Food allergy or food intolerance? How to tell the difference and what to do

The short answer

A food allergy is a reaction of the immune system, the body's defense against germs. A tiny amount of the food can cause hives, swelling, vomiting, wheezing or a drop in blood pressure. A severe allergic reaction, called anaphylaxis, can kill. A food intolerance happens in the digestive system. It causes gas, bloating, cramps or diarrhea, usually depends on how much you ate, and is not life-threatening.

The difference changes what you do next:

• Allergy: strict avoidance, careful label reading, and an emergency plan with epinephrine if a clinician prescribes it.
• Intolerance: many people can still eat some of the food and only need to manage the amount.
• Celiac disease is a third kind of problem: an immune reaction to gluten that damages the small intestine. It needs strict gluten avoidance, but it does not cause anaphylaxis.

Only a clinician can confirm which one you have. In a national survey of more than 40,000 U.S. adults (2015–2016), about 1 in 5 said they had a food allergy, but only about 1 in 10 described symptoms that fit one.

Signs of a serious allergic reaction

Allergic reactions to food usually start within minutes to 2 hours of eating. Anaphylaxis often affects more than one part of the body at once:

• Skin: hives, itching, redness, or swelling of the lips, face, tongue or eyes
• Mouth and throat: itching, throat tightness, a hoarse voice, trouble swallowing
• Breathing: wheezing, coughing, shortness of breath
• Stomach: vomiting, cramps, diarrhea
• Heart and circulation: dizziness, fainting, a weak pulse
• A feeling that something terrible is about to happen

If you have an allergist's written action plan, follow it. Guidance from U.S. allergy specialists (2023) says an ambulance may not always be needed when a reaction clears quickly and completely after one dose and more help is close by; ask your allergist whether your plan covers this. With no plan, or a reaction that is severe, does not fully clear or comes back, call 911.

A mild reaction last time does not promise a mild one next time. The CDC notes that symptoms and their severity can change over time in the same person.

Allergy and intolerance, side by side

Stomach symptoms appear in both columns. Speed, a small amount of food, and symptoms outside the gut (hives, swelling, trouble breathing) point toward allergy.

Write down what happened

Testing is most useful when your history guides it. Before an appointment, note:

• What you ate, roughly how much, and whether it was raw or cooked
• How long until symptoms started, and how long they lasted
• Which symptoms, in which parts of the body
• Whether it happens every time you eat that food
• Anything else you ate or took around the same time, and a photo of any rash

Patterns that confuse people:

• A delayed allergy to red meat. Alpha-gal syndrome is a serious allergy that can develop after a tick bite. The CDC says symptoms usually appear 2 to 6 hours after eating red meat (such as beef, pork or lamb) or dairy, and can include anaphylaxis, so the delay can hide the link.
• An itchy mouth from raw fruits or vegetables. In oral allergy syndrome, proteins in some raw produce resemble pollen. Cooking usually prevents it, and severe reactions are rare. If you also have hay fever, see understanding and managing seasonal allergies.
• Slow-building allergic conditions. Some, such as eosinophilic esophagitis (an inflamed esophagus), are not clearly tied to one meal.
• Food poisoning. If several people got sick after one meal, suspect a germ; see how long leftovers last in the refrigerator.

Two common look-alikes: milk and wheat

Lactose intolerance or milk allergy?

Lactose intolerance means your small intestine makes too little lactase, the enzyme that digests lactose, the natural sugar in milk. Within a few hours of dairy you may have bloating, gas, diarrhea, nausea or stomach pain. The National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) says most people with it do not need to avoid lactose completely. Many can have about 12 grams of lactose, roughly 1 cup of milk, with mild symptoms or none. Small servings with meals, yogurt and hard cheeses (lower in lactose), lactose-free milk and lactase enzyme products can help. If you cut out dairy, ask how to get enough calcium and vitamin D.

Milk allergy is an immune reaction to the proteins in milk, and it usually shows up in the first year of life. Lactose-free milk is still cow's milk with the lactose broken down, so the proteins that cause milk allergy are still there. Federal rules also allow "non-dairy" products to contain caseinates, which are milk proteins, and "dairy-free" has no legal definition. Read the ingredient list instead.

Irritable bowel syndrome (IBS), celiac disease and other gut conditions can look like lactose intolerance, so get checked rather than guess.

Celiac disease, wheat allergy or gluten sensitivity?

Gluten is a protein in wheat, barley and rye.

Keep eating gluten until you have been tested for celiac disease. NIDDK warns that a gluten-free diet can affect the test results. If you have already stopped, tell the clinician before testing.

