Skin Prick Allergy Test: Purpose, Procedure, and What to Expect

What is a skin prick allergy test?

A skin prick test (also known as a scratch test) is a diagnostic procedure that helps find out what substances may be responsible for your allergic reactions. For this test, your skin is tested with a small amount of possible allergens to monitor how your body reacts.

This test is commonly used to check for:

• Pollen and dust allergies

• Food allergies (like nuts, eggs, or milk)

• Pet dander allergies

• Insect sting allergies (like bees or wasps)

This test is one of the fastest and least painful ways to obtain invaluable insights into your allergies, which in turn can guide your doctor on how best to treat and prevent allergic reactions.

Why do I need a skin prick test?

A skin prick test can help determine whether an allergy is responsible for your symptoms. If you have asthma symptoms that are hard to control or signs of an allergic reaction, your doctor may recommend this test.

It is most helpful when you have:

• Persistent sneezing, runny, or stuffy nose

• Itchy, red, or watery eyes

• Skin issues, such as hives or eczema

• Shortness of breath or difficulty breathing, either at rest or during activity

• Potential reactions to specific foods

The test’s also used sometimes after a severe allergic reaction known as anaphylaxis. This reaction can happen very fast and affect your breathing. Knowing your triggers is important to help prevent it from happening again.

By identifying the substances that are causing your symptoms, the test helps your healthcare provider create a clear plan to manage or treat your allergies more effectively. 

How does a skin prick test work?

A scratch test works by introducing tiny amounts of substances that may cause allergic reactions (known as allergens) into the surface of your skin to see how your immune system responds.

Here’s how the process typically works:

• Preparation:

  • After cleaning your forearm or upper back, your doctor will make small marks on the skin to indicate the locations of each allergen.

• Application of allergens:

  • A drop of each allergen is placed on the skin. These might include common triggers like pollen, dust mites, pet dander, certain foods, or insect venom.

• Pricking the skin:

  • Gently prick each designated mark on your skin using a small, sterile lancet. This method allows a tiny amount of the allergen to enter just under the skin's surface.

  • The pricks are not deep and usually feel like a light scratch.

• Observation:

  • Once the allergen has been applied to the skin, your healthcare provider will observe it for any reaction for about 15 to 20 minutes.

• Reading the results:

  • If you are allergic to one of the substances, you may develop a small raised bump, similar to a mosquito bite, at the test site.

  • The size of the bump is then measured to help assess the severity of the reaction.

This test helps your doctor identify which allergens may be causing your symptoms and is an important step in developing an effective treatment or allergy management plan. 

Types of allergy skin tests

There are several types of allergy skin tests. Your doctor will choose the most suitable one based on your symptoms and medical history.

Skin prick test

This procedure is the most common type of allergy test. It involves:

• Cleaning the skin, usually on your forearm or upper back

• Marking small spots where the allergens will be placed

• Using a tiny tool (lancet) to gently prick the skin through a drop of each allergen

• Watching for a reaction, like redness, itching, or a small elevated bump, within 15 to 20 minutes

Intradermal test

This test is used if the results of the skin prick test  are unclear or if your doctor still suspects an allergy:

• A small amount of allergen is injected just under the surface of your skin using a fine needle.

• The area is then monitored for signs of a reaction.

Patch test

Your doctor will use this test to look for delayed allergic reactions, particularly those that lead to skin conditions like contact dermatitis.

• Patches containing small amounts of different allergens are placed on your back.

• You wear the patches for about 48 hours.

• The skin is then checked over several days to see if any reaction occurs.

If you're experiencing symptoms like persistent sneezing, itchy eyes, skin rashes, or breathing difficulties, it may be time to consider allergy testing. A skin prick test can help identify the cause and guide your treatment. Request an appointment with Thomson Medical today to consult with a specialist for tailored care.

How to prepare for testing?

To get the most accurate results from your allergy test, it’s important to follow a few simple steps before your appointment:

• Stop taking antihistamines at least 3 to 7 days before the test, or as advised by your doctor. These medicines can affect the test results.

• Avoid using creams, lotions, or perfumes on the area where the test will be done (usually your forearm or back), as they may interfere with how your skin reacts.

• Tell your doctor about any medications you’re taking, including prescription drugs, over-the-counter medicines, and herbal supplements. Some medications may affect the test results or increase the risk of side effects.

Your healthcare professional will guide you through any additional instructions specific to your situation.

What to expect during and after the test?

The test involves placing small amounts of allergens on your skin using tiny pricks. It’s quick, generally painless, and carried out under medical supervision.

After the test, the allergens may cause mild skin reactions. Such reactions can include small, raised bumps or redness. These usually fade within minutes, but in some cases, they may last for a few hours or, rarely, a couple of days.

You may also have mild allergy symptoms, such as:

• Watery or itchy eyes

• A runny or blocked nose

• Sneezing

These effects are temporary and usually settle on their own. Your doctor will advise you when it’s safe to restart any allergy medicines you paused before the test.

