Food Allergy or Food Intolerance? Here’s How to Tell the Difference

Do you get diarrhea every time you drink milk? Bloat every time you eat bread? Feel tingly and itchy any time you have peanut butter? You may assume that you have an intolerance to that food or are perhaps allergic to it. But despite all the attention surrounding food intolerances and allergies, the answer isn’t so clear cut.

What is a food allergy?

True food allergies are when the immune system becomes sensitized and overreacts to a particular component of a food, says David Stukus, MD, allergist, director of the Food Allergy Treatment Center at Nationwide Children’s Hospital in Columbus, Ohio, and a member of the American College of Allergy, Asthma, and Immunology (ACAAI). This extreme immune response can be triggered by eating even a small amount of the food and leads to symptoms including hives, digestive issues, swollen airways, and in some cases, death through anaphylactic shock, he says.

Food-related anaphylaxis is a life-threatening whole-body response to an allergen that kills about two adults each day in the U.S. Symptoms of anaphylaxis include difficulty breathing, swelling in the throat, a sudden drop in blood pressure, pale skin or blue lips, fainting, and dizziness, according to the ACAAAI.

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What is a food intolerance?

In recent years, doctors are seeing an increase in complaints of food intolerances, where people feel ill after eating certain foods but the symptoms don’t rise to the level of an allergy or are different altogether. “These people can have some of the same symptoms of a food allergy but may have additional symptoms and usually don’t show any of the physiologic changes associated with a food allergy,” says Rabia De Latour, MD, a gastroenterologist and assistant professor at the NYU School of Medicine.

Rather than being the result of an overactive immune response, food intolerances are thought to be the result of an inability to digest a certain food. They are not deadly, cannot cause anaphylaxis, and can vary widely in severity, Dr. De Latour says. Signs of a food intolerance can include those of a food allergy and/or other symptoms like brain fog, hyperactivity, depression, stomach pain, irritable bowel syndrome, bloating, acne, hair loss, weight gain or loss, exhaustion, and anxiety.

Gluten intolerance is the most widely reported food intolerance but dairy, eggs, soy, sugar, meat, and nuts are other common offenders.

Are food intolerances even real?

Food allergies are relatively simple to diagnose and treat. Food intolerances, on the other hand, generally aren’t recognized as an official medical diagnosis, are much harder to define, have a wide variety of symptoms, exist on a spectrum, may have a psychological component, and have many potential treatments beyond avoiding the allergen, Dr. De Latour says.

This problem is compounded by the immense amount of bad information about food allergies, intolerances, and sensitivities on the Internet, which is often the first place people go for information, says Dr. Stukus. “People will spend hundreds of dollars for some at-home test or consultation only to be sent a long list of foods they are reportedly ‘sensitive’ to, and they’re told to avoid the foods,” he explains. “But the results are meaningless and may lead to malnutrition or other health problems.”

This nebulousness, and the fact that food intolerances seem to run in trends, can lead some doctors to write them off completely but this is a mistake, Dr. De Latour says. “Food intolerance is not well understood in the medical community but it shouldn’t be dismissed as psychological or just a fad,” she says. “People are clearly suffering even if their tests don’t show a clear pathology.”

Are your symptoms are the result of a food allergy or an intolerance?

Finding the answer to this question can be complicated and confusing for both doctors and patients, Dr. De Latour says. “You can test for allergies but a food intolerance is a diagnosis of exclusion, meaning you just have to rule out every other possibility,” she explains. “It can be incredibly frustrating not to have a clear answer but it is important to go through the process. Either way, your doctor should be able to help you find relief.”

(These are the 9 most common food allergies you should know about.)

See the right doctor

Don’t rely on a self-diagnosis, Dr. Stukus says. “There is so much misinformation and it has a negative impact on people’s medical decisions,” he says. “Make an appointment with an allergist. They have accurate tests to help you get the right diagnosis and are able to help you find a good treatment plan.” When you schedule the appointment, ask for extra time for questions and then come to your appointment prepared with a list of your symptoms and a list of questions you have, including things you may have read on the internet, he says.

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Skin tests

An allergist can diagnose true food allergies and sensitivities. They may use a “scratch” test where they draw a grid on your back and put some of each possible allergen on the skin, each in its own square, to see if it causes a reaction. “A positive result—a red, raised area called a wheal— means you reacted to a substance in a potentially allergic way. Such a positive result means the symptoms you are having are likely due to exposure to that substance,” says Morton Tavel, MD, internist, clinical professor emeritus of medicine, Indiana University School of Medicine, and author of Health Tips, Myths and Tricks: A Physician’s Advice. “In general, the stronger the response, the greater the chance of allergy to that given substance.”

It is possible to get a false positive or false negative on an allergy skin test and they are most reliable for diagnosing allergies to airborne substances, such as pollen, pet dander, and dust mites, he explains. “Skin testing may help diagnose food allergies but because food allergies can be complex, you may need additional tests or procedures,” he says.

Blood tests

There are blood tests to check for antibodies which may indicate an allergy but these have high rates of false positives, Dr. Tavel says. “The most common test, allergen-specific serum testing (for IgE antibody), is most useful for ruling out a food allergy,” he adds. There are several other types of blood tests that your doctor may order based on your individual situation, he says.

Exclusionary tests

There are no tests for food intolerances. Instead, a food intolerance is a diagnosis of exclusion. After ruling out an allergy, your doctor may test you for illnesses that can cause similar symptoms, like thyroid disease or autoimmune illnesses like celiac disease, rheumatoid arthritis, or lupus, Dr. De Latour says. Your doctor also may order a blood panel to look at your overall health.

Elimination tests

One of the simplest things you can do to see if you have a food intolerance is to completely eliminate the food from your diet for a minimum of one month and see if your symptoms improve, Dr. De Latour says. This is simple but it isn’t necessarily easy—you have to read every label and be extra careful when dining out. For people who suspect multiple food intolerances you can try an elimination diet, which removes the most common culprits, she says, adding these are best done under the supervision of a doctor.

Consider other factors

If you’ve tried all of these tests and are still unsure of what is causing your symptoms, it may be time to consider other non-medical possibilities, Dr. De Latour says. The brain and the body are very connected so things like depression and anxiety can have physical manifestations that mimic food intolerances, like gastrointestinal problems, headaches, fatigue, and brain fog, she says. Food aversions can also cause strong physical reactions.

Next up: 9 common foods that are responsible for almost all food allergies.