Food intolerance vs. food allergy: What's the difference?

Q: What's the difference between a food intolerance and food allergy?

Charlotte / Maine

Although many people have adverse reactions to certain foods, true food allergy — a reaction triggered by the immune system — is uncommon. Only about 2 percent of adults and 6 percent of children have a true food allergy. Far more people have a food intolerance, unpleasant symptoms triggered by certain foods. Unlike a food allergy, a food intolerance doesn't involve the immune system.

Lactose intolerance is one example of a food intolerance. People with lactose intolerance lack the enzyme lactase needed to digest milk sugar (lactose) in milk and other dairy foods. This inability to break down lactose during digestion may cause diarrhea, gas, bloating and abdominal pain.

In a food allergy, your immune system mistakenly identifies a specific food or a component of a food as a harmful substance. Your immune system triggers certain cells to produce immunoglobulin E (IgE) antibodies to fight the culprit food or food component. The next time you eat even the smallest amount of that food, the IgE antibodies sense it and signal your immune system to release histamine and other chemicals into your bloodstream. Signs and symptoms of a food allergy may include tingling in the mouth, hives, swelling of the lips, face, tongue and throat, wheezing or breathing difficulties, and dizziness or fainting.

It's important to distinguish food intolerance from food allergy. If you have a food allergy, eating even the tiniest amount of the food may trigger a serious allergic reaction. By contrast, if you have a food intolerance, you usually can eat small amounts of the food without a reaction.

If you have a reaction to a particular food, tell your doctor about it. Tests can help determine whether you have a food allergy.