What’s the Difference Between a Food Allergy and a Food Intolerance?

If drinking milk upsets your stomach or causes hives, it could be a food allergy or intolerance. Knowing which one can make a difference.

“Food intolerances aren’t as dangerous as food allergies,” says Karen Hsu Blatman, MD, an allergist at Dartmouth Hitchcock Medical Center (DHMC). “They usually cause discomfort, not life-threatening reactions.”

In the U.S., about 6.7% of adults have food allergies, and around 20% experience food intolerances.

Food intolerances can cause symptoms similar to allergies, making it easy to confuse the two.

How can you tell the difference?

What causes food allergies?

“Food allergies happen when the immune system identifies certain foods as threats, which can lead to serious reactions,” Hsu Blatman says.

If you’re allergic to pine nuts or cow’s milk, your immune system creates a reaction using antibodies called IgE, releasing chemicals that can cause symptoms like hives or trouble breathing.

Milder food allergy symptoms include stomach discomfort or itching on your face, neck, or chest.

What are common food allergies?

The following foods cause most food allergies. By law, these foods must be clearly listed on all packaged foods.

• Shellfish: The most common adult food allergy.
• Cow’s milk: Most common in babies and young children, and many outgrow it.
• Peanuts: Usually a lifelong allergy and can cause severe reactions.
• Tree nuts: This group includes almonds, cashews, walnuts, pecans, and pistachios. Tree nut allergies are usually lifelong.
• Eggs: Common in childhood and often outgrown.
• Finfish: Allergies to fish such as salmon, tuna, and cod often start in adulthood and usually last for life.
• Sesame: This allergy can cause severe reactions, and cases have recently increased.

What about food intolerance?

A food intolerance or sensitivity usually happens because your body lacks a certain enzyme.

“Your body doesn’t make enough of the right enzyme to break down certain foods,” Hsu Blatman explains.

You might have fewer enzymes because of aging or certain health conditions. Without enough lactase (an enzyme), your body cannot break down lactose, or milk sugar, into simple sugars. 

The undigested sugar moves to your large intestine, where bacteria cause gas, bloating, and pain, Hsu Blatman explains.

Common food intolerances include:

• Dairy (lactose intolerance): Difficulty breaking down milk sugar.
• Fruit sugar (fructose intolerance): Difficulty processing sugars in fruits and honey.
• Table sugar (sucrase deficiency): Difficulty digesting table sugar and some starches.

Also, you might think you have a gluten sensitivity when it could be a problem with fructans, Hsu Blatman says.

Fructans are a type of carbohydrate found naturally in foods like wheat, onions, and garlic that can be difficult to digest.

Gluten is a protein and fructans are carbohydrates. Both can cause similar symptoms, including bloating, abdominal pain, gas, and diarrhea.

Does gut health make a difference?

Your gut health plays an important part in how well you digest food and can help protect you from food intolerances.

But chronic stress, eating processed foods, and medications like antibiotics and ibuprofen can upset your gut health and make food intolerances more likely.

Research shows that antibiotics can wipe out the “good” bacteria in your gut, changing the immune response to foods like gluten.

“Antibiotics can affect the gut microbiome, killing off good and bad bacteria. But you want a healthy balance for proper digestion,” says Jamie M. Horrigan, MD, a gastroenterology fellow at DHMC.

The foods you choose can also change the balance of bacteria in your gut.

“Try to eat fewer processed foods and meats, and more fresh fruits and vegetables,” Horrigan says. “You want to diversify your food intake and help diversify your gut microbiome.”

Does allergy testing help?

You can treat food allergies with prescription medication like omalizumab and food oral immunotherapy, says Marcus S. Shaker, MD, an allergist at DHMC.

To confirm if you have an allergy, you can start with an allergy test.

“No test is perfect, and sometimes positive results may not reflect a true allergy, especially if there hasn’t been a reaction,” Shaker explains.

Allergy tests include:

Skin prick test

• A small drop of the suspected allergen is placed on your forearm or back.
• The skin is gently scratched so the allergen enters just beneath the surface.

IgE blood test

• Measures the number of allergy-related antibodies in your blood.
• IgE shows sensitization, and experts typically don’t recommend a blood test unless you’ve had a reaction.
• A doctor should review your test results alongside your medical history and symptoms.

Oral food challenge

• Performed under strict medical supervision.
• You eat very small, gradually increasing amounts of the suspected food while doctors monitor for any signs of a reaction.

Does the environment play a role?

Environmental factors and climate change can affect food allergies and even create new ones.

“Change is constant,” Shaker says.

For example, some tick bites can lead to a delayed meat allergy called alpha-gal syndrome.

Other environmental allergens, like pollen, can affect how your body reacts to certain foods.

Research shows that pollen food allergy syndrome happens when proteins in raw fruits, vegetables, or nuts are similar to proteins in plant pollen. Your immune system mixes them up and reacts to the food.

What about gluten and celiac disease?

Celiac disease is an autoimmune disorder, not a food allergy or intolerance.

If you have celiac disease and eat gluten, your immune system attacks the lining of your small intestine.

Celiac disease can cause digestive problems, lead to nutrient deficiencies, and further lead to serious health issues.

“The trick with diagnosing celiac is that you have to be eating gluten, ideally for at least two to six weeks, before we can reliably test for it,” Horrigan says.

If you’re cutting foods like wheat bread or milk to manage potential allergies or intolerances, Horrigan says support is available.

“We don’t want you restricting your diet so much that you can't eat anything. There are dietitians, gastroenterologists, and doctors who can help you,” she says.

If you suspect a food allergy or intolerance:

Watch for any symptoms that show up after you eat.

Contact your doctor for an appointment.

Call 911 immediately if you have swelling in your throat, low blood pressure, or trouble breathing.

Resources and Related Stories

Dartmouth Health Allergy Clinic at DHMC

Food Allergy Research and Education

How Much Fiber Do You Need?

What Sugar Does to The Body

Food Allergy Prevention May Be Hiding in Kitchen Cupboards