When Ruth Ann Guhr learned that her 2-year-old granddaughter had frequent bouts of diarrhea, she immediately thought "food allergy."

Thirty years earlier, her own son had experienced the same symptom after drinking cow’s milk. History seemed to be repeating itself.

However, with the gains in research and allergy understanding made during the past few decades, the Guhrs, of Potwin, Kan., soon discovered that their granddaughter, Ashley, was not allergic to cow’s milk. She was intolerant.

It’s a common mistake, says Dr. Jon Jones, an emergency medicine physician in Wichita, Kan.

"Lactose intolerance is not really a food allergy," Jones says. "It can be difficult for parents and grandparents to understand and to recognize the difference."

Lactose intolerance, like Ashley’s, is a common example of food intolerance caused by lacking an enzyme needed to digest milk sugar. When the child eats milk products, symptoms such as gas, bloating, abdominal pain and diarrhea can occur.

A food allergy, however, occurs when the immune system reacts to a certain food. The result can be hives, asthma or other more serious allergic reactions.

Jones says the immune system mistakenly believes certain foods to be harmful. In its effort to protect the body, the immune system creates antibodies. When a child eats certain foods, the immune system releases massive amounts of chemicals and histamines to protect the body, triggering allergic reactions that can affect the skin, gastrointestinal tract and respiratory and cardiovascular systems.

The majority of the toddlers Jones cares for in the emergency room have allergic reactions ranging from vomiting to a skin rash covering the entire body.

"The allergic reactions usually occur within a couple of hours of eating the offending food and can be of the nuisance variety -- fussiness and discomfort -- to severe," he says.

However, finding the offending food supply isn’t as difficult as once thought, says Jones, because only eight foods account for 90 percent of allergic reactions.

He has found that most of his patients have had reactions to peanuts, followed by other types of nuts, like walnuts and pecans. Others have been allergic to fish, shellfish, eggs, milk, soy and wheat.

To make his diagnosis for any of the hundreds of his young emergency room patients with suspected food allergies, Jones helps parents recall the child’s eating habits and diet.

"I ask them if there have been any new foods eaten recently," he says. "That can be one of the best ways of figuring out what is causing the problem."

If the source of the allergic reaction cannot be determined, Jones often advises parents to take their toddler to an allergist for specialized testing. An allergy evaluation can include a physical exam, medical history and a series of allergy tests. Parents often are asked to keep a detailed list of what their child eats, or even to have them stop eating certain foods.

Once parents know the exact ingredient to be avoided, they should continue to ask questions of their child’s physician. It is possible for a child to be allergic to peanuts, for example, but not to a food containing peanut oil.

The biggest culprit for food allergies in toddlers appears to be peanuts. Once considered a life-long allergy, a recent study published in the Journal of Allergy and Clinical Immunology found that the majority of toddlers with peanut allergies outgrew them. Of those who didn’t, the severity of reaction dramatically decreased with age.

By the time a toddler reaches school age, food allergies have usually presented themselves. However, it can be important to remember that allergic reactions to foods served in a school setting are possible. According to the American Academy of Allergy, Asthma and Immunology (AAAAI), about 25 percent of reactions in school-age children occurred at school, either in cafeterias, playgrounds or classrooms.

The Food Allergy Network in Fairfax, Va., estimates as many as 200 people die each year from food allergy-related reactions.Contrary to popular belief, toddlers are not at greatest risk. Teenagers, it seems, account for the majority of severe and often fatal, food allergy reactions.

The best treatment for food allergies, Jones says, is one of self-awareness and common sense.

"Avoidance of the food you are allergic to is the best prevention," Jones says. "Read food labels."

For other parents and grandparents a food intolerance can mean years of careful grocery shopping and food preparation. To ensure a lactose intolerant toddler still receives many of the nutrients contained in milk products, a diet rich in dark green, yellow and red vegetables, as well as tofu, fortified juices and meat, can do the trick.

For the Guhrs, having a lactose intolerant toddler meant learning to substitute water or apple juice in a pancake or cookie recipe that called for milk and experimenting with rice milk and other "lactose-free" items, before striking the right balance.

About the author: Laurie Dove is an iParenting contributing writer. She lives in Newton, Kan. with her husband and two children.