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Allergic contact dermatitis

ivy allergyAllergic contact dermatitis is a rash that happens when your skin comes into contact with something you are allergic to (this is called an allergen).

Allergic contact dermatitis is different to irritant contact dermatitis. Irritant contact dermatitis can affect anyone. However, you will only get allergic contact dermatitis if you are allergic to certain things that touch your skin.

You are not born with the allergy that causes your contact dermatitis and it doesn't happen the first time you come into contact with the allergen. You may have had contact with it once or even many times before you become allergic to it. Doctors don't know why this happens for some people but not others, or why you may suddenly develop an allergy to something you've had a lot of contact with before.

What can cause it?

Many things can cause allergic contact dermatitis. Some common ones include nickel (in a lot of jewellery), rubber (latex), hair dyes, some plants (such as ivy), and chemicals in make-up, soap, skin-care products, and plasters.

What are the symptoms?

If you have allergic contact dermatitis you will develop an itchy rash after coming into contact with the allergen. This usually happens a few hours afterwards, not within a few minutes like hives do. Your skin can become red, sore and swollen. This will settle down after a few days, as long as your skin is no longer in contact with the allergen.

Usually the rash happens where the allergen has touched your skin, for example on your eyelids if it is a chemical in your make-up or skin-care products, or under your watch strap if you are allergic to nickel.

Do I need any tests?

If it's obvious what's causing the rash you won't need any tests. However, if it's not clear what's causing the problem, then you might be referred to see a dermatologist (skin doctor) for patch testing.

During a patch test small amounts of several possible allergens are put on your skin (usually on your back) and covered over with a dressing. After a couple of days these dressings are removed to check which ones have caused an allergic reaction on your skin. You can read more detailed information about patch testing on DermNet.

If you think make-up or your skin-care products are causing the problem then you can test them at home with a simple test (called the open user test). Put the product on to a small area of sensitive skin (such as the inside of your upper arm) twice a day for five to 10 days in a row. If you get a rash in that area, it's likely you have allergic contact dermatitis. This is a useful way to check your own make-up or skin-care products so you can stop using anything that causes problems.

How is it treated?

The main treatment for allergic contact dermatitis is to avoid contact with whatever you are allergic to.

Using moisturisers (also called emollients) on any affected area will help to rehydrate your dry skin and also provide a barrier that helps your skin to heal. A mild steroid cream like 1% hydrocortisone, which you can buy from a pharmacy, may help it to settle down more quickly.

See your GP if the rash is severe, affecting a large area, or if it doesn't improve with the hydrocortisone cream after a few days. You might need stronger steroid creams or even steroid tablets (prednisone) to settle down the redness and itch.

If even treatments from your GP don't work then you may be referred to see a skin doctor for other treatments such as phototherapy, or for stronger medications that suppress your immune system (which is involved in any allergic reactions).

Written by HealthInfo clinical advisers. December 2016.

Sources

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Review key: HICOD-326084