How Do Food Allergies and Food Intolerances Differ?

It can be easy to confuse food allergies and food intolerances. But there are some key differences:

A food intolerance happens when the body can't properly digest a food, or the food might irritate the digestive system. Food intolerances, such as lactose intolerance and celiac disease, can make someone feel ill with symptoms such as nausea, gas, cramps, belly pain, diarrhea, irritability, or headaches.

A food allergy happens when the body's immune system, which normally fights infections, sees a food that is usually harmless as an invader. This leads to an allergic reaction — an immune system response in which chemicals like histamine are released in the body. The reaction can cause symptoms like hives, vomiting, belly pain, throat tightness, hoarseness, coughing, breathing problems, or a drop in blood pressure. Some severe reactions (called anaphylaxis) can be life-threatening.

Even if previous reactions have been mild, someone with a food allergy is always at risk for the next reaction being life-threatening. Eating just a microscopic amount of the food could lead to anaphylaxis. So anyone with a food allergy must avoid the problem food(s) entirely and always carry emergency epinephrine.

People with food sensitivities, on the other hand, might be able to ingest a small amount of the bothersome food without a problem.