Think You Have a Food Allergy? Here’s What You Need to Know About Testing

Have you ever experienced tingly lips or an itchy rash without really knowing what was causing it? Or maybe you have visited the emergency room because of a scary allergic reaction. In either case, you probably wondered about a possible food allergy. And because there are many potential food allergens, it can be hard to figure out how your body responds to certain foods. 

It may be surprising to learn that there’s not a straightforward test to diagnose a food allergy. Sometimes it can be tricky even for the experts. We’ll walk you through the steps of food allergy testing so you’ll know what to expect. 

Do you need a food allergy test?

Even before you sign on for formal testing, there are a few ways to help find out if you have a food allergy, and what might be causing it. Food allergy testing can be time consuming and expensive, so you and your provider can work together to decide if you even need it.

Start a food and symptom diary 

Think of a potential food allergy as an unsolved mystery. You and your provider are the detectives trying to solve the case. Start tracking what foods you eat and the symptoms you experience. Many times this uncovers helpful clues to help you discover what’s going on.

Your provider will ask you many detailed questions about your symptoms. It can be helpful to think about these things before your appointment. Questions may include:

• What symptoms are you experiencing?

• When are you experiencing these symptoms? How soon do they happen after eating?

• Does it happen each and every time you eat a certain food?

• What treatment have you tried for your symptoms? What has helped?

Start with your regular provider

It can be tempting for some people to skip the primary care office and go straight to an allergist. But your regular provider is the best place to start.

At your appointment, they will analyze your symptoms and thoroughly examine you. They may find clues that something other than a food allergy is causing your symptoms. And if the clues point toward a food allergy, they can provide the referral to the right specialist. 

Types of allergy testing 

After a thorough history and exam, your prover or allergist may decide you need more testing. Depending on your symptoms, there are two types of testing your provider may use:

1. Combination of a blood test and skin prick test

2. Food challenge

Sometimes they’ll need the results of both tests to find the cause of your allergy.

Blood test

When your body detects substances that may be harmful, it makes immunoglobulins — a type of protein. Most of the time, these immunoglobulins fight bacteria and viruses, but allergens can also trigger this process.

Your body makes a specific immunoglobulin E (IgE) for each thing it identifies as an invader. So a blood test for allergies measures the level of IgE for each potential allergen. When these IgE levels are above a certain number, they suggest you have an allergy to that food.

There are IgE blood tests for the foods that most commonly cause allergies, including:

• Dairy

• Eggs

• Nuts and seeds (peanuts, almonds, cashews, hazelnuts, pecans, pistachios, walnuts)

• Sesame

• Meats

• Seafood

• Beans

• Grains

• Fruits

• Vegetables

Blood tests are about 95% accurate in diagnosing food allergies. This means that if you have a positive blood test, there’s a 95% chance you have a true allergy.

Usually you do these blood tests at a laboratory. But sometimes you can do them at your allergist’s office. Depending on the number of allergens you’re testing for, your provider may draw one or several tubes of blood. It usually takes 1 to 2 days to get the results.  

Skin prick test

Your healthcare team might recommend a skin prick test alongside blood tests. You do these tests in an allergist’s office. Here’s what to expect:

• About 1 week before your test, you may have to stop taking your normal medications — like antihistamines and acid blockers. These medications can interfere with test results. Your allergist’s office will give you a list of medications to avoid prior to the testing. 

• Allergists usually perform the test on the skin of your back or arm. They’ll mark your skin with a marker — each mark corresponds to a different allergen.

• The allergist uses a  small device to place food extracts at each mark. This device makes a superficial scratch at each mark on the outermost layer of skin. This part may be slightly uncomfortable, but it should not hurt or bleed. 

• After the scratches, the allergist will come in at intervals to check your skin and see how it’s reacting. These spots can become very itchy, but it's best not to touch them. This can alter the results of your testing.

The most common food allergens have standardized extracts for skin prick testing. These are like the blood tests listed above.

Unlike blood tests, a positive skin test result is a little less reliable — it does not always mean you have an allergy. As many as 60% of positive tests do not actually correspond to a true allergy. This is why experts often pair skin tests with blood tests. The skin test alone can’t diagnose a food allergy.

A negative skin test is actually more useful. If your skin test is negative, that means you’re definitely not allergic to that food. 

Food challenge

The best test for food allergies is the food challenge. In this test you avoid whatever food you think might be causing the allergy for 1 to 2 weeks. Then — at an appointment with an allergist — you see how your body reacts when you eat it.

To do this, an allergist gives you increasing amounts of the food. And they monitor you for signs of a reaction after each amount.

This approach is the most reliable way to know for sure if you have a food allergy. But it’s also risky. You can have a serious allergic reaction — even anaphylaxis — when you eat the food. So a food challenge is not always the best approach for everybody. And you should only do a food challenge with a trained professional.

What about at-home allergy tests?

There are several at-home allergy tests for food allergies and sensitivities. But experts do not recommend them. There’s little evidence to support their use, and there’s a good chance they can give you inaccurate results. 

Why trust our experts?

Written by:

Jill L. Jaimes, MD

Jill L. Jaimes, MD, is a board-certified pediatric emergency medicine physician with over 20 years of clinical experience. She received her medical degree from Baylor College of Medicine and completed her residency and fellowship training at Texas Children’s Hospital.

Edited by:

Katie E. Golden, MD

Katie E. Golden, MD, is a board-certified emergency medicine physician and a medical editor at GoodRx.

Our editorial standards

Meet our experts