Food allergy vs. food intolerance: What's the difference?

Food reactions are common, but most are caused by a food intolerance rather than a food allergy. A food intolerance can cause some of the same signs and symptoms as a food allergy, so people often confuse the two.

A true food allergy causes an immune system reaction that affects numerous organs in the body. It can cause a range of symptoms. In some cases, an allergic food reaction can be severe or life-threatening. In contrast, food intolerance symptoms are generally less serious and are limited to digestive problems.

If you have a food allergy, even a tiny amount of the offending food can cause an immediate, severe reaction. Digestive signs and symptoms may include nausea, vomiting, cramping and diarrhea. Other signs and symptoms can include a tingling mouth, hives, and swelling of the lips, face, tongue and throat. A life-threatening allergic reaction known as anaphylaxis can cause breathing trouble and dangerously low blood pressure. If you have a food allergy, you'll need to avoid the offending food entirely.

Food intolerance symptoms generally come on gradually and don't involve an immune system reaction. If you have a food intolerance, you may be able to eat small amounts of the offending food without trouble. You may also be able to take steps that help prevent a reaction. For example, if you have lactose intolerance, you may be able to drink lactose-free milk or take lactase enzyme pills that aid digestion (such as Lactaid).

Causes of food intolerance include:

• Absence of an enzyme needed to fully digest a food. Lactose intolerance is a common example.
• Irritable bowel syndrome. This chronic condition can cause cramping, constipation and diarrhea.
• Food poisoning. Toxins such as bacteria in spoiled food can cause severe digestive symptoms.
• Sensitivity to food additives. For example, sulfites used to preserve dried fruit, canned goods and wine can trigger asthma attacks in sensitive people.
• Recurring stress or psychological factors. Sometimes the mere thought of a food may make you sick. The reason is not fully understood.
• Celiac disease. Celiac disease has some features of a true food allergy because it does involve the immune system. However, symptoms are mostly gastrointestinal, and people with celiac disease are not at risk of anaphylaxis. This chronic digestive condition is triggered by eating gluten, a protein found in wheat and other grains.

If you have a reaction after eating a particular food, see your doctor to determine whether you have a food intolerance or a food allergy.

If you have a food allergy, you may be at risk of a life-threatening allergic reaction (anaphylaxis) — even if past reactions have been mild. Learn how to recognize a severe allergic reaction and know what to do if one occurs. You may need to carry an emergency epinephrine shot (EpiPen, Twinject) for emergency self-treatment.

If you have a food intolerance, your doctor may recommend steps to aid digestion of certain foods or to treat the underlying condition causing your reaction.