irritant exposure. Irritants usually are acids, alkalis, resins, or other chemicals, and frequently are found in drugs, dyes, plants, preservatives, cosmetics, and metals. Excessive moisture also may act as an irritant.

Irritants (as small molecular weight haptens) form a complete antigen by binding to dermal proteins and causing a sensitization (of T lymphocytes) on first contact and an inflammatory response on subsequent exposure. Allergic contact dermatitis occurs in sensitized individuals through the mechanism of type IV, cell-mediated immunity. Reexposure to sensitized antigens causes delayed hypersensitivity.

Frequency:

In the US: Incidence is extremely common; estimates vary.

Race: No racial predisposition seems to exist.

Sex: Men and women appear to be affected equally.

Age: With regard to irritant contact dermatitis, all age groups appear to be affected in similar proportions. Allergic contact dermatitis generally does not occur in children younger than 5 years or in elderly individuals because their immune systems do not respond to antigens in this manner.