Skin prick tests

Are you sniffing and sneezing all the time? Do you experience skin irritations? Or problems when you eat certain foods? Would you like to find out what could be causing these symptoms? Think it might be an allergy?

Skin prick tests are one of the most common ways to diagnose what you are allergic to. Let’s take a look at how skin prick tests for allergy are done and what the results of a skin prick test can mean for you.

What is a skin prick test?

A skin prick test is one of the most common diagnostic tools for people with allergy. It doesn’t mean you have skin allergy. Your skin is simply used as a canvas for the test.

Even though you might have symptoms in your eyes, nose, lung or gut, a skin prick test can still show a reaction to your triggers. And the reaction on your skin can then be measured and compared.

Skin prick tests are done when allergy is suspected. A skin prick test may help to identify the triggers, or allergens that could be causing your allergy symptoms. Information from a skin prick test can help your doctor develop a treatment plan for your allergy.

When should a skin prick test be done?

If your allergy symptoms are mild and the cause is obvious, your health care provider will be able to offer advice and discuss treatment options with you.

But you may be referred for a skin prick test if your symptoms are more severe or it’s not clear what’s causing them. The results of a skin prick test must be analyzed by a health care provider alongside your medical history and symptoms.

Skin Prick Tests

Are you sniffing and sneezing all the time? Do you experience skin irritations? Or problems when you eat certain foods? Would you like to find out what could be causing these symptoms? Think it might be an allergy?

Skin prick tests are one of the most common ways to diagnose what you are allergic to. Let’s take a look at how skin prick tests for allergy are done and what the results of a skin prick test can mean for you.

What is a skin prick test?

A skin prick test is one of the most common diagnostic tools for people with allergy. It doesn’t mean you have skin allergy. Your skin is simply used as a canvas for the test.

Even though you might have symptoms in your eyes, nose, lung or gut, a skin prick test can still show a reaction to your triggers. And the reaction on your skin can then be measured and compared.

Skin prick tests are done when allergy is suspected. A skin prick test may help to identify the triggers, or allergens that could be causing your allergy symptoms. Information from a skin prick test can help your doctor develop a treatment plan for your allergy.

When should a skin prick test be done?

If your allergy symptoms are mild and the cause is obvious, your health care provider will be able to offer advice and discuss treatment options with you.

But you may be referred for a skin prick test if your symptoms are more severe or it’s not clear what’s causing them. The results of a skin prick test must be analyzed by a health care provider alongside your medical history and symptoms.

Skin prick tests explained in 4 simple steps

Step 1

Your skin is marked with a grid

Step 2

A drop of each allergen is applied to an area on the grid

Step 3

The skin under each drop is gently pricked

Step 4

After 15 to 20 minutes any skin reactions can be analyzed

Skin prick tests explained step by step

Skin prick testing usually takes place at an allergist’s office. So you can know what to expect if you’re referred for a skin prick test for allergy, we’ll walk you through the process and explain all the details.

Step 1: Your skin is marked with a grid

First, your skin will be prepared for the test. Usually the skin of the underside of your forearm will be used. The skin of your back can also be used, which may be a better option for small children. Your health care provider will mark out a grid on your skin or use a numbered tape. This allows each allergen that will be tested to have its own area on your skin.

Step 2: A drop of each allergen is applied to an area on the grid

Next, a series of allergens will be tested. A drop of each allergen to be tested will be placed on the skin.

In addition to the drops of allergens, two control drops will be applied. A control test makes sure that the results of the skin prick test are valid.

The positive control substance for a skin prick test for allergy is histamine. Histamine is one of the chemicals your body produces when you have an allergic reaction. A drop of histamine is placed on one side of the control area of the grid on your skin. A negative control test is placed on the other side of the control area. The negative control substance is a drop of the test liquid with no allergen or histamine.

Doing the control tests means your skin’s reaction to histamine and the physical act of being pricked can be compared to reactions triggered by the tested allergens.

Skin prick tests are done when allergy is suspected. A skin prick test may help to identify the triggers that could be causing your allergy symptoms.

Step 3: The skin under each drop is gently pricked

The top layer of your skin under each drop is gently pricked with a lancet, so that the allergen is introduced into the skin. If correctly administered, a skin prick test doesn’t cause bleeding. For most people skin prick testing isn’t painful, but it could feel a little uncomfortable or itchy.

Step 4: After 15-20 minutes any skin reaction can be analyzed

The skin-pricking part of the test lasts about ten minutes. Once it’s complete, you’ll need to wait for a further 15 to 20 minutes before the results can be analyzed. The control spot will be checked to make sure the results are valid. Each spot of skin tested will be checked for a reaction.

If there is a reaction it’ll be characterized by a small, red, itchy, bump of skin similar to a mosquito bite. This is called a wheal, surrounded by a flare. Each wheal and flare reaction on your skin will be measured across the longest diameter. Wheals that measure 3mm or more are generally positive. Wheals less than 3mm in diameter are considered negative.

What do your skin prick test results mean?

No reaction on the tested spot of skin or a wheal that is less than 3mm in diameter, means a negative skin prick test result. So, allergy to that particular allergen is very unlikely.

Wheals more than 3mm in diameter indicate a positive skin prick test result. A positive skin prick test can imply which allergen or allergens might be responsible for causing your allergy symptoms.

But it is possible to have a positive skin prick test result and not develop allergy symptoms when you are exposed to that allergen.

Sensitised or allergic?
What's the difference?

Wheals more than 3mm in diameter indicate a positive skin prick test result. A positive skin prick test can imply which allergen or allergens might be responsible for causing your allergy symptoms.

But it is possible to have a positive skin prick test result and not develop allergy symptoms when you are exposed to that allergen. This happens in about 15% of people with a positive result. You can be sensitized to an allergen without it causing an allergic reaction. Being sensitized means your immune system has registered the substance as something potentially dangerous, but your body is not triggering full-blown allergy symptoms. You’re not allergic to that trigger. This is why your skin prick test results must always be considered in relation to your symptoms and medical history.

How accurate are the results of a skin prick test?

The overall accuracy of skin prick tests is high. However, the accuracy can be affected by certain medications, such as antihistamines. Ask your health care provider which medication you need to stop taking in the lead-up to your skin prick test.

Sensitised or allergic?
What's the difference?

This happens in about 15% of people with a positive result. You can be sensitized to an allergen without it causing an allergic reaction. Being sensitized means your immune system has registered the substance as something potentially dangerous, but your body is not triggering full-blown allergy symptoms. You’re not allergic to that trigger. This is why your skin prick test results must always be considered in relation to your symptoms and medical history.

How accurate are the results of a skin prick test?

The overall accuracy of skin prick tests is high. However, the accuracy can be affected by certain medications, such as antihistamines. Ask your health care provider which medication you need to stop taking in the lead-up to your skin prick test.

Reactions to a skin prick test

If you find the wheals from the skin prick test too itchy or irritating, tell the doctor or nurse. They might be able to give you something to soothe it after the results have been read, such as a corticosteroid cream. Any reaction usually fades within a few hours.

Skin prick tests are generally well tolerated. In rare cases, skin prick tests can trigger a severe, immediate allergic reaction. That’s why it's important to have skin prick tests performed at an office where appropriate emergency equipment and medications are available.

What to do after skin prick tests

Knowing what you are allergic to means you’re better equipped to manage your allergy symptoms. You’ll be able to discuss your treatment options with your health care provider and make decisions that are right for you.

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