FOR most people, eating is a pleasant experience. There are some, however, who are compelled to treat certain foods as “enemies.” Like Emily, quoted earlier, they suffer from food allergies. Emily’s severe allergic response is called anaphylaxis, a very dangerous condition. Thankfully, most food allergies are not as serious.

In recent years, there has been a rise in reported food allergies and intolerances. Some studies, however, suggest that only a small portion of those who think they have a food allergy have been definitely diagnosed.

“Food allergy has no universally accepted definition,” according to a group of scientists led by Dr. Jennifer J. Schneider Chafen in their report published in The Journal of the American Medical Association. However, most experts believe that allergic reactions are primarily triggered by the immune system.

An allergic reaction to a certain food is typically a response to a protein in that food. The immune system erroneously identifies that protein as harmful. When a particular protein enters the body, the immune system may create a type of antibody known as IgE to neutralize the perceived invader. When the food allergen is again ingested, the antibodies that were created earlier can trigger a release of chemicals, including histamine.

Under normal circumstances, histamine plays a beneficial role in the immune system. But for reasons not clearly understood, the presence of IgE antibodies and the subsequent release of histamine provoke an allergic reaction in people who happen to be hypersensitive to a particular food protein.

This explains why you could eat a new food without any apparent reaction but eat the same food again and experience an allergic reaction.

A food intolerance, like a food allergy, may be an adverse reaction to a food item. But unlike a food allergy (which is triggered directly by the immune system), a food intolerance is a reaction of the digestive system, and thus no antibodies are involved. Basically, a person may have trouble breaking down a food, perhaps because of enzyme deficiencies or because of  chemicals found in the food that are difficult to process. For example, a lactose intolerance occurs when the gut does not produce the needed enzymes to digest the type of sugars found in milk products.

As it is not a matter of the production of antibodies, a food intolerance can manifest itself the first time the food is ingested. Quantity may be the determining factor​—a small amount of a certain food may be tolerated, but a problem may occur when larger amounts are ingested. This is different from severe food allergies in which even a tiny amount of food can cause a life-threatening reaction.

If you suffer from a food allergy, you could have itching; hives; swelling of the throat, eyes, or tongue; nausea; vomiting; or diarrhea. And in a worst-case scenario, you could have a drop in blood pressure, dizziness, fainting, and even cardiac arrest. An anaphylactic reaction can progress rapidly and be fatal.

Potentially, any food could cause an allergy. However, the most severe food allergies are commonly caused by just a few foods: namely, milk, eggs, fish, crustaceans, peanuts, soybeans, tree nuts, and wheat. A person can develop an allergy at any age. Studies show that genetics play an important role, and a child is more likely to develop an allergy if one or both of his parents have allergies. It is not uncommon for children to grow out of allergies.

Symptoms of food intolerance are generally less alarming than those of extreme allergic reactions. Food intolerance may cause stomach pain, bloating, gas, cramps, headaches, skin rash, tiredness, or a general feeling of malaise. An intolerance may be related to a variety of foods​—dairy, wheat, gluten, alcohol, and yeast are among the most common.

If you think you may suffer from a food allergy or a food intolerance, you may decide to get checked by a specialized health professional. Self-diagnosis and autonomously deciding to eliminate certain foods can at times be harmful, as you may inadvertently deprive your body of necessary nutrients.

There is no widely accepted treatment for severe food allergies other than the total avoidance of the particular foods that trigger the allergy. a On the other hand, if you have milder food allergies or food intolerance, you may see some benefit from simply reducing how often you eat certain foods and the amount. In some cases, however, sufferers are compelled to avoid the foods in question altogether, or at least for some time, depending on the severity of the intolerance.

So if you have a food allergy or a food intolerance, you may find comfort in knowing that many sufferers have learned to manage their condition and still enjoy a wide variety of nutritious and delicious foods.