Living with a food allergy or intolerance can be a huge hassle. So it’s surprising how many people think they have sensitivities to certain foods — and alter their lives accordingly — when they really don’t.

“Research shows that as many as 20 percent of people claim to have food allergies when the number is actually around 3 to 4 percent,” says Hugh Sampson, director of the Jaffe Food Allergy Institute at the Mount Sinai Medical Center in New York. He concedes that the number of people with milder reactions — nonallergic symptoms that flare up when they eat certain foods — is higher, but he thinks the problem is still generally overestimated. That’s partly because reactions to food can change over time. And various symptoms are sometimes mistakenly attributed to food when they really stem from something else.

On the other hand, some very real and potentially life-threatening food allergies appear to be on the rise. For example, a 2010 report comparing surveys of U.S. households in 1997, 2002 and 2008 found a steady increase in allergies to peanuts and tree nuts in children. The reasons for the trend aren’t clear.

Allergy or intolerance?

Food intolerances occur in the digestive system, where, for various reasons, the body is unable to properly break down certain foods. That causes such symptoms as gas, bloating and diarrhea. Some of the more common culprits are sugars — specifically, lactose, found in dairy products, and fructose, found in fruit, honey, some vegetables and in some soft drinks and fruit drinks.

But not all intolerances cause digestive symptoms. For example, cheese, chocolate and wine can trigger migraine headaches in some people.

A food allergy is an abnormal response to food triggered by the immune system. Within minutes to hours of coming in contact with even a trace amount of something they’re allergic to, people might experience symptoms in their gastrointestinal tract (nausea, vomiting, diarrhea), on their skin (itching, swelling, hives) and in their respiratory system (congested, runny or itchy nose; sneezing, coughing or wheezing). In some cases, an allergen — most often nuts — can trigger anaphylaxis, a severe reaction that happens quickly and can include swelling of the throat, difficulty breathing, dizziness and loss of consciousness. Without immediate treatment — an injection of epinephrine (adrenaline) and medical attention — it can be fatal.

While people with an intolerance to certain foods might get gastrointestinal or other symptoms, they can still eat them without serious consequences. Intolerances and allergies also differ in the way they progress. Intolerance to certain foods, including milk, becomes more common with age. In contrast, many food allergies are outgrown by adulthood, though nut, fish and shellfish allergies tend to persist throughout life.

Diagnosing food allergies

If you suspect you have a food allergy, it’s important to see a specialist who is board-certified in allergy and immunology. And if a doctor diagnosed an allergy years ago, it makes sense to check again. Your allergy may have subsided or you may have received an incorrect diagnosis based on outdated testing methods.

Because of the shortcomings of lab tests, they shouldn’t be used alone to diagnose a food allergy, according to recommendations by the National Institute of Allergy and Infectious Diseases. Instead, a doctor should give you a physical examination and take a detailed medical history first. He or she might also ask you to record everything you eat as well as any symptoms. Identifying the culprit is made slightly easier by the fact that in the United States, 90 percent of food-allergy reactions stem from just eight items: eggs, fish, milk, peanuts, shellfish, soy, tree nuts (including almonds, cashews, pecans, pistachios and walnuts) and wheat.

The gold standard for confirming an allergy is a placebo-controlled food challenge, in which the patient receives increasing doses of the potential allergen during one test and a placebo in another. To avoid potential bias, the test is double-blind, meaning that neither the tester nor the patient will know which dose is the placebo until it’s over. Because of the risk of a severe reaction, the test should be done only in a doctor’s office.

Currently, the only treatment for food allergies is to avoid the food that causes them. People at risk of anaphylaxis should also carry at least one prescription self-injector of epinephrine (EpiPen and others). It’s also a good idea to program cellphones with an “in case of emergency” (ICE) contact and allergy information in the “notes” area.