Allergy Skin Tests
Overview
Allergy skin tests help identify certain substances that trigger allergic reactions. During these tests, healthcare providers place allergens on the skin and watch for any response, such as redness or swelling.
This process, together with a person’s health history, can detect what may be causing allergy symptoms. Common allergens include:
- Pollen
- Pet dander
- Foods
- Dust mites
Purpose of Allergy Skin Testing
These tests help determine which specific allergens are responsible for a person’s allergic reactions. Common triggers include environmental allergens (like pollen, dust mites, and pet dander), certain foods, penicillin, and insect venom.
Knowing the exact cause of an allergy allows for a personalized management plan. Doctors use the results to diagnose and manage conditions such as:
| Condition | Allergens Often Involved |
|---|---|
| Hay fever | Pollen, dust mites, pet dander |
| Allergic asthma | Dust mites, pollen |
| Eczema | Food, environmental allergens |
| Food allergies | Peanuts, milk, eggs, shellfish |
| Penicillin allergy | Antibiotics |
| Insect sting allergy | Bee venom |
They may also help uncover less common allergy-related issues, such as chronic hives or certain types of sinus conditions. Most people, including children and infants, can safely undergo skin testing.
Who Should Not Have Skin Tests
Some people may not be able to have allergy skin tests. For example:
- Those who have had a severe allergic reaction in the past, since even small amounts of allergens might cause a serious reaction called anaphylaxis.
- People who take certain medicines, such as antihistamines, some antidepressants, and heartburn medicines. These can stop the test from working as well.
- Those with certain skin problems, including severe eczema or psoriasis, since there may not be enough clear skin for testing. Other conditions like dermatographism may make test results unreliable.
Alternatives to Skin Tests
Skin testing is especially helpful for detecting allergies to airborne substances such as pollen, pet dander, and dust mites. It can also assist with food allergies, although additional or follow-up tests may be needed since food-related reactions are often more complex.
If skin testing isn’t suitable, a blood test that checks for allergy-specific antibodies can be used instead. However, blood tests are not typically reliable for diagnosing penicillin allergy.
Possible Side Effects
Skin testing can cause small, itchy red bumps (wheals) during or after the procedure. These may last for a few hours to a couple of days. Some people also experience localized swelling and redness around the test area.
Although rare, serious allergic reactions can occur. Clinics ensure testing is performed under the supervision of trained professionals who can respond quickly if needed. People with asthma may be more likely to have stronger reactions.
Common Issues
| Side Effect | Symptoms | How Long It Lasts |
|---|---|---|
| Skin swelling | Redness, itch | Few hours to days |
| Wheals | Bumps, itch | Up to a few days |
Rare Risks
- Severe allergic reaction
- More severe symptoms in people with asthma
How You Get Ready
Many types of medicine can affect skin allergy testing and make results less reliable. Before the test, it’s important to give your healthcare provider a list of all the medicines you take, including both prescription and over-the-counter drugs.
This step helps avoid mistakes and keeps you safe. Some medications can block normal allergic reactions, making test results unclear. Others may increase the risk of a stronger allergic response during testing.
To reduce these risks and improve accuracy, doctors often ask patients to stop certain medications before the test. The amount of time you need to stop taking a medicine depends on how long it stays in your system.
| Type of Medicine | How Long to Stop Before Testing |
|---|---|
| Prescription antihistamines | Up to 10 days |
| Nonprescription antihistamines | Up to 10 days |
| Tricyclic antidepressants | Ask your healthcare provider |
| Heartburn medicines | Ask your healthcare provider |
| Asthma medicine | May affect results for 6 months or more |
If you’re not sure whether your medicine could affect allergy testing, talk with your healthcare provider for clear instructions. Never stop or change any medications without their guidance.
What You Can Expect
Skin Prick Allergy Testing
Doctors often use skin prick testing to find out if someone reacts to certain substances, like pollen, pet dander, or food. In this test, the doctor gently places tiny drops of possible allergens on the skin—usually on the forearm for adults or the upper back for children.
A special tool called a lancet is then used to prick the skin, helping the allergen go just under the surface. This step is quick and may feel like a light scratch, but it usually does not hurt.
Each allergen is applied with a new lancet. Bleeding is rare, and most people only feel mild discomfort that goes away quickly. In addition to the allergens, two control substances are also used. Histamine is applied to check whether the skin is reacting normally.
If the skin doesn’t respond to histamine, it may be harder to interpret the results. Glycerin or saline is also tested, as they typically do not cause a reaction. If the skin does react to these, the person may simply have sensitive skin.
Typical Steps
- The skin is cleaned with alcohol.
- Spots are marked for different allergens.
- Drops of test substances are placed on the skin.
- The skin is lightly pricked with a lancet.
- After about 15 minutes, the doctor looks for red, raised marks.
- The area is cleaned off.
If a person is allergic, a red, itchy bump will show up where the allergen was placed. The bumps are measured to decide which things are causing reactions.
Intradermal Allergy Testing
Doctors sometimes use a different method when a stronger or more sensitive test is needed. This approach involves injecting a very small amount of allergen just below the surface of the skin, usually on the arm. This is called an intradermal test.
Intradermal testing is often used when checking for allergies to things like insect stings or penicillin. The needle is very thin, so the pain is minimal—though the pinch may feel slightly stronger than with a skin prick test.
After the injection, healthcare staff monitor the area for about 15 minutes. If redness or a raised bump appears, it may indicate an allergy to the tested substance.
Allergy Patch Testing
Patch testing looks for delayed allergic reactions, usually caused by substances people come into contact with in daily life. This test helps identify whether products like perfume, soap, metal, or hair dye are causing problems.
Instead of using needles, healthcare providers place small patches containing tiny amounts of possible irritants on the back or arm. Typically, 20 to 30 substances are tested at the same time. The patches remain on the skin for 48 hours. During this period, it’s important to:
- Keep the patches dry.
- Avoid heavy exercise.
- Wear loose clothing.
The patches remain on the skin for 48 hours. During this period, it’s important to avoid getting the area wet or doing activities that cause heavy sweating. After two days, the person returns to the clinic to have the patches removed.
The doctor then checks for any redness or swelling that may indicate an allergic reaction. Because some reactions take longer to appear, a follow-up check-up might be needed a few days later.
Test Outcomes
Skin prick and intradermal test results are usually available right away, while patch test results may take a few days, since reactions can develop more slowly. A positive result suggests that the person could be sensitive to a specific substance.
The size of the wheal—a raised bump at the test site—can give clues about how strong the allergy is. Larger bumps often indicate a higher level of sensitivity. A negative result generally means the person is probably not allergic to that item.
However, allergy skin tests are not perfect. Sometimes, people react to a substance during testing even if they’re not truly allergic—a false positive. In other cases, someone who is allergic may not react—known as a false negative.
Test results can also vary from time to time, even for the same person. Based on the test results, an allergy specialist may recommend:
- Medication
- Allergy shots (immunotherapy)
- Making changes at home or work
- Diet adjustments
Patients should feel comfortable asking their specialist questions about what the results mean and what steps to take next in their care.
