What you've heard about food allergies may not be true

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Food Allergies Tooga/Digital Vision/Getty Images / Today

Myth: Food allergies begin in childhood

Fact: “Food allergies are often diagnosed in childhood, but they can develop at any time in a person’s life,” says KT Park, M.D., a gastroenterologist at Lucile Packard Children’s Hospital at Stanford University in Palo Alto, Calif. Although kids can outgrow some food allergies—like eggs and soy—shellfish and nut allergies last a lifetime. Food allergies that develop later in life usually don’t go away.

Myth: If a food doesn’t agree with you, you have a food allergy

Fact: "People use the word ‘allergy’ as a catch-all phrase, but technically not all reactions to food are allergies,” says Rachel Begun, R.D., spokesperson for the Academy of Nutrition and Dietetics. Only about 6 to 8 percent of kids and 3 to 4 percent of adults have true food allergies, but around 25 percent of people think they do because they've experienced discomfort—such as bloating—after eating a particular food. “A true food allergy is when the immune system believes a food to be a foreign [substance] and attacks it in an attempt to remove it from the body,” says Begun.

If you have a true allergy, the immune system reacts abnormally to a food, usually within a few minutes to hours of eating. Symptoms vary but can include itching in the mouth, hives or vomiting and abdominal cramps. Severe allergic reactions, called anaphylaxis, consist of trouble breathing, a feeling that your throat is closing or chest tightness. Anaphylaxis can be life-threatening if not treated immediately, says Dr. Park, so call 911 immediately.

Myth: A food allergy and food intolerance are the same thing

Fact: Food intolerance may occur because you lack the digestive enzyme to process a certain component of food such as the lactose in milk. Or, it may be that your body is reacting to naturally-occurring components of food, such as sulfites, or flavor-enhancers, like MSG. The symptoms of food intolerance are usually mild gastrointestinal distress—bloating or diarrhea—after eating or sensations of warmth or flushing. While the symptoms of food intolerance are uncomfortable, they’re not life-threatening, says Park.

In some cases of food intolerance, you may even be able to eat small amounts of the offending food without trouble. Or you may be able to take enzyme supplements to improve digestion, such as lactase (Lactaid) if you have lactose intolerance, for example. On the other hand, with a food allergy, you must avoid the offending food forever.

Myth: A simple allergy test can tell me if I have food allergies

Fact: Whether you have a positive skin test or a blood test that shows you’ve produced antibodies to a particular food, you still need a physical reaction to a particular food to be diagnosed with an allergy. “The only reliable diagnosis is based on a thorough, detailed history,” says John Leung, M.D., director of the Food Allergy Center at Tufts Medical Center and Floating Hospital for Children in Boston. “Lab work is [only] used to confirm the diagnosis.” Your doctor may also suggest an elimination diet—you stop eating the suspected food to see if your reactions cease, or a food challenge, during which small amounts of the suspected food are introduced into your diet and your reactions are observed under strict medical supervision.

Myth: If you think you have a food allergy, just avoid that food

Fact: If you suspect you have a food allergy, see your doctor immediately. A mild reaction once could mean a serious reaction the next time. “True food allergies are rapid in onset,” says Dr. Leung. “You can develop life-threatening anaphylaxis within minutes after eating, so you need to carry medication, such as an Epi-Pen, for severe reactions.” On the other hand, once you’re thoroughly evaluated, you may discover that what you think is an allergy really isn’t. “Often we see patients who have been avoiding foods they don’t even need to avoid,” says Leung.

Myth: Artificial flavors and additives cause most food allergies

Fact: It’s the foods themselves, rather than the additives, that cause most true food allergies. And it's eight foods that cause 90 percent of all food allergies: Milk, eggs, peanuts, tree nuts (such as walnuts), fish, shellfish, soy and wheat. “You may experience some sort of food intolerance from additives such as MSG or sulfites,” says Park “but your reaction isn’t going to manifest itself as anaphylaxis as it would with a true food allergy.”

A version of this story originally appeared on iVillage.