How Does Patch Testing Work?

Allergies are immune system overreactions, where the body responds to benign substances as though they could harm it. When it comes to the skin, allergies and sensitivities usually result in a rash. 

Allergic reactions aren’t always instant, and in the case of skin rashes, your body’s response to an allergen may be delayed. 

At Allergy Associates of Utah, we use patch tests to measure your response to common and uncommon contact allergens. Unlike scratch tests, which show reactions in minutes, patch tests remain in place for several days. 

There are over 15,000 substances that cause allergic skin reactions. Patch tests help us narrow the field when the allergen isn’t obvious. Here’s what you need to know about how patch testing works. 

A comprehensive test

With so many potential allergens, testing one at a time is not practical. Instead, we test for a range of candidates. Some of the more common categories and substances include:  

• Cleaning agents
• Detergents
• Fragrances
• Hair dyes
• Latex
• Metals
• Preservatives
• Resins

We place a small amount of a substance to be tested onto a patch, which we then apply to your skin, often on the back. After 48 hours, we’ll evaluate your skin’s reaction to each patch to determine your active allergens. 

Interpreting the results

After completing your patch test, you’ll better understand how to prevent allergic skin rashes in the future. We’ll help by sharing our experience and knowledge about common products and other sources of the allergens you need to avoid. 

These include household products, personal care items like soaps and shampoos, and substances you might expect to encounter in your typical day. Avoiding these can reduce your chances of additional rash outbreaks. 

What to expect from your patch test

Once the patches are in place, you may begin to react to one or more of them. That patch might feel itchy or uncomfortable, but leaving it in place is important for the most accurate interpretation of your skin sensitivities. 

Don’t bathe or shower while wearing the patches since getting them wet can alter your results. Removing or loosening them can also invalidate the patch test. 

After two days of wearing the patches, we'll see you for an initial assessment. Depending on the results, we may see you again within a week since some allergic responses take longer to develop. 

Contact dermatitis

Many substances, such as chemicals you may be exposed to through your job or perhaps a hobby, can cause contact dermatitis after repeated exposure. If your initial patch test shows no allergens, we may recommend an expanded patch test or one specific to your industry. Expanded tests can pinpoint about 80% of allergens. 

Contact Allergy Associates of Utah when you suspect allergies are behind your skin rash. We’ll examine your condition and prepare you for a patch test when required. Call or click to book an appointment with our nearest location today.