Allergy or Intolerance: How Can You Tell the Difference?


If you’ve had a reaction — upset stomach or diarrhea, for example — to a certain food, you may think you have an allergy. But it’s more than likely to be a food intolerance.

When you have an allergy, symptoms are likely much more severe and sometimes life-threatening, depending on the cause.

The key is to understand the differences between an intolerance and an allergy. That way, you’re better prepared to handle them.

“While symptoms of allergy and intolerance may appear similar, one clear difference is how they affect your body,” says allergist/immunologist Mark Aronica, MD. “An allergy is mediated by the immune system and can affect multiple organs. However, digestive issues usually point to a food intolerance, not an allergy.”

Signs of intolerance

You may hear people say a certain food “doesn’t agree” with them. So what does that mean? What types of things show up as an intolerance for some people? Dr. Aronica lists these common culprits:

Allergic reactions are different

Allergy symptoms, on the other hand, are much more intense. And they may occur within 30 minutes or up to two hours later.

If you have an allergy to peanuts or soy, for instance, you may have a rapid, severe reaction — called anaphylaxis — to even a small amount. This can include a rash or hives; swelling of the lips, tongue or throat; and difficulty breathing or wheezing.

“If not treated immediately with an epinephrine or adrenaline injection, this type of reaction is sometimes fatal,” Dr. Aronica says.

Other things that commonly cause an allergic reaction include:

The family connection

“A common question I hear from patients is whether an allergy is hereditary or developed over time,” Dr. Aronica says. “The short answer is both.”

There is a higher risk of environmental allergies and asthma in children if one or both parents also are allergic.

Allergies typically become apparent early in childhood, especially from foods like milk, nuts, eggs and soy. But sometimes food and other allergies can develop later in life, he says.

Recent research suggests that the introduction of potentially allergenic foods like peanut early in life may help prevent the development of peanut allergies in high-risk infants.  If you are concerned, speak with your allergist.

An intolerance is sometimes genetic, but can develop over time.

One common example is lactose intolerance: As you age, your body may produce less of the enzyme that helps digest lactose in dairy products, Dr. Aronica says.

Diagnosing allergies and intolerance

Your medical care provider can help you find out whether you have an allergy or intolerance. He or she will help establish a plan to help control your symptoms.

Allergy skin-testing can identify your body’s reaction to allergens. A blood test can pinpoint elevated levels of allergy antibodies that your immune system produces.

Determining the cause of a food intolerance is not an exact science, however, Dr. Aronica says. In some cases, you may lack the enzymes you need to digest proteins in food.

It may help to keep a food diary to record what you eat, when you have symptoms and what they are. If you notice that a food or ingredient consistently gives you discomfort, it’s likely an intolerance.

Managing your reactions

“Avoidance is the best prevention method for keeping most allergies and intolerances in check,” Dr. Aronica says. In other words, steer clear of the substances that bother you.

Medication may help with more subtle cases of intolerance. For lactose intolerance, for instance, over-the-counter medications may help you enjoy dairy foods like milk, cheese and ice cream, he says.

Antihistamines like eye drops, nasal sprays and pills can help stop the sneezing, itchy eyes and runny nose that environmental allergies may cause.

But if you know you have an allergy to a specific food or to insect venom, carry an epinephrine auto-injector such as AUVI-Q® or EpiPen® with you at all times, Dr. Aronica says. Discuss any drug allergies with your doctor.