Contact allergies and patch testing

Written by: Professor Andrew Wright
Published: | Updated: 06/07/2023
Edited by: Emma McLeod

Having a contact allergy to chemicals and products is a frequent problem. These allergies can affect anyone and usually make themselves known with a form of eczema.


Professor Andrew Wright is a consultant dermatologist who specialises in contact allergies and patch testing among many other aspects of his field. In this article, he explains how the causes of contact allergies can be identified. 

A close up of a person's bare skin between the neck and shoulder. A person's hand is resting on it.

What causes contact allergies?

Many materials can cause allergic reactions. The following are common examples:


  • Fragrances
  • Preservatives
  • Hair dyes
  • Metals such as nickel and cobalt
  • Chemicals used in the manufacture of products, such as chemicals made for rubber gloves


How can the cause be identified?

Sometimes, the cause of the problem is obvious such as when the allergic reaction is due to a new product. It can also be obvious when the site of the reaction is very specific such as on the ear: this is very likely caused by nickel in earrings.


Other times, determining the cause is more complex. For instance, hair products might cause a reaction on the scalp but also cause issues and irritation to the upper body and arms as it is washed onto these areas. With such products, it is possible to react to a number of different ingredients; not only the active ingredients in the product itself but also preservatives and fragrances – there are many possibilities.


If it is not obvious what the cause of the problem is then a health care professional may advise patch testing.


What is patch testing?

Patch testing is done at specialised centres and consists of applying standardised materials to the back or to a similar location of the body. Usually, these are left on for two days and then a first reading is performed. A second reading is usually performed two days later. The results are generally reliable and reproducible.


That is to say, the same reaction will happen each time you are tested for a particular chemical. Reactions, however, can be subtle and some people develop irritant reactions which can make interpreting the tests complex and specialised. Occasionally, if you are very allergic to a material, the reaction test site may persist for several days but this generally does not cause serious problems. If your specialist feels that patch testing is needed then this is likely to be booked a few weeks in advance.


Patch testing may be unhelpful if the skin is inflamed. Some patients might need to have their patch testing delayed until a more suitable time:


  • Patients who have recently had significant sun exposure
  • Pregnant women
  • People who have used topical or oral steroid tablets recently


It’s important to let your specialist know if you fit any of these categories as you may not get a positive reaction when tested.


If you or someone you know is suffering from skin allergies, don’t delay in discovering the cause. To book a consultation with Professor Andrew Wright, visit his Top Doctors profile today. 

By Professor Andrew Wright

Professor Andrew Leslie Wright is a consultant dermatologist in Bradford and Leeds who specialises in eczema, psoriasis, skin cancer and skin allergies.

Having decided on specialising in dermatology, Professor Wright gained as much medical experience as possible by working in an infectious diseases unit, in chest medicine, cardiology and endocrinology. He spent six months working on a coronary care unit and six months in a casualty department where he gained experience with a wide variety of practical procedures.

Professor Wright spent six months in the Rupert Hallam Department of Dermatology, Sheffield as part of a medical rotation. He then spent 20 months in the University Department of Dermatology, Royal Infirmary, Edinburgh.

Professor Wright is committed to teaching undergraduate medical students both in the outpatient clinic and on formal lecture courses. He supervises students doing special study modules and examines Leeds University medical students. He is an honorary visiting professor at Bradford University and a member of the Centre for Skin Sciences at Bradford University.

He has appeared on television, both live and recorded, on numerous occasions and has performed many radio interviews, particularly with regards to sun awareness and skin cancer. He has most recently contributed to two episodes of the Channel 4 programme Embarrassing Bodies.

Professor Wright is a member of several professional societies, including the British Association of Dermatologists, European Contact Dermatitis Society, British Society for Investigative Dermatology and British Hair and Nail Society.

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