There are several ways to test for food allergies. Doctors often use a combination of these methods to ensure an accurate diagnosis.
Allergies occur when your immune system overreacts to something in the environment, such as pollen, mold, or certain foods. The Centers for Disease Control and Prevention (CDC) estimates about 4 to 6 percent of children in the United States have food allergies. Adults can also have them.
While countless foods can cause allergic reactions in some people, the CDC notes just eight foods are responsible for 90 percent of serious allergic reactions in the United States.
- cow’s milk
- tree nuts, such as walnuts, almonds, Brazil nuts, and cashews
Symptoms of a food allergy may start shortly after ingesting the food, or they may be delayed for a few hours. Common symptoms of a food allergy include:
- swelling of the tongue, mouth, or face
- red, itchy bumps on the skin (hives)
- itching of the lips and mouth
- stomach pain
- nausea, vomiting, or both
- a life-threatening reaction known as anaphylaxis
If you or your child have symptoms of a food allergy, consider looking into food allergy testing. Read on to learn about the different testing methods, including those you can do at home.
You can find kits that claim to test for food allergies both online and in drugstores. But while these kits offer convenience, they aren’t very reliable on their own. They may also seem less expensive than a doctor’s visit, but keep in mind that most insurance plans don’t cover home testing kits.
Most kits have you prick your finger and send a blood sample off to a laboratory. Other kits require sending in a sample of your hair. After analyzing your sample, the company will give you your test results.
Food allergy testing generally relies on seeing if your blood produces immunoglobulin E (IgE) antibodies in response to certain foods. But some home tests only measure immunoglobulin G (IgG) antibodies. There’s no evidence that this can help diagnose a food allergy. In addition, hair samples don’t contain IgE.
Keep in mind that food allergies can be serious. It’s best to make sure you get an accurate diagnosis from a doctor to avoid potentially life-threatening reactions.
After taking a detailed personal and family history, doctors typically use a skin prick test first when trying to diagnose a food allergy.
It involves placing a small amount of liquid extracts of certain foods on your skin, usually on your back or arm. Next, they’ll use a small tool to lightly prick your skin, allowing some of the extract to get below your skin’s surface.
They may also include nonfood allergens, such as pollen. This is because people allergic to pollen can also experience an itchy mouth and throat after eating certain fruits and vegetables, such as apples or kiwis.
The reaction occurs because the proteins found in these foods are similar to those found in pollen, which can confuse the immune system. Allergists refer to this as oral allergy syndrome or pollen fruit syndrome.
After 15 to 20 minutes, they’ll examine the area for any signs of an allergic reaction, such as bumps or a rash.
While skin prick tests are more reliable than home testing kits, they can still produce false positives. This means the test shows you may be allergic to something, even though you don’t have any allergy symptoms when exposed to the substance. Still, it provides useful information that can help you and your doctor decide what to do next.
In other cases, your healthcare provider might do a blood test, especially if you use medications that could interfere with the results of a skin prick test. They might also do this if you use medications that could interfere with the results of a skin prick test.
To do a blood test, your doctor will take a small sample of blood and send it to a laboratory. Next, the sample will be exposed to different foods. If it releases a lot of IgE antibodies in response to a particular food and you have symptoms when you eat that food, you’re likely allergic to it.
It takes several days to get these results. The test is usually more expensive than a skin prick test, though many health insurance plans will usually cover it. Blood tests are also a safer option if your doctor thinks you have a higher chance of having a severe reaction to something.
Still, as with skin prick tests, blood tests can produce false positives. You may need to follow up with an additional test in the weeks or months after the initial one.
If skin pricks and blood tests don’t produce clear results, your doctor may have you come in for an oral food challenge. This is generally done in their office under close supervision, as it can sometimes cause a severe allergic reaction.
During an oral food challenge, you’ll be given a small amount of food while your doctor checks for signs of a reaction. If you don’t have a reaction, they’ll gradually increase the amount of food. If you don’t have a reaction to this larger amount, you can likely rule out a food allergy.
An oral food challenge is considered to be the most reliable and definitive food allergy test because it provides quick results that are easy to identify. This test is also helpful for adults looking to find out if they still have a food allergy from their childhood. Allergies to milk, eggs, wheat, and soy, for example, often resolve with age.
Elimination diets are sometimes used to help pinpoint specific foods that might be causing symptoms of an allergic reaction. They can also help confirm the results of skin prick or blood tests.
On their own, though, they can’t be used to distinguish between a true food allergy and an intolerance, which is less severe.
During an elimination diet, you’ll avoid eating certain foods for several weeks. Then, you’ll slowly add them back in one at a time. Each time you reintroduce a food, you’ll check for symptoms of an allergic reaction, such as:
- a rash
- a runny nose
It’s best to keep detailed notes in a journal about what you eat each day and any symptoms you have. If you don’t have any reaction to the reintroduced food, you can assume you aren’t allergic or sensitive to it and move on to reintroducing the next food.
If you want to do an elimination diet, it’s important to do it with the help of a doctor to avoid nutrient deficiencies, which can cause their own set of symptoms.
If your doctor has recommended eliminating a food due to a possible allergy, don’t start eating it again without their permission. You risk a dangerous allergic reaction.
Food allergies can cause potentially serious reactions, so it’s important to get properly tested if you think you might have a food allergy. While home test kits offer tempting convenience, they aren’t very reliable. Work with a doctor to help confirm whether you have a food allergy. They can also help rule out other causes of your symptoms, such as a food intolerance, which is different from an allergy.