Food Allergy Fact and Fiction

What Are Food Allergies and Where Do They Come From?

Just the Facts

An itchy rash. Diarrhea. Upset stomach. Is it a virus, a food allergy, or something else? Knowing the difference can help you and your baby rest, and eat, easier.

In a food allergy, the immune system reacts to a harmless food as if it were a threat and creates histamines and antibodies to fight it. Symptoms range from a tingling in the mouth and swelling of the tongue and throat to difficulty breathing, hives, vomiting, abdominal cramps, diarrhea, and a potentially fatal drop in blood pressure or shock, known as anaphylaxis. Every exposure may increase the reaction's severity. (Intolerances, also called sensitivities, may cause diarrhea, but they're not allergies; they occur when the body has trouble digesting a certain food.)

Ninety percent of all food-allergic reactions are to peanuts, eggs, milk, shellfish, wheat, soy, fish, and tree nuts (such as almonds and walnuts). Fewer than 10 percent of kids with food allergies react to corn, strawberries, and citrus fruit. Because babies don't typically eat a wide range of foods, the most common allergies seen early on are to milk, eggs, and soy, notes Dr. Sicherer.

As their immune systems mature, most children outgrow allergies to egg and milk by the time they enter elementary school. Food allergies can be triggered at any age, even after a food has been ingested for years, but allergies to peanuts and different types of fish are typically the most life-threatening and often manifest themselves early and last for life.

The Genetic Connection

As an infant, my eldest son struggled with bouts of blotchy eczema and asthma, conditions often shared by those with food allergies. "Eczema is one of the earliest markers of an allergic person," says Dr. Assa'ad. A family history of eczema, asthma, and allergies also raises the stakes. Seasonal and environmental allergies, like my hay fever and my husband's allergy to dust, directly increased our two sons' risk. And although both my boys faced and overcame an egg allergy early in their lives, their peanut allergy remains.

"You may inherit the susceptibility to become allergic. It's not anything that the mother does when she's pregnant or breastfeeding or anything that the father does," says Dr. Assa'ad. Some children just get a bigger share of the genes that predispose them to food allergies.

If your infant is diagnosed with asthma, eczema, or a food allergy, follow your doctor's instructions on the timing of solid foods, says Dr. Greer. If none of these conditions is present, then you don't have to wait to introduce any food once your infant begins solids between 4 and 6 months, he adds. (Of course, certain foods might also have to be restricted because of other health concerns or choking hazards.)