Allergic Contact Dermatitis

What is contact dermatitis?

Dermatitis, also called eczema, means inflammation of the skin. Contact dermatitis is dermatitis caused by something that comes into contact with the skin. It is common and can have a significant effect on daily life, work and wellbeing.

There are two main types: irritant contact dermatitis and allergic contact dermatitis. They can look very similar, and some people have both.

Who gets it?

Contact dermatitis is common and can affect anyone. Irritant contact dermatitis is more likely in people who have had eczema and in people whose work involves frequent wet work or contact with chemicals, such as cleaners, cooks, hairdressers, beauticians, florists, gardeners, metal workers and healthcare workers. Allergic contact dermatitis can develop at any age, including to products that have been used for years without any problem.

What causes it?

Contact dermatitis is caused by contact with a substance that either irritates the skin directly or triggers an allergic reaction.

Irritant contact dermatitis

Irritant contact dermatitis happens when a substance directly damages the outer layer of the skin. It does not involve an allergy. It usually develops after repeated contact over a period of time, and the risk depends on how often and how long the skin is exposed and how strong the substance is.

Common causes include water, soaps, detergents, cleaning products, solvents such as petrol, oils, cutting fluids and frequent hand washing. The hands are most often affected. People working as cleaners, cooks, hairdressers, beauticians, florists, gardeners, metal workers and healthcare workers are at higher risk, as are people who have had eczema.

Allergic contact dermatitis

Allergic contact dermatitis happens when the immune system becomes sensitised, or allergic, to a particular substance, called an allergen. Once someone is sensitised, the skin becomes inflamed each time it is in contact with that substance again. The reaction usually appears hours to a few days after contact, which can make the cause hard to spot.

Common allergens include nickel and cobalt in jewellery, buckles and fastenings; fragrances; preservatives in cosmetics, skincare, shampoos and wet wipes; hair dye; acrylates in gel and acrylic nails and some adhesives; rubber chemicals in gloves and shoes; chromate in cement and leather; plants; and ingredients in medicated creams, including some antiseptics and antibiotics. Sensitisation can develop to something that has been used for years without a problem.

Is it hereditary or contagious?

Irritant contact dermatitis is more likely in people with an inherited tendency to eczema, asthma or hay fever. Allergic contact dermatitis is not usually inherited.

Contact dermatitis is not contagious. If the skin becomes infected, however, it can develop impetigo, a contagious bacterial infection that needs treatment.

What does it look and feel like?

Allergic contact dermatitis typically begins as an itchy rash, which may then swell, blister and ooze before turning scaly. Irritant contact dermatitis more often causes burning, stinging, soreness and dryness, with cracks and splits. With repeated exposure, either type can lead to thickened, leathery skin.

On lighter skin the rash looks red. On brown and black skin it may look purple, dark brown or grey, and can leave darker patches as it settles.

The hands are the most commonly affected area, but contact dermatitis can occur anywhere. The site often gives clues to the cause: the earlobes and wrists with jewellery, the eyelids and face with cosmetics or nail products transferred by the fingers, the scalp and hairline with hair dye, and the feet with shoes.

How is it diagnosed?

Irritant contact dermatitis is diagnosed from the history and appearance of the rash, taking into account your job, hobbies and the products you use.

Allergic contact dermatitis is diagnosed with patch testing. Small amounts of common allergens, along with any relevant products of your own, are applied to the back on special patches. The patches stay on for two days and the skin is then checked over the following days for any reaction. Patch testing identifies the specific substances you are allergic to, so that you can avoid them. It is different from the skin prick tests and blood tests used for hay fever and food allergies.

What is the outlook?

There is no cure for a contact allergy, and once you are sensitised to a substance you usually remain so. However, if the cause is identified and avoided, allergic contact dermatitis often improves significantly or clears completely. Avoiding some common allergens can be challenging, so knowing exactly what to look for on ingredient labels is important. Irritant contact dermatitis improves as the skin is protected from irritants, though this can take several months.

More information

British Association of Dermatologists patient leaflet: https://www.bad.org.uk/pils/contact-dermatitis

This page gives general information only and is not a substitute for a consultation. Everyone's skin is different, and what is right for you will depend on your own circumstances. If you are worried about a skin problem, please book an appointment with Dr Mounsey or speak to your GP. If you have a mole or skin lesion that is changing, bleeding or growing quickly, please seek medical advice promptly.