Any food can cause an allergy, theoretically. However, just a handful of foods cause at least 90% of allergic reactions to food.
The substance that causes an allergic reaction in foods or drinks is called an "allergen". As far as foods are concerned, nearly all allergens are proteins. For the majority of people these proteins are not allergens, because their immune system does not react to them.
The most common allergenic foods
The most common allergenic foods, also known as the 'big eight', are:
- nuts from trees (including hazelnuts, walnuts, almonds, and Brazil nuts)
- peanuts (groundnuts)
- shellfish (including shrimps, mussels, and crab)
We look at each of these allergenic foods in turn below.
Among children, most allergic reactions to food are to peanuts, milk, soya, nuts from trees, eggs and wheat. The majority of children stop being allergic to foods early on in their childhood. Allergic adults typically react to citrus fruit, nuts, fish, peanuts, shellfish and wheat.
Pesticides in tap water causing more food allergies
Researchers from the American College of Allergy, Asthma and Immunology found that pesticides in tap water could be causing the recent rise in food allergies. They published their study in the December 2013 issue of Annals of Allergy, Asthma and Immunology.
The scientists explained that chemicals used to chlorinate water as well being added to pesticides - dichlorophenols - are associated with food allergies when found in a person's body.
Elina Jerschow, M.D., M.Sc., said:
"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."
Previous studies have shown that both food allergies and environmental pollution are increasing in the United States. The results of our study suggest these two trends might be linked, and that increased use of pesticides and other chemicals is associated with a higher prevalence of food allergies."
What is the difference between a food intolerance and a food allergy
A food allergy triggers an immune system reaction that affects several organs in the body. Food intolerance symptoms are less severe and affect only the digestive system. In fact, experts say that many people who believe they have a food allergy have some kind of food intolerance.
You can read more about food intolerance here and for a more detailed explanation of the above, see our article explaining the differences between a food intolerance and a food allergy.
Cereal allergies can affect both children and adults. The most common foods in this category are oats, wheat, maize (corn), rice, rye and barley.
Some patients may be allergic to more than one type of cereal.
Coconut allergy is uncommon. Affected patients can have serious reactions, including anaphylaxis, which can be dangerous.
People with nut allergies and/or latex allergies are more likely to be allergic to coconut.
Gluten can be found in barley, rye, wheat oats and some other cereals. It consists of a mixture of proteins.
Celiac disease (gluten intolerance) is a chronic disease, which can eventually damage the lining of the small intestine, affecting the bodys ability to properly absorb nutrients, causing diarrhea and eventually malnutrition. Celiac disease may be hereditary, it can sometimes run in families, but experts are not sure what causes it.
Celiac disease is said to affect 1 in every 100 people in the US.
According to the Celiac Disease Foundation, approximately 1 percent of people are affected by celiac disease.
If a person has celiac disease, they will typically be diagnosed as infants after weaning, when cereals are added to their diet. However, the disease can emerge later on in life. Some studies have found that holding back on wheat foods until the baby is at least four to six months old may reduce the risk of developing celiac disease.
Celiac disease is also more common among patients with certain neurological disorders, ulcerative colitis, type 1 diabetes, and thyroid problems.
Celiac disease is incurable. Stopping symptoms is simply a question of avoiding gluten-containing foods, including beer and lager, malt flavoring, malt extract, malt, barley, rye, oats and wheat.
Processed foods commonly contain hidden gluten. However, a large number of gluten-free products, such as pasta, cakes and bread are available in some bakeries, specialist shops and supermarkets. Celiac UK, a charity to support people with gluten intolerance, works with manufacturers to produce a regularly updated list of foods that don't contain gluten. Read more about celiac disease.
Egg allergies are more common in childhood.
Like most food allergies, egg allergy is more common in childhood and about half the children who have it will grow out of it by the age of three. In a few cases, egg allergy can cause anaphylaxis.
Egg allergy is mainly caused by three proteins in the egg white called ovomucoid, ovalbumin and conalbumin. Cooking can destroy some of these allergens, but not others. So some people might react to cooked eggs, as well as raw eggs.
Occasionally someone might react to egg because they have an allergy to chicken, quail or turkey meat, or to bird feathers. This is called bird-egg syndrome.
Fish allergy can often cause severe reactions, including anaphylaxis. Adults are more likely to have an allergic reaction to fish and shellfish than children, which is probably because adults will have eaten these foods more often.
People who are allergic to one type of fish, such as cod, often react to other types of fish such as hake, haddock, mackerel and whiting as well. This is because the allergens in these fish are quite similar. Cooking doesn't destroy fish allergens. In fact, some people with fish allergy can be allergic to cooked but not raw fish.
Fruit and vegetable allergy
Allergic reactions to fruits and vegetables are usually mild and often they just affect the mouth, causing itching or a rash where the food touches the lips and mouth. This is called oral allergy syndrome. A number of people who react in this way to fruit or vegetables will also react to tree and weed pollens. So, for example, people who are allergic to birch pollen are also likely to be allergic to apples.
Cooking can destroy a number of the allergens in fruits and vegetables, so cooked fruit often won't cause a reaction in people with an allergy to fruit. Pasteurised fruit juice might not cause an allergic reaction either, for the same reason. However, the allergens in some vegetables, such as celery, aren't affected by cooking. Some fruits and vegetables, such as tomatoes, are more likely to cause a reaction as they get riper.
On the next page we look at more common food allergies and intolerances, including gluten, lactose, maize, meat and milk. On the final page we discuss food allergies such as nuts, Quorn, rice, seafood, soya and more.