What Is Food Allergy? What To Do When a Food Allergy Is Suspected?

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Main Category: Allergy
Also Included In: Nutrition / Diet
Article Date: 16 Mar 2011 - 0:00 PDT

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People with a food allergy have an immune system which reacts to certain proteins found in food. Their immune system attacks the specific protein as if it were a harmful pathogen, such as a bacterium or virus.

According to various surveys, approximately 20% of adults think they have a food allergy. However, after an evaluation has been carried out by a health care professional, the incidence really is about 1% to 2%. The Food Standards Agency (FSA), UK, reports that about 5% to 8% of children and 1% to 2% of adults have a food allergy. Some research centers estimate the figure for adults is more likely to be around 3% to 4%.

A higher percentage of children have food allergies than adults, because their immune systems are not yet fully developed.

Signs and symptoms can vary and the patient may experience just a tingling in the mouth, or come out with a severe rash and have serious breathing difficulties. When an allergic reaction is severe and life-threatening, it is known as anaphylaxis.

According to the National Health Service (NHS), UK, eight food types account for 90% of all food allergies. Among children the most common foods to trigger allergic reactions are peanuts, wheat, soya, milk, and eggs. In adults they are types of fish, peanuts, some shellfish, such as lobster, crab and prawns, tree nuts, such as pistachios, brazil nuts, almonds and walnuts, and peanuts. A summary of these common food allergies is available here.

Experts say the number of people who think they have a food allergy is much higher than it actually is because a considerable number of individuals mistake food intolerance for a food allergy.

What is the difference between Food Allergy and Food Intolerance?

Food intolerance does not usually involve the immune system. The individual can typically eat small amounts of that particular food without being affected. The following conditions or examples of food intolerance are often confused for food allergies:

• The individual does not have an enzyme (or enough of it) to digest a food properly. For example, lactose intolerance, which causes diarrhea, gas, cramping and bloating.
• IBS (irritable bowel syndrome), a long-term (chronic) condition in which the patient has diarrhea, constipation and stomach pains.
• Food additive sensitivity, such as sulfites which are used for preserving dried fruits or canned foods.
• Psychological factors - some people may feel ill when just thinking about a particular food. Nobody is quite sure why this happens.
• Celiac disease, a long-term digestive condition which is caused by the consumption of gluten. The patient has diarrhea, stomach pains and bloating. There is some immune system involvement, but experts say it is more a food intolerance than an allergy because there is a complex food reaction.

Food allergy means even small amounts of that food is likely to trigger the immune system, an allergic reaction. A food allergy may cause fainting, vertigo, dizziness, respiratory problems, swelling of various parts of the body, such as the throat, tongue, face. The individuals may have tingling in the mouth, as well as hives.

With a food allergy the person's immune system treats a specific protein in a food as a harmful substance, a pathogen, something that may cause disease. It responds by producing antibodies to attack this protein. When that same food is eaten again, the antibodies are there and will tell the immune system to react immediately. The immune system reacts by releasing histamine and other substances into the bloodstream. Histamine and these other chemicals in the bloodstream cause food allergy signs and symptoms.

Histamine causes blood vessels to dilate (expand) and the skin to become inflamed (swollen). It also affects the nerves, making the person feel itchy. The nose may produce more mucous, resulting in itching, burning and a streaming nose. In the majority of allergic reactions, histamine is released to some parts of the body.

Commons signs and symptoms of a food allergy include:

• Tingling in the mouth
• Burning sensation in the lips and mouth
• The lips and face might swell
• A skin rash. The skin may also become itchy and/or blotchy
• Wheezing
• Nausea
• Diarrhea
• Runny nose
• Streaming eyes

Anaphylaxis means a severe allergic reaction. It usually occurs soon after exposure to the specific protein, but can take a few hours. Signs and symptoms usually come on quickly and worsen rapidly, and may include:

• A rapid fall in blood pressure
• Abrupt fear, a feeling of apprehension
• An itchy, tickly throat
• Nausea
• Respiratory problems, which often become progressively worse
• Skin is itchy. A rash may spread rapidly and cover much of the body
• Sneezing
• Streaming nose and eyes
• Tachycardia (accelerated heartbeat)
• The throat, lips, face and mouth swell rapidly
• Vomiting
• The patient may lose consciousness

Why do some people have allergic reactions and others don't?

