Food Allergies: A-to-Z Guide from Diagnosis to Treatment to Prevention

Food allergies are real and they are common – affecting about 1 in 18 children before the 3rd birthday, and 1 in 12.5 children overall. Learn more here.

Many parents of infants and toddlers are told that food allergies don’t happen that young, or that they are very rare. We’ve learned that food allergies certainly do happen and that they are common – affecting about 1 in 18 children before the 3rd birthday, and 1 in 12.5 children overall (Pediatrics; 2011: 128 (1):e8-17).

What are they?

Food allergy is the name given to a variety of situations in which specific foods provoke some type of over-zealous immune response, which produces symptoms.

 Because the developing immune system is quite complex and has mechanisms to protect us from what we swallow, food allergies are also complex, and can result from a variety of different mechanisms and cause a variety of symptoms.

Celiac disease is an immune response to gluten – proteins found in wheat and other grains.

Lactose intolerance is not a food allergy. A missing enzyme makes milk difficult to digest, creating gas and loose stools. And the flushed cheeks that some children get when eating citrus or tomatoes are not usually an allergy.

Who gets them?

Food allergies are common, especially in the first 3 years of life. They are more common in those with a family history of food allergies, or in those with a broader allergic family history (allergy, eczema, or asthma).

Food allergies are also more common in babies who are exposed to allergic foods at an early age. About 90 percent of food allergies in babies and children are to one of 5 foods: cow’s milk, soy, eggs, peanuts, or wheat.

Most children with food allergies have an allergy to only one food, although multiple allergies are possible. A sizeable minority of those allergic to cow’s milk are also allergic to soy.

What are the symptoms?

Food allergy can be so severe that the most trivial contact with the food causes immediate itching, tingling, and/or swelling of the lips, tongue, and throat.

A food allergy can trigger full-blown anaphylactic shock. Most life-threatening food allergies are to peanuts, nuts, shellfish, or fish.

Usually the symptoms of food allergy are much more mild. Still, babies with food allergies may well be fussier than their peers. Colic can be caused by food allergies (either to the formula or to a food in the mother’s diet).

Gastrointestinal symptoms are often the easiest to recognize. A food allergy might cause loose stools, excess gas, diarrhea, nausea, or vomiting. Infants will sometimes have streaks of blood or mucus in the stools, especially with allergies to cow’s milk. Sometimes the amount of blood is too small to see, but still enough to cause anemia. Sometimes food allergies cause constipation.

Symptoms elsewhere in the body are also common. These include hives, ear infections, stuffy noses, runny noses, watery or red eyes, wheezing, asthma flare-ups, and eczema. Sometimes eczema (or fussiness) is the only sign of a food allergy, and the eczema (or fussiness) will disappear if the offending food is eliminated.

Are food allergies contagious?

Food allergies are not traditionally contagious.

How long do food allergies last?

Most young children outgrow their food allergies. Outgrowing milk and soy allergies is common by the 1st birthday. The great majority have outgrown them by the time they are 3. Even those who still have food allergies at 3 will often outgrow them, especially if they are not exposed to the offending foods for a year or two.

Some food allergies, however, are lifelong. Allergies to peanuts, nuts, shellfish, and fish are classic examples.

How are food allergies diagnosed?

Food allergies might be diagnosed when eliminating a food improves symptoms and reintroducing the food causes the symptoms to recur.

Allergy testing can also be helpful. Skin testing and RAST testing can both be used to detect food allergies. In babies, a positive result is usually a sign of a real allergy, but a negative result doesn’t give much information either way.

In preschool kids, the opposite is true. A negative result is a good indication that a child is not allergic to the food. A positive result, however, may or may not represent an allergy.

Also, many people think that having been allergy tested once tells the whole story. Allergy testing is a snapshot in time. Allergies themselves are a moving picture. Repeat allergy testing is very helpful.

How are food allergies treated?

Eliminating the offending food is the core of treatment. This can be difficult because some foods occur as hidden ingredients in many other foods. Usually symptoms will improve greatly within 3 days of eliminating the food that causes them.

Breastfeeding is wonderful for babies with food allergies. Sometimes, however, offending foods are best removed from the mother’s diet. When a baby with a cow’s milk protein allergy is fed formula, it often needs to be a protein hydrolysate formula. Lactose-free formulas and partial hydrolysate formulas do not help with real milk allergies.

If food allergies cause wheezing or other respiratory symptoms, an allergist should be involved in the care. If necessary, parents should have access to emergency medications.

How can food allergies be prevented?

Breastfeeding can prevent many food allergies. It was previously thought that this was especially true if the mother forgoes some of the most allergic foods (especially peanuts and perhaps milk or eggs). However, the evidence is not conclusive, so the American Academy of Pediatrics no longer recommends avoiding allergic foods during breastfeeding unless a baby has been diagnosed with a specific food allergy (Pediatrics 2008;121;183).

On a positive note, mothers who eat beneficial bacteria, as in yogurt, while pregnant and nursing may help prevent food allergies.

Delaying the introduction of solid foods until four to six months of age may prevent some allergies (Pediatrics 2013;132;e1529-1558).

Food hypersensitivity, Oral allergy syndrome, Allergic proctocolitis

Last medical review on: January 03, 2014
About the Author
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Dr. Greene is a practicing physician, author, national and international TEDx speaker, and global health advocate. He is a graduate of Princeton University and University of California San Francisco.
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