# 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](https://www.healthline.com/nutrition/common-food-allergies), 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](https://medlineplus.gov/ency/article/000844.htm#:~:text=Anaphylaxis%20is%20a%20severe%2C%20whole,system%20becomes%20sensitized%20to%20it.), which is severe and can be life-threatening. Identifying a food allergy may involve a [skin prick test](https://www.mayoclinic.org/tests-procedures/allergy-tests/about/pac-20392895#:~:text=A%20skin%20prick%20test%2C%20also,usually%20done%20on%20the%20forearm.), where an allergist pricks the skin’s surface with an allergen to see if there’s a positive reaction, or with a [blood test](https://medlineplus.gov/lab-tests/allergy-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](https://my.clevelandclinic.org/health/diseases/21688-food-intolerance). While there isn’t a test for every intolerance, they can be diagnosed through an [elimination diet](https://www.healthline.com/nutrition/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.