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.
An "allergen" is a substance that causes a food allergy. The majority of allergens are harmless, that is, most people are not affected by them.
The National Institute of Allergy and Infectious Diseases1 estimates that about 5% of children and 4% of adults in the USA have a food allergy.
However, according to a study carried out at Johns Hopkins Children's Center and the National Institutes of Health and published in the Journal of Allergy2, approximately 2.5% of Americans are believed to have at least one food allergy.
According to Allergy UK3, hospital admissions for food allergies have increased by 500% since 1990.
A higher percentage of children have food allergies than adults, because their immune systems are not yet fully developed.
A study carried out at the Northwestern University Feinberg School of Medicine published in JAMA Pediatrics4 (September 2013 issue) reported that kids' food allergies cost both families and the US as a whole almost $25 billion annually - approximately $4,184 per child.
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.
Contents of this article:
Common foods to trigger allergic reactions
According to the National Health Service5, UK, 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.
The most common allergenic foods, which account for about 90% of all food allergies, commonly referred to as the 'big eight', are:
- nuts from trees (including hazelnuts, walnuts, almonds, and Brazil nuts)
- peanuts (groundnuts)
- shellfish (including shrimps, mussels, and crab)
A summary of these common food allergies is available here.
Allergy and intolerance
Experts have found that many people who think they have a food allergy have food intolerance, which is not the same.
Food intolerance does not 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.
What causes food allergies?
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.
American researchers carried out a study which found that tap water is likely responsible for the increase in food allergies in the United States. Elina Jerschow, M.D., M.Sc., reported in the journal Annals of Allergy, Asthma and Immunology6 that high levels of dichlorophenols, a chemical used to chlorinate water and also used in pesticides, is associated with food allergies when found in a patient's body.
Dr. Jerschow wrote "Our research shows that high levels of dichlorophenol-containing pesticides can possibly weaken food tolerance in some people, causing food allergy. This chemical is commonly found in pesticides used by farmers and consumer insect and weed control products, as well as tap water."
Signs and symptoms
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
- 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
- Respiratory problems, which often become progressively worse
- Skin is itchy. A rash may spread rapidly and cover much of the body
- Streaming nose and eyes
- Tachycardia (accelerated heartbeat)
- The throat, lips, face and mouth swell rapidly
- The patient may lose consciousness.
Why do certain people have allergic reactions?
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 others 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.
Tests and diagnosis
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. However, many doctors consider IgG4 testing as inadequate for diagnosing food allergies.
Dr. Elana Lavine, at Humber River Regional Hospital in Toronto wrote in CMAJ (Canadian Medical Association Journal)7 "Physicians should caution patients about the controversy surrounding testing for food sensitivity. Recent position papers from European and American allergy and immunology societies have emphasized the limitations and potential misuse of IgG4 testing, indicating that these tests are not appropriate for making a diagnosis of food allergy."
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.
Standard test for milk allergies may be unreliable - a study8 done at the University of Nebraska-Lincoln found that the standard test to detect milk-protein residues in processed foods may not be as reliable as previously believed.
The test may sometimes miss ingredients that cause milk allergies, lead researcher Joseph L. Baumert, Ph.D., explained at the 243rd National Meeting & Exposition of the American Chemical Society.
Dr. Baumert explained that thermal and non-thermal food processing procedures can alter the proteins that cause milk allergies in ways that make them harder to detect using the enzyme-linked immunosorbent assay (ELISA), the standard test.
Baumert wrote "The results of these studies could be utilized by commercial ELISA kit manufacturers to aid in improving ELISAs for detection of milk residue in processed food products. These improved tests can be adopted by the food industry, if necessary, to allow for reliable detection of milk residue regardless of the type of processing that is used. These improvements should not result in commercial tests that are more expensive or difficult for food processors to use."
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.
Researchers at National Jewish Health in Denver, Colorado, found that too many children are needlessly avoiding foods based on incomplete data regarding potential food allergies.
David Fleischer, MD, and colleagues carried out a retrospective chart review of 125 kids who had been evaluated for suspected food allergies. Between 84% and 93% of foods being avoided were eventually restored to their diets after an oral food challenge.
Dr. David Fleischer said "People with known food allergies, especially those with a history of anaphylactic reactions, should by all means avoid those foods. However, a growing number of patients referred to our practice are being placed on strict, unproven food-elimination diets that have led to poor weight gain and malnutrition. These overly restrictive diets have been chosen for a variety of reasons, but overreliance on immunoassay tests appears to be the most common cause."
Recent developments on food allergies from MNT news
Food allergies are growing in prevalence in developed countries, and 3% of children globally are allergic to cow's milk. New research carried out on children with cow's milk allergy has shown that structural differences in gut bacteria may be the reason why some children do not acquire tolerance.
A new review published in CMAJ, the Canadian Medical Association Journall, provides guidance for physicians and families on how they should introduce foods to infants in order to decrease allergy risks.
Medication 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.
Epinephrine (adrenaline) - this is used for more severe cases, such as anaphylaxis. Epinephrine 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.
People who have had severe allergic reactions should carry an epinephrine autoinjector with them, which may include the EpiPen, EpiPen Jr, Twinject, or Anapen.
Quality of life
People with food allergies live in a state of uncertainty, says Dr Anthony Dubois of the Beatrix Children's Hospital in The Netherlands.
Dr. Dubois concluded after using a psychological test to measure HRQL (health-related quality of life) that the perceived quality of life for people with food allergy is worse than those with diabetes.