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Contact dermatitis

Dermatitis is an inflammation of the skin. Contact dermatitis is a localised rash or irritation of the skin caused by contact with a substance.

Substances that cause contact dermatitis in many people include "poisonous" plants such as hellebores, chrysanthemums, primroses and primulas, certain foods, some metals, cleaning solutions, detergents, cosmetics, perfumes, industrial chemicals, and latex rubber.

Contact dermatitis causes

There are two types of contact dermatitis: allergic and irritant.

Like all allergic reactions, allergic contact dermatitis results from a reaction of the immune system.

  • The immune system overreacts to the substance, usually an animal or vegetable protein. The immune system is activated to produce antibodies against this allergen. This overreaction is often called a hypersensitivity reaction.
  • The antibody, called immunoglobulin E or IgE, is stored on special cells called mast cells.
  • When they come into contact with the allergen, the antibodies promote the release of chemicals and hormones called mediators. Histamine is an example of a mediator.
  • It is the effects of the mediators that cause the symptoms of the allergic reaction, in this case an itchy rash and swelling.

In allergic contact dermatitis there is a skin reaction to something that has touched your skin at that site. Unlike most allergic reactions, the trigger is external rather than internal.

  • Your initial exposure does not cause a rash. However, it sensitises your skin so that you will react to the next exposure. If you seem to react the first time you are exposed to an agent, you were probably exposed before without knowing.
  • Common plant allergens that cause dermatitis include hellebores, chrysanthemums, primroses and primulas.
  • Many other substances can cause allergic reactions, including hair dyes or straighteners; the metal nickel which is found in jewellery, belt buckles and watch straps - tanning agents in leather; latex rubber; and citrus fruit, especially the peel.
  • The fragrances in some soaps, shampoos, lotions, perfumes, and cosmetics can cause a reaction.
  • Even certain medications applied to the skin can cause dermatitis.

Irritant contact dermatitis results from coming into contact with a substance that directly damages your skin.

  • The longer the substance remains on the skin, the more severe the reaction.
  • Many chemicals, including industrial cleaning products and solvents, can cause this condition.
  • Household cleaners such as detergents can also cause dermatitis.

People with other skin conditions, such as eczema, are more likely to develop contact dermatitis.

Contact dermatitis symptoms

  • A red rash is the usual reaction. It often appears immediately in irritant contact dermatitis, but sometimes in allergic contact dermatitis the rash does not appear for one to two days after the exposure.
  • Your skin may swell or blister, or you may get a raised red rash, called hives, or sometimes the rash appears in a pattern that points to the offending agent.
  • Your skin will itch and perhaps burn. Irritant contact dermatitis tends to be more painful than itchy.
  • Irritant contact dermatitis often affects hands that have been exposed by resting in or dipping into a container (sink, bucket, tub) containing the irritant.
  • Once a reaction starts, it may take as long as four weeks to resolve completely.
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