Food allergies occur when the body’s immune system reacts to a protein in a specific food. When exposed to the food, the body produces antibodies to the protein. Once enough antibodies build up, an exposure to the food will trigger allergic symptoms.

A food intolerance is an abnormal reaction to a food. With a food intolerance, a person usually does not make enough of a certain enzyme needed to digest some part of a food.

Diarrhea and vomiting are the most common symptoms. Skin rashes, itching, runny nose, wheezing, tightness in the throat, and swelling of the lips, tongue, or mouth may also occur.

Symptoms may appear within a few minutes or take as long as 48 hours to appear.

As a general rule, if symptoms are triggered by an allergy, your child won’t have a fever.

The food allergies most common among young children are those to cow’s milk, soy, egg whites, wheat, and citrus. (For detailed information specifically about cow’s milk allergies, see Cow’s Milk Allergy.) Any food has the potential to trigger an allergy, though.

Lactose intolerance and gluten intolerance are two of the most common types of food intolerances. (For detailed information specifically about lactose intolerance, see Lactose Intolerance.) Children can also have an intolerance to food additives, such as monosodium glutamate, nitrates, nitrites, sulfites, and dyes.

True food allergies are quite rare. No more than 2 in 100 children have a true food allergy. However, about one-third of children may have an adverse reaction to a food, which may be mistaken for a food allergy.

With a food allergy, the body’s immune system mistakenly tries to defend against certain food proteins as if they were invading germs.

With an adverse reaction to a food, although symptoms may be similar to those of an allergy, the immune system is not involved.

In either case, it is usually recommended that the problem food be eliminated from the diet.

Allergic reactions can be serious. Seek medical assistance immediately if your child

• Has trouble breathing or turns blue.
• Has generalized hives (smooth red swellings that itch, burn, or sting).
• Develops swelling in the head and neck.
• Has bloody diarrhea.
• Is extremely pale or weak.

Even if your child does not show any of these severe symptoms, you should consult your health care professional soon if you suspect that your child has an allergy.

Generally, the suspect food is eliminated from the diet for 2 weeks to see if symptoms lessen.

If the cause of symptoms is not clear, skin or blood tests may be performed.

If a parent or sibling is allergic to a food, your child may be more likely to develop an allergy. However, you may increase the chances of preventing a food allergy if you eliminate the offending food from your toddler’s diet.

Delaying the introduction of highly allergenic foods may help. If a child has a family history of allergies, it is best not to introduce cow’s milk, soy, wheat, corn, and citrus until after the first birthday. High-risk children also should not eat eggs before their second birthday or peanuts and fish before their third birthday.

The only way to treat a food allergy is to avoid the troublesome food.

To do so completely, parents must carefully read the labels of processed foods for ingredients that are variations of the offending food.

It depends. About half of all children who develop a food allergy before age 3 eventually outgrow it, usually by about age 7 years.

Children who develop an allergy after age 3 years are less likely to outgrow it.

Allergies to nuts and shellfish are more likely to persist for life. Also, intolerances such as wheat sensitivity in celiac disease are lifelong conditions.

If you want to test, a food challenge should only be performed under your doctor’s supervision in his office. Never attempt a food challenge yourself at home.