What kinds of allergy tests are there?

Allergies occur when the human immune system starts fighting substances that are in fact quite harmless, like pollen, dust or foods. The more sensitive the is to a particular substance that triggers an allergic reaction (allergen), the more severe the resulting symptoms are. Allergies may cause watery or red eyes, sneezing attacks, a stuffy nose, an itchy rash or stomach ache. In rare cases an may lead to an anaphylactic shock. Then the airways become narrow, making it very hard to breathe, and there is a severe drop in blood pressure. Anaphylactic shock can become life-threatening if not treated immediately.

Various tests can be used to find out what kind of substance is causing an allergic reaction: skin tests, blood tests and provocation tests. Your doctor will usually decide which test to use based on your description of the symptoms and your medical history.

How are skin tests done?

Skin tests are easy and quick to do, so they are often the test of choice for determining what is causing an . Possible triggers are applied to the skin and the reactions are observed. This is most commonly done on the inside of your lower arm, or sometimes on your back.

Skin prick test

In this test, the doctor puts drops of different watery solutions containing allergens (like pollen or trace amounts of animal hair) on various marked positions on your skin. Your skin is then pricked a little at each site so that the allergens can enter the skin. To test for a food allergy, the food can be pricked first – before pricking your skin.

If you're allergic to the substance, your skin will react: On light-colored skin, the marked site will become red and a small bump (wheal) will appear. Wheals develop on dark skin too, but they're more the color of the surrounding skin or a bit lighter. The skin prick test is mainly used to detect allergies that trigger an immediate reaction when they make contact with the skin – such as hay fever or some food allergies.

Illustration: Reaction to a prick test on light-colored skin

Intradermal test

The procedure here is similar to that of the skin prick test, but the allergen solution is injected into the skin (intradermal injection) instead. Intradermal tests can also detect weaker allergic reactions.

Because the injections make the test somewhat unpleasant and the injections can also trigger stronger allergic reactions, this test is generally only used if a skin prick test did not show enough of a response.

Skin scratch / scrape test

A skin scratch test can be used if the results of the skin prick test are not clear. This involves removing a small area of skin and then "rubbing" the allergen over the skin. That way, the substances reach deeper layers of tissue than possible in the skin prick test, with the aim of provoking a stronger reaction. The skin scrape test is similar, but only the outermost layer of skin is removed.

In these tests, it’s not possible to regulate exactly how much of the allergen enters the skin and tissue. They are also more likely to cause non-allergic skin irritation than the skin prick test is. So this test is considered to be less reliable.

Applying the allergen externally

If your doctor thinks that your skin will react very strongly, the substance can simply be rubbed onto your forearm without breaking your skin. Compared to the skin prick test, it will take a little longer for the results to appear: If you have an , a reaction will be visible after about 20 minutes. Light skin will then become red with swollen bumps (wheals). Wheals develop on dark skin, too, but the affected skin is darker in color rather than red.

Patch test

This test is used if you are thought to have an where the symptoms only become apparent one half to three days after contact with the allergen. The triggers are often single substances found in:

  • Medications such as local anesthetics (lidocaine, tetracaine)
  • Cosmetics (preservatives and fragrances, or essential oils)
  • Jewelry (nickel or cobalt)
  • Gloves or condoms (latex)

A patch containing the suspected allergens is put on your back and left on for one full day. If there is no reaction after it is taken off, your skin is checked again after another 24 hours, and sometimes again three days after removing the patch. If you have a contact allergy, your skin will react in a similar way to when it's inflamed (contact dermatitis): It will become swollen and itchy. Light-colored skin usually turns red as well. This is less common and less noticeable in dark skin. Dark skin is more likely to become thicker and rougher in the affected area. Small bumps and dark spots may develop too.

What do blood tests do?

To find out what is triggering an , a blood test may be needed too. It is considered if, for example, a skin disease may influence the results of the skin prick test, or if a skin test would cause too much of a reaction due to a known severe . Sometimes a blood test is used to confirm the results of a skin test that didn't provide clear enough results.

Blood is taken from a vein in the arm for this test. The blood is sent to a laboratory, where the number of a specific type of antibodies – the IgE antibodies – is measured. If someone has an , they may have more of these antibodies in their blood. But this test is only a sign of an , and not proof. Higher numbers of IgE antibodies can also be caused by other things, such as smoking or a parasite infection. The amount of these antibodies does not necessarily correspond to the severity of the symptoms, either.

How do provocation tests work?

Someone who has symptoms may not have a strong allergic reaction on their skin. Then a provocation test can be used to help find out what the trigger is.

To see if you have hay fever, for instance, an exact amount of the allergen thought to be triggering it – such as certain types of grass pollen – can be applied to the mucous lining of the nose. Then the doctor can observe whether and how strongly the body reacts with sneezing, a stuffy nose and watery eyes. Allergens can also be tested in a similar way on your eyes or lungs. Provocation tests are usually only done under medical supervision because they can cause very severe allergic reactions.

What basic things should you know?

The search for an trigger follows a sequence of steps: A skin test is usually done first, once you have talked with a doctor. A blood test is done instead if a skin test is too difficult or risky, or if the allergen in question isn’t available in a solution that can be used in skin tests. Provocation tests are only considered if the skin test or a blood test haven’t provided clear results.

Before you have a skin test, it is a good idea to tell the doctor if you have any medical conditions affecting your lungs or skin, or if you have any cardiovascular (heart or blood vessel) problems. It is also important to mention any medication you are taking that may affect how your skin reacts, such as the amoxicillin or penicillin, or painkillers like acetylsalicylic acid (the medication in drugs like “Aspirin”) or ibuprofen.

You should have no noticeable acute allergic symptoms right before doing a provocation test. Your doctor should be ready to respond quickly to any strong allergic reactions that may arise during skin tests, and particularly during provocation tests.

Biedermann T, Heppt W, Renz H et al. Allergologie. Berlin: Springer; 2016.

Brozek JL, Bousquet J, Agache I et al. Allergic Rhinitis and its Impact on Asthma (ARIA) guidelines – 2016 revision. J Allergy Clin Immunol 2017; 140(4): 950-958.

Burli A, Vashi NA, Li BS et al. Allergic Contact Dermatitis and Patch Testing in Skin of Color Patients. Dermatitis 2023; 34(2): 85-89.

Deutsche Gesellschaft für Allergologie und klinische Immunologie (DGAKI). Leitlinie Überempfindlichkeitsreaktionen auf Arzneimittel, Allergologische Diagnostik (S2k-Leitlinie, in Überarbeitung). AWMF-Registernr.: 061-021. 2015.

Pschyrembel Online. 2023.

Trautmann A, Kleine-Tebbe J. Allergologie in Klinik und Praxis. Stuttgart: Thieme; 2022.

IQWiG health information is written with the aim of helping people understand the advantages and disadvantages of the main treatment options and health care services.

Because IQWiG is a German institute, some of the information provided here is specific to the German health care system. The suitability of any of the described options in an individual case can be determined by talking to a doctor. informedhealth.org can provide support for talks with doctors and other medical professionals, but cannot replace them. We do not offer individual consultations.

Our information is based on the results of good-quality studies. It is written by a team of health care professionals, scientists and editors, and reviewed by external experts. You can find a detailed description of how our health information is produced and updated in our methods.

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Updated on February 1, 2024

Next planned update: 2027


Institute for Quality and Efficiency in Health Care (IQWiG, Germany)

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