Many people confuse food allergies and food intolerance, and it is easy to do. Allergies and intolerance to foods can cause some of the same symptoms. However, food allergies can cause life-threatening reactions, while food intolerances cannot.

What Are the Most 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 particularly intense. The eight major food allergens are:

• Eggs
• Fish
• Milk
• Peanuts
• Shellfish
• Soybeans
• Tree nuts
• Wheat

What Are the Most Common Food Intolerances?

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

• Lactose in dairy products
• Gluten in grain products
• Sulfites, a common preservative in food and hygiene products
• Food coloring dyes, especially yellow dye number 5
• Monosodium glutamate (MSG), a common flavor enhancer

How To Tell 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, while food allergies can cause a much wider array of symptoms in multiple body systems. 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 an epinephrine auto-injector followed by a trip to the emergency room. Food intolerance cannot trigger anaphylaxis.

Read more details about food allergy symptoms.

Reactions to food allergies usually happen within two hours of eating an allergenic food, often much faster. Reactions to food intolerance can be delayed as long as 20 hours after ingesting a food to which someone is intolerant.

Another key difference between food allergy and food intolerance is that when a person 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 of it without experiencing symptoms.

Causes of Food Allergy vs. Food Intolerance

The development of both food allergy and food intolerance is influenced by genetic factors. Both conditions tend to run in families.

Food allergy is a dysfunction of the immune system. In food allergy, the immune system mistakenly identifies proteins in a particular food as a dangerous, invading antigen. When a person with a food allergy eats the allergenic food, their immune system recognizes it and launches an attack that involves triggering inflammatory chemicals that flood the body, causing allergy symptoms. Read more about causes and risk factors for food allergy.

Food intolerance is a dysfunction of the gastrointestinal system. In food intolerance, the body is unable to fully digest a food. Celiac disease is a bit more complicated. Celiac disease is caused by an autoimmune condition that leads to the inability to tolerate any amount of gluten, a protein found in many grains.

Some food intolerances, are caused by a lack of a particular enzyme needed to digest the food in question. For example, lactose is a sugar found in milk and some other dairy foods. Lactase is the enzyme needed to digest lactose. 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. Celiac disease requires complete avoidance of gluten to prevent a severe gastrointestinal reaction.

Diagnosis of Food Allergy vs. Food Intolerance

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

It is 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 avoid symptoms of a food allergy is to completely avoid the food. If an allergic person comes into contact with their allergenic food, antihistamines or corticosteroids may improve mild symptoms, but an emergency injection of 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 intolerance do not need to worry about completely avoiding the food to which they are intolerant, but only limiting the amount. People with lactose intolerance can take extra lactase enzymes, branded as Lactaid, to help them digest dairy products.

Is it Possible To Have Both Food Allergies and Food Intolerance?

Yes. Many people with food allergies also suffer from food intolerances such as lactose intolerance or gluten sensitivity.

Condition Guide

• Food Allergies: An Overview
• Food Allergy Symptoms
• Food Allergy — The Path to Diagnosis
• Medications for Food Allergy Symptoms
• Types of Food Allergies
• What Causes Food Allergies?