It’s common for people to confuse food allergies and food intolerances, and it’s easy to see why — they can cause similar symptoms. However, there’s an important difference. While food intolerances can make you feel uncomfortable or unwell, food allergies can be life-threatening. Recognizing this distinction is crucial, as a food allergy could lead to an emergency, while an intolerance, though unpleasant, doesn’t carry the same risk. Understanding what’s happening with your body can be the key to managing these reactions safely.

Common Food Allergies

Nearly any food can cause an allergic reaction. However, eight food groups are responsible for 90 percent of food allergies, and reactions to these foods tend to be intense. The eight major food allergens are:

• Eggs
• Fish
• Cow’s milk
• Peanuts
• Shellfish
• Soybeans
• Tree nuts
• Wheat

Common Food Intolerances

Many foods and food additives can cause intolerance. The most common include:

• Lactose, found in dairy products
• Gluten, found in certain grain products
• Sulfites, a common preservative in food as well as shampoos, conditioners, lotions, and certain cosmetics
• Food coloring dyes, especially yellow dye number 5
• Monosodium glutamate (MSG), a common flavor enhancer

The Difference Between Food Allergy and Food Intolerance

Both food allergies and food intolerances can lead to gastrointestinal symptoms such as abdominal pain, cramping, vomiting, or diarrhea. Symptoms of food intolerance are usually limited to the digestive system and are not life-threatening. However, food allergies can cause a wider range of symptoms that affect different parts of the body. Reactions to food allergies commonly cause itching and skin rash, swelling in the mouth and throat, and asthma in addition to gastrointestinal symptoms.

Unlike food intolerance, food allergies can trigger a potentially fatal reaction called anaphylaxis. Anaphylactic reactions require immediate treatment with epinephrine followed by a trip to the emergency room. Food intolerances cannot trigger anaphylaxis.

Read more details about food allergy symptoms.

Reactions to food allergies usually happen within two hours of eating something you’re allergic to, and often even faster. In contrast, reactions to food intolerance can take much longer to show up, sometimes up to 20 hours after eating the food.

Another key difference between food allergy and food intolerance is that when someone is allergic to a food, exposure to a tiny amount — even cutting a safe food with the same knife used to cut an allergenic food — can cause a severe reaction. However, a person who is intolerant to a food can often eat a small amount without experiencing symptoms.

Causes of Food Allergy vs. Food Intolerance

Genetic factors influence the development of both food allergy and food intolerance. Both conditions tend to run in families.

A food allergy happens when the immune system mistakenly sees certain food proteins as harmful. This triggers an allergic reaction, as the body tries to fight off the perceived threat. When someone with a food allergy eats that food, their immune system releases chemicals that cause symptoms like swelling, itching, or more serious reactions.

Read more about the causes and risk factors for food allergy.

Food intolerance happens when the digestive system has trouble processing certain foods. Celiac disease is a bit more complicated. It’s an autoimmune condition where the body can’t tolerate any amount of gluten, a protein found in many grains like wheat, barley, and rye.

Some food intolerances happen because the body doesn’t have enough of the enzyme needed to properly digest certain foods. For example, lactose, a sugar found in milk and some other dairy foods, requires the enzyme lactase for digestion. People with lactose intolerance make low levels of lactase. For this reason, they may be able to eat a small amount of lactose-containing food without symptoms, but a large portion of the same food could cause intense digestive symptoms. Again, celiac disease is the exception. People with celiac disease must completely avoid gluten to prevent a reaction, which can cause symptoms like stomach problems, skin rashes, and joint pain.

Diagnosis of Food Allergy vs. Food Intolerance

Elimination diets and food challenges are used to diagnose food allergies and food intolerances. These tests are the only methods used to diagnose most food intolerances, while diagnosing food allergies usually starts with a skin prick test or a blood test to identify possible allergens. Skin and blood tests cannot identify food intolerances.

It’s possible to screen for celiac disease with a blood test, but endoscopy (insertion of a small camera into the mouth or anus to examine the intestines) may be required to confirm the diagnosis.

Read more about how food allergies are diagnosed.

Treatment of Food Allergy vs. Food Intolerance

The only safe and effective way to prevent food allergy symptoms is to completely avoid the food that triggers the allergy. If a person comes into contact with their allergenic food, antihistamines or corticosteroids may improve mild symptoms, but emergency treatment with epinephrine is the only way to halt a life-threatening anaphylactic reaction. Read more about how symptoms of food allergies are treated.

Most people with food intolerances don’t have to completely avoid the food they react to. Instead, they usually just need to limit how much they eat. People with lactose intolerance can take lactase supplements, such as Lactaid, to help digest dairy products.

Having Both Food Allergies and Food Intolerance

Many people with food allergies also have food intolerances, like lactose intolerance or gluten sensitivity. This means they may need to completely avoid certain foods because of an allergy, while they can still eat smaller amounts of other foods if they have an intolerance.

Talk to Your Doctor

Although food allergies and food intolerances can cause similar symptoms, they’re very different in terms of severity. Understanding these differences is important for staying safe and healthy. If you think you have a food allergy or intolerance, it’s a good idea to talk to your doctor for advice and a proper diagnosis. Whether you need to avoid certain foods completely or just eat smaller amounts, knowing your triggers can help you make the best choices for your health.

Find Your Team

On MyFoodAllergyTeam, the social network for people with food allergies and their loved ones, more than 41,000 members come together to ask questions, offer support and advice, and connect with others who understand life with food allergies.

Have you experienced symptoms after eating certain foods? Do you know if it was a food allergy or intolerance? What steps do you take to manage food reactions, whether it’s an allergy or intolerance? Share in the comments below, or start a conversation by posting on your Activities page.