The big distinction? Allergies can be life-threatening and intolerances usually aren't, says Carla McGuire Davis, MD , associate professor of pediatrics in immunology, allergy, and rheumatology at Baylor College of Medicine. That's why you can usually eat quite a bit of a food to which you're intolerant before having a reaction, while just a few bites of a food that you're allergic to can set you off. Hopefully, you already know if you have a life-threatening food allergy (and keep an EpiPen or another type of injectable epinephrine handy). But, even non-fatal allergies can be severe — and they're still important to diagnose and manage, Dr. Davis says. And part of that management is watching out for changes in how your body reacts to certain foods. Unfortunately, it's possible to develop a food allergy well into adulthood.