Contact allergy is an allergic skin reaction from contact with a substance that is usually harmless to others.

The commonest manifestation is an itchy rash that develops over a few days, after skin contact with a substance. The affected area first becomes itchy, then red and swollen with vesicles (water bubbles).

Although usually confined to the area of contact, sometimes strikingly so the rash can spread to other parts of the body.
occasionally the rash is more chronic, manifesting as an itchy patch that does not heal for weeks or even months. This usually occurs when there is frequent contact with the substance e.g. a watch strap. The rash resulting from contact allergy is called allergic contact dermatitis.

A substance that can cause contact allergy is called a contact allergen. Common contact allergens are:

• metals e.g. nickel in watch straps, chrome in cement


• skin care products e.g. fragrances, lanolin


• medication e.g. flavine, neomycin.

A skin test called a patch test is used to confirm contact allergy. The upper back is used as a test site. A small amount of the suspected contact allergen (diluted to a non-irritant concentration) is applied onto the skin in an aluminium chamber and sealed with hypoallergenic tape. Usually, several suspected allergens are tested simultaneously. They are left on the skin for 48 hours and read at 48 and 96 hours. A positive reaction indicates that he patient is allergic to the test substance. This is a very safe procedure.

In many cases, removing the cause i.e. the allergen from skin contact will result in a cure. Usually, once allergy to a substance has developed, it remains for life. That is to say, future contact with the substance will result in an allergic contact dermatitis again. This is exactly like a drug allergy. It is advisable for patients to carry a card to remind themselves and their doctors of their contact allergy.