What's the Difference Between a Food Allergy and Intolerance?

Dear Expert,

What’s the difference between a food allergy and intolerance, and how do I know which one I have?

Dear Anonymous,

A food allergy is an immune system reaction to an allergen, like eggs, milk, or peanuts. These reactions can affect multiple organs and cause symptoms like itching in the mouth, hives, stomach upset, and vomiting. They can also progress to anaphylaxis, which is severe and can be life-threatening.

Identifying a food allergy may involve a skin prick test, where an allergist pricks the skin’s surface with an allergen to see if there’s a positive reaction, or with a blood test. If it’s the latter, make sure that an allergist interprets the results.

Food intolerance is different. You can still eat certain foods without triggering a life-threatening reaction, but you may also be in the bathroom all day. While there isn’t a test for every intolerance, they can be diagnosed through an elimination diet. If you’re feeling symptoms related to food intolerance, I would first go to a doctor, who can rule out other causes. After that, you can think about looking at your diet.