Contact allergies and patch testing

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- both obvious and unclear causes.

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 (a rash, for example) 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. Click here to find out how Professor Wright can help you with patch testing and more.