Tests that help, and tests to skip

Tests that help, when your history points to them:

• Skin prick tests and blood tests for IgE show whether your body has made IgE antibodies to a food. A positive result alone does not prove an allergy; many people who test positive are not allergic. If you eat a food regularly without symptoms, ask your allergist before you stop because of a test.
• An oral food challenge means eating small, increasing amounts of the food while a clinician watches. It can confirm or rule out an allergy and must be done under medical supervision. Never test a suspected allergy by eating the food on your own.
• A hydrogen breath test checks for lactose intolerance; celiac blood tests need you to still be eating gluten.

Tests to skip: IgG "food sensitivity" panels. The American Academy of Allergy, Asthma & Immunology (AAAAI) says IgG to foods is likely a normal response to eating them and has never been proven to diagnose an allergy or an intolerance. AAAAI and the Canadian Society of Allergy and Clinical Immunology recommend against using it for either. AAAAI's Choosing Wisely list also advises against broad IgE test batteries your history does not support. The risk is cutting out foods you do not need to avoid. Elimination diets can help spot milder reactions but are not used after a severe one; do them with a clinician or dietitian.

Reading labels when someone has a food allergy

U.S. law names nine major food allergens: milk, eggs, fish, crustacean shellfish (such as shrimp, crab and lobster), tree nuts, peanuts, wheat, soybeans and sesame. The Food Allergen Labeling and Consumer Protection Act of 2004 required foods labeled on or after January 1, 2006, to declare the first eight. The FASTER Act, signed April 23, 2021, added sesame for foods sold across state lines on or after January 1, 2023.

A major allergen appears either inside the ingredient list, such as "whey (milk)", or in a "Contains:" line next to it. The label must name the specific tree nut, fish or shellfish, such as "almond" or "shrimp".

What a label will not tell you:

• "May contain" and "made in a facility with" warnings are voluntary and not standardized. Leaving one off does not make a food safe. The NIAID guidelines summary suggests that people with food allergy avoid products carrying these warnings; ask your allergist how to handle them.
• Highly refined oils made from a major allergen are exempt, and so are fresh fruits and vegetables. Ask your allergist whether any oils matter for you.
• Barley and rye are not major allergens, so a "Contains: wheat" line will not flag them. For celiac disease, read the whole ingredient list or look for a "gluten-free" claim. Under Food and Drug Administration (FDA) rules, that claim means any unavoidable gluten is below 20 parts per million.
• Milk and eggs from other animals count. Under FDA guidance from January 2025, milk from goats, sheep and similar animals counts as "milk," and eggs from ducks, quail and other birds count as "egg."

Read the label each time you buy a product, even a familiar one. Foods are sometimes recalled because they contain an allergen that is not on the label; see how to check whether a product, medicine or food has been recalled.

In California, restaurants: since July 1, 2026, chains covered by federal menu calorie-labeling rules (generally 20 or more locations under one name) must give written notice of which of the nine major allergens are in each menu item, on the menu or in a digital menu with a printed alternative. Some mobile carts and non-permanent food facilities are exempt. The law does not require cross-contact warnings, so still tell staff about the allergy and ask how food is prepared.

Planning shared meals at home around an allergy

Most households cannot cook two dinners a night. These steps build on household guidance from Food Allergy Research & Education (FARE), a nonprofit. Cross-contact means one food touches another and their proteins mix. Cooking does not remove an allergen from food.

1. Agree on a house rule. Some families keep the allergen out of the home; others keep it with set precautions. Weigh past reactions, the ages of children, and how hard removing the food would be for everyone else.
2. Store and label. Give safe foods their own shelf in the pantry and refrigerator, use sealed containers, and mark safe items with colored stickers.
3. Cook the safe food first. Keep it covered and away from splatter. Use separate utensils, cutting boards and serving spoons; one color for "safe" tools helps.
4. Wash with soap and water. Plain water and hand sanitizer do not remove food allergens. In one study, peanut allergen was still found on 6 of 12 hands after hand sanitizer. Clean counters and tables with soap and water or an all-purpose cleaner.
5. Build one shared meal when you can. Start from a dish without the allergen and let others add it at the table, such as cheese or nuts served on the side. Serve the person with the allergy first.
6. Make the plan everyone's job. Everyone at home should be able to read a label and know the emergency plan. Keep epinephrine in a known spot, plus a travel kit. MedlinePlus advises that anyone who has had a serious or whole-body reaction carry two epinephrine devices at all times.
7. Plan for gatherings. Ask guests to keep packaging so you can read labels, and bring a dish you know is safe to potlucks.

For celiac disease, the same kitchen habits apply, because small amounts of gluten can keep symptoms going. For lactose intolerance, households can usually share meals and keep lactose-free milk on hand.

