The words allergy, intolerance, and sensitivity are used interchangeably in ordinary conversation and rarely in medical settings. The distinctions matter, because the mechanisms are different, the risks are different, and the tests that identify them are different. Getting them mixed up leads to unnecessary restriction on one end and dangerous complacency on the other.
Roughly 8 percent of children and 10 percent of adults in the United States have a true food allergy. Many more people believe they do; surveys consistently find that self-reported food reactions are two to three times more common than confirmed ones. Sorting out what is going on takes some care.
Allergy: the immune system misfires
A food allergy is an immune response, typically mediated by IgE antibodies, that treats a harmless food protein as a threat. Symptoms appear within minutes to a couple of hours and can include hives, swelling, vomiting, wheezing, and, in severe cases, anaphylaxis. Anaphylaxis is life-threatening and requires epinephrine.
The major food allergens account for the vast majority of reactions: milk, egg, peanut, tree nuts, wheat, soy, fish, shellfish, and, added by the FDA in 2023, sesame. Peanut, tree nut, and shellfish allergies tend to persist into adulthood; many milk, egg, wheat, and soy allergies resolve in childhood.
Diagnosis relies on a careful history, skin-prick testing, and IgE blood tests, sometimes confirmed by an oral food challenge in a medical setting. IgE tests have high false-positive rates when used as screening; a positive result without symptoms often does not indicate a real allergy.
Intolerance: the body cannot process it well
A food intolerance is not an immune reaction. It reflects the body's inability to digest or metabolize something efficiently. Symptoms are typically gastrointestinal, appear more slowly, and depend on dose. Intolerance is unpleasant but not dangerous.
The clearest example is lactose intolerance, caused by reduced production of the enzyme lactase after childhood. Most of the world's adults have some degree of it. Small amounts of lactose, hard cheeses, and yogurt are usually tolerated; lactase supplements help.
Other recognized intolerances include:
- FODMAP sensitivity, in which fermentable carbohydrates trigger bloating and altered bowel habits, especially in irritable bowel syndrome.
- Histamine intolerance, less well characterized, sometimes implicated in reactions to aged cheeses, wine, and cured meats.
- Non-celiac gluten sensitivity, a genuine but poorly understood category that requires ruling out celiac disease first.
Celiac disease is not an intolerance; it is an autoimmune disease that damages the small intestine. It requires biopsy or specific antibody testing while still eating gluten.
"Sensitivity": mostly not what tests claim
The term food sensitivity is used loosely and has no standardized medical definition. It is the category most abused by direct-to-consumer testing companies that sell IgG panels claiming to identify problem foods. IgG antibodies to food are markers of exposure, not disease. The American Academy of Allergy, Asthma and Immunology, along with equivalent bodies in Europe and Canada, explicitly recommends against these tests. They produce long lists of foods to avoid, drive unnecessary restriction, and can worsen relationships with food.
Hair analysis, applied kinesiology, electrodermal testing, and pulse tests have similarly no scientific basis. If you are told to eliminate ten foods based on a mail-in test, be skeptical.
What to actually do
If you suspect a food is causing symptoms:
- Track it. Keep a two- to four-week food and symptom diary before eliminating anything. Patterns are often less obvious than they feel.
- See a specialist, ideally a board-certified allergist for suspected allergy or a gastroenterologist for suspected intolerance or celiac disease.
- Do not stop eating gluten before testing for celiac disease; it makes the test unreliable.
- Try structured elimination diets under supervision, especially the low-FODMAP protocol for IBS, which is designed to be reintroduced systematically rather than followed forever.
- Ignore IgG food panels. Money and attention are better spent elsewhere.
Restricting food is not free; it costs nutrients, social ease, and, for children, sometimes tolerance itself. Restriction should be proportionate to evidence.