Family history - people who have a parent or sibling with a peanut allergy have a 7 times higher risk of having that allergy themselves compared to those with no family history, experts say. Scientists believe food allergies could be caused by some genes people inherit.

Other allergies - those who suffer from asthma, atopic dermatitis have a considerably higher risk of developing a food allergy than people with no other allergies.

In the UK, the number of kids hospitalized for food-related anaphylaxis has gone up by over 700% since 1990 - nobody knows why. Some people suggest changes in eating habits in western nations may be the cause, while other say it could be due to a lower consumption of animal fats and higher intake of vegetable fats. Most people eat less fresh fruit and vegetables than those of previous generations - foods high in antioxidants which help protect against cell damage - perhaps a lower antioxidant intake during childhood undermines proper immune system development.

Vitamin D - food allergy prevalence is higher in countries further from the equator, where there is less sunlight, an important source of vitamin D. The suggestion is that low vitamin D intake may result in a higher food allergy risk.

However, all these are currently just theories, with no compelling evidence to support them.

Lack of early exposure - also known as the hygiene hypothesis. Children are being brought up in super-sterile environments, with much lower exposure to germs than their parents were. Perhaps the immune system has not been exposed enough to properly differentiate between good and harmful substances. This hypothesis does not only apply to food allergies, but most others as well.

How is a food allergy diagnosed?

The doctor will ask the patient about their reaction in order to possibly rule out a food allergy. This can often be ascertained if the physician is told about the symptoms, how long it takes for a reaction to occur, which foods cause it, whether the food is cooked or not, and where it was eaten. The doctor will be interested in any other existing allergies, such as hay fever or asthma. The patient will also need to tell the doctor about close relatives who might have allergies.

Skin prick test - diluted foods are placed on the patient's arm, and then the skin is pierced, introducing the food into the system. If there is any reaction, such as itching, swelling or redness, it is likely there is some kind of allergy. Skin prick testing can sometimes produce false-negative or false-positive results. Doctors usually order other tests to be sure.

Blood test - the patient is exposed to tiny quantities of foods believed to cause an allergic reaction and subsequently checking for IgE antibodies. Even here, there is a high risk of false-negative results.

Exclusion diet - suspected foods are not eaten for a while to see whether symptoms clear up. They are then reintroduced to determine whether they come back. The NHS, UK, says exclusion diets should be done with a qualified health care professional or dietitian. You should not exclude huge classes of foods.

Food diary - patients write down everything they eat, and describe symptoms, if there are any.

Blinded challenge testing - this is more accurate. The patient is given several different foods. One of them has tiny amounts of the suspected allergen. The patient eats each one and his/her reaction is observed closely. Blinded means the patient does not know which food has the suspected allergen, because some people react psychologically to some foods (which would not be an allergy). This type of test should only be done with a health care professional at a suitable medical facility.

What are the treatment options for a food allergy?

Elimination diet - many patients will need to see a dietitian after being diagnosed with a food allergy. It is important if food needs to be eliminated from one's diet, that is done in a way that does not undermine the individual's health.

If your allergy is just to peanuts, there will be no health consequences if you never touch peanuts again. However, an allergy to milk means seeking out other important sources of calcium.

Elimination does not only mean not eating the offending substance or food, it also includes never inhaling it, touching it or eating foods with traces of it inside. Cutlery, crockery, cooking surfaces and chopping boards must be free of the allergen.

Patients will need to read food and/or drink labels carefully.

Even some soaps, pet foods, glues and adhesives may have traces of a food allergen.

When eating out you may need to be especially careful.

Medications for emergencies

Antihistamines - these will come in the form of gels or tablets. They are usually effective for patients with mild or moderate allergies. Histamines are proteins which cause most allergy symptoms, antihistamines block their effects.

Adrenaline - this is used for more severe cases, such as anaphylaxis. Adrenaline keeps your blood pressure up by constricting the blood vessels, as well as easing the airways. The patient will probably be given an auto-injector pen.

Written by Christian Nordqvist
Copyright: Medical News Today
Not to be reproduced without permission of Medical News Today

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