According to Food Allergy Research and Education, a nonprofit supporting individuals with food allergies, about four percent of adults and about eight percent of children have a food allergy. Interestingly, about 20 percent of adults believe they have a food allergy. Clearly, there is confusion between a true food allergy and food intolerance.

Food allergies are common in the United States. According to Food Allergy Research and Education, a nonprofit supporting individuals with food allergies, about four percent of adults and about eight percent of children have a food allergy. Interestingly, about 20 percent of adults believe they have a food allergy. Clearly, there is confusion between a true food allergy and food intolerance.

A food allergy is an immune system response. It happens when the body mistakes a food as harmful and mounts a defense. Usually the problem is a specific protein in the food. Antibodies battle the invading food protein, creating the allergic response. The reaction can range from mild, such as a rash or hives, to severe, as in life-threatening breathing difficulties.

Even a tiny amount of an offending food can trigger an allergy, and the allergic response occurs every time the food is eaten. This is a life-altering condition and requires the complete removal of that food from the diet.

Eight foods account for the about 90 percent of food allergens: cow’s milk, eggs, peanuts, tree nuts, soy, wheat, fish and shellfish. These ingredients must be listed on all food labels if they are present in any amount.

Food allergies can strike children or adults at any time. Reactions may become more severe with time, or the allergy can get better. Many children outgrow food allergies, especially those to milk or eggs. Food allergies are typically more common in people who have other family members with allergies.

The first time you eat a food to which you are allergic, your immune system responds by creating a specific antibody. When you eat it again, it triggers the release of the antibody and other chemicals, including histamine, in an effort to expel the invader. Histamine is a powerful chemical that affects the respiratory system, gastrointestinal tract, skin and cardiovascular system. Symptoms usually occur within minutes.

Proper diagnosis of a food allergy is important so that you can 1) avoid the food that triggers a reaction and 2) be prepared by carrying epinephrine to counter any accidental exposure to the allergen. Being allergic to a food also can result in being allergic to a similar protein in a different food. This is called cross-reactivity.

For example, a person allergic to cow’s milk may also react to milk from another mammal, such as goat milk.

Unlike an allergy, a food intolerance is a digestive system response, not an immune system response. It occurs when something in food irritates a person’s digestive system or when a person is unable to properly digest or break down the food. Intolerance to lactose, which is found in dairy, is the most common food intolerance.

Food intolerances are sometimes dose-related, so you may not have symptoms unless you eat a large portion of the offending food or eat it frequently. Symptoms of food intolerance include nausea, stomach pain, gas, cramps, bloating, vomiting, heartburn, diarrhea or headache.

Food intolerances can be caused by many factors. In some cases, as with lactose intolerance, the person lacks the enzymes necessary to properly digest the food. Also common are intolerances or sensitivity to some chemical additives, such as various dyes, sulfites or flavor enhancers. Some people have difficulties with gluten, a protein in wheat. This is not an allergy to gluten or wheat but may be an indicator of celiac disease and requires testing.

Most food intolerances are diagnosed through trial and error to determine which foods cause problems. Treatment usually includes avoiding that food, learning how much of the food you can tolerate or simply treating the symptoms when you do eat a problem food. Food intolerances generally are not life-threatening, but true food allergies can be.

Anita Marlay, R.D., L.D., is a dietitian in the Cardiopulmonary Rehab Department at Lake Regional Health System in Osage Beach, Mo.