Food Allergy vs Food Intolerance: Can You Tell the Difference?

Author: Wang Xueyan, Chief Physician, Beijing Century Altar Hospital, Capital Medical University

Reviewer: Gu Qinglong, Chief Physician, Children's Hospital Affiliated to Capital Institute of Pediatrics

In this era where delicious food is everywhere, we enjoy the pleasure brought by a variety of delicious foods. However, for some people, certain foods are not only a feast for the taste buds but may also become "invisible killers" of health.

Food allergy and food intolerance, these two seemingly similar but very different concepts, often confuse people.

1. Food allergies: Why does the body "overreact" to food?

Food allergy, as the name implies, is an abnormal immune response of the human body to certain foods. This reaction originates from the individual's allergic constitution. When an allergic person is exposed to an allergen for the first time, a sensitization process will occur in the body; when exposed to the same allergen again, under certain environmental conditions, it will trigger an allergic reaction of the immune system. These specific environments may include increased work and life pressure, mood swings, or declining health.

Common foods that are prone to allergies include eggs, milk, soybeans, peanuts, shrimp, crabs, wheat, etc. The reason why these foods have become common allergens is that they contain strong allergenic proteins.

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Symptoms of food allergies vary, the most common of which are digestive tract and skin mucosal reactions, such as numbness in the mouth, itchy throat, discomfort in the tongue, itchy skin, and wheals (urticaria). However, food allergies may affect more organ systems than just these, including the respiratory tract and nervous system.

It is worth noting that food allergies are related to intake and can manifest as either immediate or delayed. Immediate allergies can quickly cause severe symptoms even with a trace amount of allergen, while delayed allergies require a certain amount of intake before they appear. In some extreme cases, simply smelling the allergen can trigger symptoms.

2. Food intolerance: Why can’t the body digest certain foods?

Unlike food allergies, food intolerance does not involve immune mechanisms and is mainly caused by the lack of certain enzymes in the digestive tract. Take milk as an example. If the human body lacks lactase, it cannot break down the lactose in milk into monosaccharides, which causes lactose to accumulate in the intestines, causing symptoms such as bloating, diarrhea, and abdominal pain.

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Symptoms of food intolerances usually develop more slowly and last longer. This is because food intolerances are caused by the body's inability to digest or absorb a certain food component, rather than the immune system viewing the food as harmful.

The clinical manifestations of food intolerance are wide and varied. In addition to common digestive system symptoms such as bloating, diarrhea, and abdominal pain, they may also be accompanied by skin reactions such as rashes and itching, as well as neurological symptoms such as headaches and difficulty concentrating. Long-term intake of intolerant foods may also cause chronic fatigue, mood swings, etc. Therefore, food intolerance does not usually cause severe allergic reactions, but long-term intake of intolerant foods may have adverse effects on health.

3. How to distinguish food allergy from food intolerance?

Although both food allergies and food intolerances are related to food, their mechanisms and symptoms are quite different. Food allergies are caused by an IgE-mediated immune response, which is an immediate allergic reaction with symptoms that may involve multiple systems, while food intolerances are caused by a lack of certain enzymes in the digestive tract, and symptoms usually occur more slowly and are limited to the digestive system.

The best way to distinguish between food allergies and intolerances is to undergo a professional medical examination. Doctors can determine whether a food allergy exists by asking about medical history, performing skin prick tests, or testing the levels of specific antibodies in the serum. For food intolerances, doctors usually advise patients to avoid eating intolerant foods and improve symptoms by adjusting their diet.