What can you expect from your skin allergy test results?

When will you get your results?

• For skin prick and intradermal tests:

  • You'll receive your results right away, while you're still at your healthcare provider's office

• For patch testing:

  • Results typically take about four days to develop

What do the results mean?

Your results will fall into one of two categories:

• Positive:

  • This means you’re likely allergic to a certain substance. If the raised bump (called a wheal) on your skin is large, it usually suggests you’re more sensitive to that allergen.

• Negative:

  • A negative result means it’s unlikely that you’re allergic to that substance.

If you do have an allergy, your healthcare provider will guide you through the next steps.

What about false results?

It’s important to know that skin allergy tests aren’t always 100% accurate. Occasionally the results don’t match your real-life reactions.

• False-positive result:

  • You react to a substance during testing but don't have reactions when encountering it in everyday life

• False-negative result:

  • You don't react during testing but do have reactions when encountering the substance outside the medical setting.

If your healthcare provider has concerns about the accuracy of your results, they may recommend additional testing to confirm your diagnosis.

Are skin prick tests safe?

Yes, skin prick testing is a safe and commonly used method for identifying allergies in both adults and children. Due to its affordability, speed, and minimal discomfort, it stands as one of the most trusted kinds of allergy skin testing.

The procedure involves exposing your skin to various allergens to observe how your body reacts.

Most people experience only mild, temporary effects such as slight redness, itching, or swelling at the test site. These typically appear within a short period of time—usually 15 to 20 minutes—and settle soon after.

Although rare, some individuals may experience a stronger reaction during testing. For this reason, allergy exposure is carefully controlled, and testing is always performed by a trained medical professional in a clinical setting.

This process ensures that if a more serious reaction, such as anaphylaxis, occurs, it can be managed immediately and safely.

If you experience any unusual symptoms or feel unwell during or after the procedure, please notify your healthcare team promptly.

FAQ

What is a skin prick test?

Skin prick testing is a common method used in allergy assessment. It involves placing a small amount of a suspected allergy-causing substance onto your skin (usually the forearm or back) and gently pricking the surface. If you are allergic, you may develop a small raised bump, similar to a mosquito bite, at the site.

This test helps your doctor quickly identify which allergens are causing your symptoms and how sensitive you are to them.

What are the lists of allergens for the skin prick test?

The list of allergens tested depends on your health history, symptoms, and environment. Common allergens include:

• Pollens from trees, grasses, and weeds

• Dust mites

• Pet dander (from cats, dogs, and other animals)

• Mold spores

• Foods like milk, eggs, peanuts, shellfish, soy, and wheat

• Insect venom from bees, wasps, or fire ants

Your doctor will select the specific allergens to test based on your symptoms and medical history.

Which is better, a skin prick or a blood test?

Both types of allergy testing have their benefits. Here's how they compare:

Skin prick testing

• Considered the gold standard for allergy testing.

• Provides immediate results during your appointment.

• Helps assess your level of sensitivity to each allergen.

• Usually more affordable.

• Tests many allergens at once.

Blood tests

• Blood test is useful if you have a common skin condition (like eczema) that may interfere with skin testing.

• Can be performed even if you're taking antihistamines.

• May be preferred if you’ve had a severe allergic reaction in the past.

Your doctor will recommend the best method based on your symptoms and health conditions.

What if I test negative for allergies but still have symptoms?

If your skin prick test comes back negative but you're still experiencing symptoms, it could mean:

• Your symptoms are caused by a non-allergic condition

• You may have a sensitivity that doesn’t show up on standard allergy skin testing (such as a non-IgE-mediated reaction)

• The specific allergen causing your symptoms wasn't included in your test

Your doctor may recommend additional tests or evaluations to determine the cause of your symptoms and prevent a false allergy diagnosis.

How do the results from a skin prick test show my level of sensitivity?

When you undergo skin prick testing, the size of the reaction (wheal and flare) on your skin indicates your degree of sensitivity to each allergen.

A larger reaction typically suggests a stronger sensitivity, which helps your doctor understand how severely you might react when exposed to certain substances in everyday life. This information is essential for developing your personalised allergy treatment plan.

Can my allergies change over time, requiring new testing?

Yes, your body's response to allergens can change throughout your life:

• Some allergies may become less severe or disappear completely.

• New allergies can develop at any age.

• Environmental changes, like moving to a new location, can expose you to different allergens.

• Major life events like pregnancy or serious illness can sometimes affect your immune system's responses.

For these reasons, your doctor may recommend periodic allergy skin testing as part of ongoing health condition management. Updated testing ensures your treatment plan remains appropriate for your current allergy assessment.

The information provided is intended for general guidance only and should not be considered medical advice. For personalised recommendations and tailored advice, please consult a specialist at Thomson Medical. Request an appointment with Thomson Medical today.