Who to ask, and what to ask

• Call 911 for the anaphylaxis signs above.
• See a clinician soon after any reaction with hives, swelling or breathing symptoms, even one that went away on its own. Ask whether you need an allergist and an epinephrine prescription.
• Book a visit if digestive symptoms keep coming back, or before you cut out a whole food group. Go sooner for weight loss, anemia, rectal bleeding, or black or bloody stools; NIDDK lists these as signs that something other than IBS may be going on.
• Who can help: a primary care clinician first, then an allergist, a gastroenterologist (for celiac disease or ongoing gut symptoms) or a registered dietitian. If you need a regular clinician, see how to find a primary care doctor who is accepting new patients.

Questions to bring:

• Does my history sound like an allergy, an intolerance or something else?
• Which tests make sense, and what can a positive result not tell me?
• Do I need epinephrine, how many devices should I carry, and can I have a written action plan?
• How should I treat "may contain" labels?
• Should I keep eating gluten until celiac testing is done?
• Are treatments such as supervised desensitization or medicine an option for me?

If the reaction followed a medicine rather than a food, see medication side effect, allergy or intolerance.

A common question

Can a food allergy start in adulthood?

Yes. In the 2015–2016 national survey, about half of adults with a convincing food allergy said at least one of their allergies began in adulthood.

Sources

1. Guidelines for the Diagnosis and Management of Food Allergy in the United States: Summary for Patients, Families, and Caregivers — National Institute of Allergy and Infectious Diseases (NIAID), NIH Publication No. 11-7699, May 2011; accessed October 21, 2026.
2. Food Allergy — NIAID; accessed October 21, 2026.
3. Food Intolerance Versus Food Allergy — American Academy of Allergy, Asthma & Immunology (AAAAI); accessed October 21, 2026.
4. Anaphylaxis — AAAAI; accessed October 21, 2026.
5. The Myth of IgG Food Panel Testing — AAAAI; accessed October 21, 2026.
6. Choosing Wisely: Some Tests and Procedures Are Over or Misused to Diagnose and Treat Allergies, Asthma and Immunologic Disorders — AAAAI, released April 4, 2012; accessed October 21, 2026.
7. Anaphylaxis: A 2023 Practice Parameter Update — Golden DBK and others, Annals of Allergy, Asthma & Immunology, 2023 (AAAAI/ACAAI Joint Task Force on Practice Parameters); accessed October 21, 2026.
8. Anaphylaxis — MedlinePlus Medical Encyclopedia, U.S. National Library of Medicine, reviewed January 20, 2026; accessed October 21, 2026.
9. Food allergy — MedlinePlus Medical Encyclopedia, reviewed October 29, 2024; accessed October 21, 2026.
10. Gluten Sensitivity — MedlinePlus, updated May 28, 2024; accessed October 21, 2026.
11. Food Allergies in Schools — Centers for Disease Control and Prevention (CDC), July 9, 2024; accessed October 21, 2026.
12. About Alpha-gal Syndrome and Symptoms of Alpha-gal Syndrome — CDC, reviewed January 5, 2026; accessed October 21, 2026.
13. Symptoms & Causes of Lactose Intolerance, Diagnosis and Eating, Diet, & Nutrition — National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK), reviewed February 2018; accessed October 21, 2026.
14. Definition & Facts for Celiac Disease, Diagnosis and Treatment — NIDDK, reviewed October 2020; accessed October 21, 2026.
15. Diagnosis of Irritable Bowel Syndrome — NIDDK, reviewed November 2017; accessed October 21, 2026.
16. Non-Celiac Gluten Sensitivity — UCLA Health; accessed October 21, 2026.
17. Public Law 108-282, Title II: Food Allergen Labeling and Consumer Protection Act of 2004 — U.S. Government Publishing Office, approved August 2, 2004; accessed October 21, 2026.
18. Public Law 117-11: FASTER Act of 2021 — U.S. Government Publishing Office, approved April 23, 2021; accessed October 21, 2026.
19. 21 CFR 101.91, Gluten-free labeling of food — Electronic Code of Federal Regulations, current as of October 16, 2026; accessed October 21, 2026.
20. Update: FDA Guidance on Food Allergen Labeling — Food Allergy Research & Education (FARE), February 7, 2025; accessed October 21, 2026.
21. Dairy-Free and Non-Dairy — Food Allergy Research and Resource Program, University of Nebraska–Lincoln; accessed October 21, 2026.
22. California SB 68 (2025), chaptered text, Chapter 741, Statutes of 2025 — California Legislature, via LegiScan, chaptered October 13, 2025; accessed October 21, 2026.
23. Cleaning Methods, How to Avoid Cross-Contact and Creating a Food Allergy Safety Zone at Home — FARE; accessed October 21, 2026.
24. Prevalence and Severity of Food Allergies Among US Adults — Gupta RS and others, JAMA Network Open, January 4, 2019; accessed October 21, 2026.
25. Recognize and Respond to Anaphylaxis — Food Allergy Research & Education (FARE), 2025; accessed October 22, 2026.