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Differences of Allergic and Irritant Contact Dermatitis

Dermatitis is a medical condition in which areas of the skin becomes irritated and inflamed. Contact dermatitis is a specific form of skin inflammation that occurs from direct contact with causative agents. There are two types of contact dermatitis: irritant dermatitis and allergic contact dermatitis.

Irritant dermatitis:

Irritant dermatitis is five times more common than allergic contact dermatitis. The skin inflammation of irritant dermatitis results from physical and chemical alteration of the epidermal layer, which is the most superficial layer of the skin.

Agents that commonly cause irritant dermatitis are organic solvents such as alcohol, turpentine and acetone, latex, and surfactants (ex. sodium lauryl sulfate in cosmetics) or detergents at high concentrations. This form of dermatitis is immediate in onset but may take days to weeks to resolve. The rash of irritant dermatitis has an indistinct border on the skin and is often associated with a burning or itching sensation.

Allergic contact dermatitis:

Allergic contact dermatitis may be less common than irritant dermatitis, but it occurs significantly more frequently in individuals who have a genetic predisposition toward allergic conditions. Infants and elderly tend to suffer from allergic dermatitis less commonly than other age groups because they have a decreased cell-mediated immune response which is required for the allergic reaction to occur.

Allergic dermatitis is considered a Type II delayed hypersensitivity reaction. This reaction occurs in response to specific allergens that are low molecular weight haptens. Haptens are small molecules that elicit an immune response only when they are attached to other proteins. For example the poison ivy hapten is called quinine. This molecule attaches to skin proteins and activates the immune response that results in the raised, itchy red rash.

There are three phases of this Type II hypersensitivity reaction: sensitization (first exposure to the hapten), elicitation (subsequent exposure that elicits an immune response) and finally resolution. The rash that occurs from allergic contact dermatitis develops approximately 24 to 48 hours after exposure to the allergen. In contrast to irritant dermatitis, the border of the allergic dermatitis rash corresponds to the area of contact.

Common examples of allergic dermatitis include reactions to Rhus toxicodendron plants (poison ivy and poison oak), reaction to the medication Neomycin, and reactions to specific fragrances and preservatives.

Irritant dermatitis and allergic dermatitis are two types of contact-induced skin reactions. These two forms of dermatitis cause similar symptoms but can often be distinguished by the time that lapses between contact with the inciting agent and eruption of the skin rash. Individuals with a severe or persistent skin rash should contact their health care provider.