Can a food allergy upset your stomach?

How allergies cause it

Vomiting or cramps after a meal can be a food allergy at work. Food allergens are parts of food, usually proteins, that immune cells recognize, and when an immune cell binds to one, a reaction occurs that causes the symptoms of food allergy.⁴

How an allergen gets in shapes the symptoms. If you eat the allergen, you are more likely to have symptoms in your mouth, stomach and intestines, and food allergies are the most likely allergies to cause nausea or vomiting.¹ FDA’s list of food allergy symptoms includes vomiting, diarrhea and abdominal cramps, along with hives, a tingling or itchy mouth and swelling of the face, tongue or lips.² Many reactions start with skin symptoms, like hives or a rash, but some do not.³

Typical food allergy reactions come on fast. Symptoms usually start as soon as a few minutes after eating and as long as two hours after.³ FDA names nine major food allergens: milk, eggs, fish, crustacean shellfish, tree nuts, peanuts, wheat, soybeans and sesame.²

Some food allergies are delayed. Food protein-induced enterocolitis syndrome (FPIES) is a severe condition that causes vomiting and diarrhea, and its reactions come within hours after eating the trigger food.⁵ FPIES often develops in infancy, usually when a baby is introduced to solid food or formula, but it is being recognized more often in adults as well.⁵ In some cases, symptoms can progress to dehydration and shock brought on by low blood pressure and poor blood circulation.⁵

Allergies or something else?

Many people may think they have a food allergy when what they are really experiencing is a food intolerance.¹ The two work differently. Food allergies involve your immune system and can be life-threatening, while an intolerance is when your body has trouble digesting a food.³ Food intolerances do not involve the immune system.⁴ An intolerance can mimic a food allergy, causing nausea and vomiting, but it is not life-threatening.¹

Lactose intolerance is a familiar example. Its symptoms may include bloating, diarrhea, gas, nausea and pain in your abdomen, and it is caused by lactose malabsorption: the small intestine makes low levels of lactase and can’t digest all the lactose you eat or drink.⁶ It is different from a milk allergy, which is an immune system disorder.⁷

The amount eaten can be a clue. Most people with lactose intolerance can consume some amount of lactose without having symptoms.⁷ With a food allergy, even trace amounts of the allergen can cause a reaction in some people.³

Seasonal allergies are an unlikely cause. Nausea and vomiting are rarely, if ever, symptoms of a seasonal allergy.¹

When to see a doctor

Stomach symptoms can be part of anaphylaxis. MedlinePlus lists vomiting, diarrhea and cramps among its signs, along with chest symptoms such as wheezing and mouth and throat symptoms such as swollen lips or tongue and throat tightness. It says to call 911 for a serious allergic reaction.⁸

NIAID’s food allergy guidelines say a health care professional should consider food allergy if you have a combination of symptoms within minutes to hours after eating food, after eating a specific food on more than one occasion, or both.⁴ A suspected food allergy needs a professional diagnosis: self-reports of presumed food allergy must be confirmed by a health care professional.⁴

An allergist can tell an allergy from an intolerance. ACAAI says the best way to find out whether you have a food allergy is to see an allergist for testing, and that testing also helps the allergist determine whether you have a food intolerance or a food allergy.¹