Food Allergy vs. Food Sensitivity vs. Intolerance

Food Allergy: An Immune System Reaction

A true food allergy happens when the immune system mistakes a food protein for a threat. In the most common type, the body makes IgE antibodies against that protein. The next time you eat it, those antibodies trigger the release of histamine and other chemicals, usually within minutes to two hours.

Symptoms can include hives, swelling of the lips or face, vomiting, wheezing and, in severe cases, anaphylaxis. Because reactions can escalate quickly, a suspected food allergy should always be evaluated by a qualified provider. The National Library of Medicine has a clear overview of how food allergy testing works, and most reactions trace back to a short list of common food allergens like milk, egg, peanut, shellfish and sesame.

Allergy blood tests measure allergen-specific IgE, and skin prick tests look for a raised bump where a small amount of allergen is introduced. Neither test alone confirms an allergy. Results are read alongside your symptoms and history, and sometimes an oral food challenge in a clinic. If you want to see what a typical blood test report looks like, our sample food allergy results walk through the levels and classes.

Food Intolerance: A Digestive Problem

A food intolerance doesn't involve the immune system. It happens when your digestive system has trouble breaking down a food. The classic example is lactose intolerance, where the body doesn't make enough lactase, the enzyme that digests milk sugar.

Intolerance symptoms are mostly digestive: gas, bloating, cramping and diarrhea. They're uncomfortable but not dangerous, and they often depend on how much you eat. Someone with lactose intolerance might handle a splash of milk in coffee but struggle with a bowl of ice cream. Someone with a milk allergy usually can't tolerate even small amounts.

Food Sensitivity: The Gray Area

"Food sensitivity" is a looser term. It's often used for delayed, hard-to-pin-down symptoms like fatigue, brain fog, headaches or skin flare-ups. Many at-home sensitivity kits measure IgG antibodies to dozens of foods, but major allergy organizations don't recommend IgG testing for diagnosis, because IgG often just reflects foods you eat regularly.

If you suspect a sensitivity, a structured elimination diet guided by a provider or dietitian is usually more useful than a long panel of IgG results. It's also worth ruling out conditions that look similar, such as celiac disease, which is an autoimmune reaction to gluten and needs its own testing.

Quick Comparison

Which Test Should You Ask For?

If your symptoms come on fast, involve your skin or breathing, or have ever been severe, start with an allergist and IgE-based testing. If your symptoms are mostly digestive and seem dose-dependent, ask about intolerance testing. And if your reactions are to raw fruits and vegetables and stay in your mouth and throat, you may be dealing with pollen-related cross-reactivity, which we cover in our guide to fruit allergies and oral allergy syndrome.

Adults aren't off the hook, either. Allergies can start at any age, and some of the most common ones in men, like shellfish, often appear for the first time in adulthood. Read more in our guides to food allergies and men's health and food allergies and women's health.