What allergies are there—and why you shouldn’t take medication before the test

Do you suffer from a rash, itching, or watery eyes and suspect an allergy? Then an allergy test is the right way to get clarity. But many people don’t know this: If you have previously taken antihistamines, the test may be inaccurate under certain circumstances. In this article, we explain why this is the case, how to prepare optimally, and what to do in the event of an allergic reaction.

What allergies are there?

Allergies are widespread—but they often manifest in very different ways. Some people react to pollen with sneezing and watery eyes, while others develop an allergic rash after eating certain foods. For others, animal dander or house dust causes breathing difficulties. Insect venom, medications, or contact substances such as nickel can also cause allergies. Symptoms range from mild discomfort to severe, life-threatening reactions.

Why is an allergy test important?

An allergy test helps you find out which substances irritate your body. Only when you know what you are allergic to can you specifically avoid triggers, take preventive measures, or start suitable treatment. There are various testing methods—from the classic skin test to the modern blood test—but good preparation is crucial for all of them.

How do antihistamines work—and why can they affect the test?

Antihistamines are medications that many allergy sufferers take in everyday life. They block the effects of histamine, a substance produced by the body and released during allergic reactions. However, this very effect—such as redness, swelling, or itching—is deliberately triggered during an allergy test to make a reaction visible.

So if you have taken antihistamines shortly before the test, your body may not react or react only minimally—even if an allergy is present. This means: The test shows a negative result even though you are actually allergic.

Not all tests are equally susceptible to inaccurate results:

Test type	Effect of antihistamines
Prick test (skin test)	❗️ Yes, significantly affected
Blood test (e.g., IgE test)	✅ Little to not at all affected
Patch test	⚠️ Possible, but less relevant

How long should you stop taking antihistamines before an allergy test?

To ensure that the test can be evaluated reliably, you should pause antihistamines a few days before the test. The exact duration depends on the active ingredient. As a general rule, for common medications such as cetirizine or loratadine, an interval of 3 to 5 days is sufficient. For long-acting medications such as desloratadine or fexofenadine, you should stop taking them 7 days beforehand.

If you are unsure, be sure to speak with your doctor or the practice conducting the test. Other medications—such as cortisone-containing creams or tablets—can also affect the results and should be discussed with a doctor beforehand.

What to do in the event of an allergic reaction?

If you experience an acute allergic reaction regardless of the test, it is important to act quickly. Early signs may include itching, skin redness, hives, shortness of breath, or circulatory problems. In such cases:

If possible, remove the trigger (e.g., a food or contact substance)
Sit down calmly and remain relaxed
Take an antihistamine (if prescribed)
In the event of severe reactions or shortness of breath: call emergency services (112) immediately

People with known severe allergies are advised to carry an allergy emergency kit with an epinephrine pen.

Conclusion: Good preparation leads to clear results

If you want to know which allergies you really have, an allergy test is a useful measure. However, to ensure that the test is meaningful, you should avoid taking antihistamines beforehand—and ideally seek advice from a doctor or pharmacist.

MYBODY® helps you understand your body better

At MYBODY®, we offer modern health analyses and self-tests for home use—for example, for detecting food intolerances, analyzing the microbiome, or checking your nutrient status.

👉 Find out more: www.mybody-x.com