AAIQ   The Association of Allergists and Immunologists of Québec

Contact dermatitis

What is contact dermatitis?

Contact dermatitis is an affliction of the skin caused by contact with a foreign substance. There are two types of contact dermatitis: an irritative dermatitis and an allergic contact dermatitis. An irritative contact dermatitis, the most common, is caused by diverse substances which irritate the skin and provoke inflammation. In allergic contact dermatitis specific immune cells are involves and become sensitized to a particular substance. In this way, the same cells will become active each time the skin comes into contact with the substance causing the initial reaction.

What are the symptoms of a contact dermatitis?

A skin eruption in the region of the skin exposed to the responsible agent will occur from hours to days after the exposure. The skin lesions are generally red and accompanied by itching.

Contact dermatitis

In irritative contact dermatitis the skin can appear dry with fissuring, whereas in an allergic contact dermatitis, small vesicles (blisters) can appear. In either case, contact dermatitis can be confused with several other skin diseases, such as atopic dermatitis (often simply called "eczema").

What are the causes of a contact dermatitis?

A tremendous variety of chemical products (often encountered in the workplace, for example) such as detergents, solvents and creams are responsible for irritative dermatitis. In babies, the common diaper rash is a form of irritative contact dermatitis. Allergic contact dermatitis is often caused by: nickel, present in numerous forms of jewelry; fragrances and perfumes found in many cosmetics, shampoos, soaps and creams; certain plants such as poison ivy; many medications.

How does one diagnose a contact dermatitis?

Means of prevention

The history and examination of the skin will often suggest the diagnosis. When the history is unable to identify the cause of the reaction, one can proceed with patch testing. These are not conventional allergy tests, and are only performed by certain allergists and dermatologists. These tests may involve 3 closely spaced visits to the physician. On the first visit, adhesive tape containing "patches" of particular substances are applied to the back (or the arms) and the reaction is noted over successive visits.

How is a contact dermatitis treated?

The key to treatment is the identification and avoidance of the substance causing the skin reaction. Cold compresses can help to reduce itching. The eruption can often be treated locally with cortisone-based creams. But when the reaction is important or severe, the physician may recommend a short treatment of oral cortisone.

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Nha Uyen Nguyen-Luu, MD FRCPC
(translation: Andrew Moore, MD FRCPC)