Allergic contact dermatitis

This article has been translated from Finnish to English by Semantix. You can find the original article at the web adress

Atopic eczema caused by delayed hypersensitivity and contact urticaria caused by immediate hypersensitivity are types of allergic contact dermatitis. In addition, irritant dermatitis, i.e. irritant contact dermatitis, which is a nonallergic skin reaction, is also a type of contact dermatitis.

Allergic contact dermatitis

Allergic contact dermatitis can initially cause the skin to become red, itchy, dry and flaky. It often also causes subcutaneous blisters and later peeling of the skin. The allergic contact dermatitis caused by cosmetics usually occurs on the face and especially first on the eyelids, where the skin is thin. Occupational allergic contact dermatitis occurs often as a rash in the hands. The rash always starts in the area which came into contact with the substance, but it can spread to other parts of the body as well. The rash can spread to the face either by hands or the air by the airborne particles or substances.

Allergic contact dermatitis is usually caused by low molecular weight chemicals, which easily penetrate the skin. Delayed (Type IV) hypersensitivity is mediated by sensitised T cells, i.e. memory cells. Chemicals (haptens) whose molecular weight is usually less than 1000 daltons cause allergic reaction only until they bind to a protein in the body.

The development of allergic contact dermatitis is always preceded by an asymptomatic exposure time in which the body has been in repeated contact with the allergen. The exposure time usually lasts for months or years. In some rare cases, however, a single exposure can be sufficient to develop an allergy. After the allergy has been developed, it changes permanently the way how the body responds to certain substances. In other words, allergies are permanent.

Allergic contact dermatitis, i.e. delayed hypersensitivity, is diagnosed by a series of patch tests on the skin.

Contact urticaria and protein contact dermatitis

In allergic contact urticaria, redness, swelling and raised patches that resemble nettle stings develop only in a few minutes, usually less than in half an hour, on the skin area that was exposed to the substance. The rash usually causes extreme itching. Contact urticaria reaction clears up rapidly, usually within a few hours, leaving no trace once the offending substance is no longer in contact with the skin. Symptoms are also often accompanied by other symptoms of immediate hypersensitivity, such as itchy and red eyes, sneezing, rhinitis, cough, shortness of breath and asthma.

Repeated exposure to the offending substance may result in persistent symptoms of inflammation, protein contact dermatitis. If this happens, the rash will resemble an eczema triggered by a contact with chemicals.

Allergens that cause immediate hypersensitivity are usually animal or plant proteins but, in rare occasions, they can also be chemicals. Symptoms of immediate contact urticaria can appear, for example, after using gloves made of natural rubber latex, handling flour, being licked by a dog and, in rare cases, using cosmetics that contain a certain protein (e.g. silk protein) or chemical (e.g. persulfates used to bleach hair). An immediate hypersensitivity reaction (type I) involves immunoglobulin E (IgE) mediated release of antibodies against a specific antigen and release of histamine from the mast cells.

Immediate hypersensitivity reactions are diagnosed by skin prick tests and blood tests to detect IgE antibodies specific to certain allergens (e.g. RAST test).

Kristiina Alanko, docent, dermatologist