Contact allergy, or allergic contact dermatitis, is an itchy rash caused by an allergic reaction to something that touches the skin, such as a metal, fragrance, preservative, hair dye or rubber chemical.
Because the rash can appear a day or two after contact, the cause is often hard to pin down. Patch testing can identify it, so you know exactly what to avoid.
Patch Testing
Patch testing is the test for contact allergy. You will first see one of our consultant dermatologists, who will decide whether you need it and which substances to test. Your patch testing is then planned and read by Dr Ling Li or Dr Catriona Wootton, with our nursing team applying the patches.
Symptoms of Contact Allergy
Allergic contact dermatitis usually causes:
- an itchy red rash, sometimes with small blisters or weeping
- dry, thickened or cracked skin if contact continues
- a rash where the substance touched the skin, such as the earlobes (earrings), wrists (watch straps), eyelids (nail varnish or cosmetics) or hands
- a rash that can spread beyond the area of contact
The rash usually appears 24 to 72 hours after contact, and settles once the cause is avoided.
Causes of Contact Allergy
Common causes include:
- metals, especially nickel in jewellery, buckles and fastenings
- fragrances in perfumes, toiletries and household products
- preservatives in creams, cosmetics, shampoos and wet wipes
- hair dye (PPD) and temporary “black henna” tattoos
- rubber chemicals in gloves and footwear
- acrylates in gel and acrylic nails
- some medicated creams, including antibiotics, antiseptics and occasionally steroids
Contact allergy is different from irritant contact dermatitis, which is caused by repeated contact with water, soaps, detergents or chemicals damaging the skin, and is not an allergy. Many people have both; see our dermatitis page.
Diagnosis of Contact Allergy
Your consultation starts with a detailed history and examination: where the rash is, when it started, your work and hobbies, and the products you use.
If a contact allergy is suspected, your dermatologist will refer you for patch testing with Dr Ling Li or Dr Catriona Wootton. This is the only reliable way to diagnose a contact allergy; skin prick and blood tests do not detect it.
Treatment at Derma for Contact Allergy
Treatment may include:
- identifying and avoiding the cause, with written information on where it is found and safe alternatives
- emollients and soap substitutes to repair the skin barrier
- steroid creams or ointments to settle the rash
- treatment for any irritant dermatitis at the same time
- tablets or phototherapy for severe or persistent dermatitis
Further reading: Patient leaflet from the British Association of Dermatologists
Frequently Asked Questions
Do I need a consultation before patch testing?
Yes. You need to see one of our consultant dermatologists first, who will decide whether patch testing is needed and which substances to test.
Can I become allergic to something I have used for years?
Yes. Contact allergy can develop at any time, even to a product or metal you have used without problems for many years.
Is contact allergy the same as food allergy?
No. They are different types of allergy and are tested differently. Patch testing only detects contact allergy; food allergy is investigated with skin prick or blood tests. See our food allergy page.
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