Signs vary: a true wheat allergy causes immediate hives, itching, swelling, wheeze or anaphylaxis soon after eating. Celiac disease causes immune damage with diarrhea, bloating, abdominal pain, weight loss, anemia, fatigue and sometimes a blistering skin rash; it's diagnosed by blood tests and intestinal biopsy. Non‑celiac gluten sensitivity causes bloating, brain fog, headache and fatigue without positive tests. See a doctor before starting a gluten‑free diet.

Gluten is found in wheat and related grains—bread, pasta, cereals, pastries, cakes, biscuits, crackers, couscous, bulgur, semolina and products made from spelt, kamut, farro or triticale. Barley (malt, malt vinegar, beer) and rye (rye bread, crispbreads) contain gluten. Many processed foods—soups, sauces, salad dressings, soy sauce, processed meats and some candies—may also contain hidden gluten; oats can be contaminated unless labeled gluten-free.

The main cause is an abnormal immune reaction to gluten proteins found in wheat, barley and rye. In celiac disease, gluten (especially gliadin) triggers an autoimmune response in genetically susceptible people (HLA‑DQ2 or HLA‑DQ8), damaging the intestine. Wheat allergy is a separate IgE‑mediated reaction to wheat proteins; non‑celiac gluten sensitivity has less well‑defined mechanisms.

Get proper diagnosis (blood tests/biopsy or allergy testing). If confirmed, avoid all gluten-containing foods (wheat, barley, rye); read labels and prevent cross-contamination. Use certified gluten-free grains (rice, quinoa, gluten-free oats). Replace nutrients with fortified foods or supplements and consult a dietitian. For IgE-mediated wheat allergy carry an epinephrine auto-injector and antihistamines; maintain medical follow-up.

Six common symptoms of a person with a gluten allergy are abdominal pain and cramping, bloating and excessive gas, chronic diarrhea, constipation, persistent fatigue and brain fog, and unexplained weight loss or iron‑deficiency anemia. Symptoms can vary by person and may overlap with other conditions; medical evaluation is recommended for diagnosis and appropriate testing.

To test for a "gluten allergy," see a doctor. For celiac disease, blood tests (tTG‑IgA plus total IgA, or DGP/tTG‑IgG if IgA deficient) must be done while you’re still eating gluten; a small‑bowel biopsy confirms diagnosis. For IgE‑mediated wheat allergy, skin‑prick testing or specific IgE blood tests are used. Non‑celiac gluten sensitivity is diagnosed by excluding other conditions and a supervised elimination and re‑challenge.