The most common foods that cause allergic reactions are milk, shellfish, peanuts, tree nuts, fish and eggs. (Jeffrey Mark Reese/The Daily Campus)

Food allergies are often self-diagnosed by people around the world who have experienced abnormal responses to food. Most of the time, however, this perception is classified as food intolerance rather than an allergy. A food allergy is not common but it can be serious. It can be caused by a variety of foods that respond unpleasantly to the human body and its symptoms vary from mild to harmful and dangerous reactions.

What is the difference between a food allergy and intolerance?

It is common to mistake intolerance with a food allergy as the two often have similar signs and symptoms.

The difference between a clinically proven food allergy and a food intolerance is that a food allergy is much more severe than an intolerance and it can cause a wide range of harmful symptoms. Food intolerances are much more widespread than food allergies. They can occur in a variety of diseases and are triggered by different means from which food allergies are caused. Common types of food intolerances include lactose, food poisoning and toxic reactions.

Food allergies can be severe and even life threatening while food intolerances are primarily limited to digestive problems and have much less critical symptoms. People often think that they have a food allergy when they experience a disagreeable reaction to food, however only about 3 percent of adults and 6 to 8 percent of children have a clinically proven food allergy.

How does the allergy occur?

A food allergy occurs when the immune system perceives a certain protein that a person consumes as dangerous and uses antibodies to attack the protein as if it were a virus or bacteria.

An allergic reaction triggers two different components in the immune system. The first is an allergy antibody called immunoglobulin E, which circulates through the blood. The other component is the mast cell – a type of immune cell that is found in all tissues of the body, but primarily those that are involved in allergic reactions such as the nose, throat, lungs, skin and gastrointestinal tract.

Food allergies tend to be hereditary. Generally, a person who has an allergic reaction to food often comes from a family who has allergies as well, although the family member’s allergies do not necessarily have to be food-related.

Therefore, those that have parents with allergies are much more likely to develop them than those that do not.

Before an allergic reaction can occur, a person must have already come into contact with the specific food that he or she is allergic to. During this initial encounter with the food, the body’s lymphocytes (a type of white blood cell) produce the immunoglobulin E that is specific for the allergen. The immunoglobulin E is then released and attached to the surface of the mast cells in different tissues of the body.

After this process occurs, the next time that the person eats that same food, the allergens trigger the immunoglobulin E that is attached to the mast cells and causes them to release chemicals – mostly a substance called histamine, which is stored in the mast cells. This reaction creates a variety of symptoms that range from minimal to severe depending on the tissue that the chemicals are released from.

What are the symptoms of a food allergy?

An allergic reaction can happen immediately or it can take up to an hour after eating for symptoms to occur. Some of the first signs of an allergic reaction include a runny nose, itching of the skin or in the mouth, swelling of the tongue or difficulty breathing.

Once the food begins to digest in the stomach, symptoms such as nausea, vomiting, diarrhea and abdominal pain may begin to occur. After the allergens are absorbed and enter the bloodstream they reach the skin, which can cause hives, eczema and asthma.

As the allergens continue to pass through the blood vessels a person can feel lightheaded, weak and a sudden drop in blood pressure that is called anaphylaxis.

Anaphylaxis is the most severe type of allergic response. An anaphylactic reaction can occur when several problems in the body happen all at once, involving the skin, breathing, digestion, the heart and blood vessels. If it is not treated quickly, an anaphylactic reaction can be deadly.

How is the allergy treated?

The most common and effective treatment for a food allergy is dietary avoidance. However when this method isn’t possible certain medicines such as antihistamines are used for mild reactions and an allergy kit, which contains a syringe of epinephrine and antihistamine tablets, is used for serious reactions.

While children can outgrow their food allergies, adults usually do not. It is important for those who have food allergies to notify friends and family of their condition in order to help avoid specific foods. It is also crucial to read all food labels to make sure that they don’t contain any food allergens.