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Private Consultant Dermatologist
Harley Street Dermatology

Skin Conditions

 

How Long Does a Patch Test Take?

A patch test can find out exactly what is causing your skin allergies, but it will take a while for us to work out which allergens are affecting you. You should be prepared to wear the patches for a few days and to visit the skin clinic several times during the patch test.
 
 What is a Patch Test?
 

What is a Patch Test?

Patch tests are a way for us to find out which allergens cause a reaction in your skin. Lots of different allergens will be applied to your skin and covered by sticky patches. Your skin will be marked so that we can tell which allergen was applied to each area. We can then wait and see where any skin allergy symptoms appear. If you develop a rash or other symptoms under a particular patch, then we will know that you are allergic to the substance it contained.

Having the Patch Test

Having a patch test isn’t as quick as having a blood test. You will need to visit your dermatologist several times and keep wearing the patches in between these appointments.

  • First appointment: patches are applied.
  • Second appointment: check for reactions, usually 48 hours later.
  • Follow up appointments: continue monitoring the skin at 2-3 day intervals, depending on your response.
The entire process should take about a week, but sometimes it can be longer. You might need to come in again for additional check-ups or to test new allergens, depending on how your skin reacts.
While the patches are in place, you will need to take care not to dislodge them and avoid swimming and taking baths or showers. However, you should be able to conduct most of your usual activities, so the patch test shouldn’t disrupt your life too much.

Why Do Patch Tests Take So Long?

Although some allergic reactions can appear immediately, it often takes time for the symptoms to develop. You might not have a rash until hours or even days after you came in contact with the allergen. The delay between contact and the symptoms can make it much harder to identify the cause of your allergies. The patch test can overcome this by recording which allergens touched your skin and where. Even if it takes a long time for the symptoms to appear, we’ll be able to identify the cause because we’ll keep monitoring your skin during the patch test.

In most cases, it will take about a week to complete the patch test, but it does depend on your skin. Sometimes it can take a couple of weeks for a result to be seen. If you react quickly, then the patch test can be completed faster. If you experience more delayed reactions, then it can take longer. The patch test will also take more time if you don’t respond to the more common allergens that we test first. We will then need to add new patches to see if you respond to one of the rarer allergy triggers.

However long it takes, the patch test should help us to work out what is causing your allergies. You will then be able to avoid this allergen to prevent your symptoms from returning.

 

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