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. It is the immune system's reaction to these proteins that causes an allergic reaction.
Among children, most allergic reactions to food are caused by peanuts, milk, soybean, tree nuts, 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.
The most common allergenic foods, also known as the 'big eight,' are:
The eight most common food allergies
We look at each of these allergenic foods in turn:
Three proteins cause egg allergy:
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 eat 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.
This is because the allergens in these fish are quite similar. Cooking doesn't destroy fish allergens. In fact, some people with a fish allergy can be allergic to cooked but not raw fish.
Allergy to cows' milk is the most common food allergy in childhood. A reaction can be triggered by small amounts of milk, either passed to the baby through the mother's breast milk from dairy products she has eaten, or from feeding cows' milk to the baby.
Children usually grow out of milk allergy by but about one-fifth of children who have an allergy to cows' milk will still be allergic to it as adults.
Milk allergy symptoms
The symptoms of milk allergy are often mild and can affect any part of the body. They can include:
- stomach cramps
In very few cases, milk allergy can cause anaphylaxis.
Allergy to nuts from trees is usually lifelong. The nuts that are most likely to cause allergic reactions are:
- Brazil nuts
- pine nuts
- macadamia nuts
- cashew nuts
On rare occasions, all these nuts can cause anaphylaxis in people who are sensitive. Sometimes, people with an allergy to one type of nut will also react to other nuts. People with nut allergies should talk to their doctor for advice.
Allergy to peanuts (also known as groundnuts and monkey nuts) is often lifelong.
Peanuts are one of the most common causes of food allergy and can cause severe reactions, including anaphylaxis. They contain allergens that are not destroyed by cooking or roasting.
Peanut allergy can be so severe that very tiny amounts can cause a reaction. Because of this, coming into contact with traces of peanut can be enough to cause a reaction in people who are sensitive.
Refined peanut oil is thought to be safe for people with peanut allergy, because the proteins that cause allergic reactions are removed during the manufacturing process. However, cold-pressed, or unrefined peanut oil can contain small amounts of peanut allergens, which can cause a reaction in people who are sensitive.
Some people with peanut allergy might also react to other legumes such as:
- green beans
- kidney beans
- green peas
Even though, strictly speaking, peanuts aren't nuts, people with peanut allergy are sometimes allergic to nuts from trees such as almonds, walnuts, hazelnuts, Brazil nuts, and cashew nuts.
Allergy to shellfish is quite common. Many different types of shellfish can cause reactions in people who are sensitive, including:
People who are allergic to one type of shellfish often find that they react to other types. Shellfish allergy can often cause severe reactions, and some people can even react to the vapors from cooking shellfish.
Soybean allergy is a common childhood allergy. Most people grow out of it by the age of two, but occasionally adults are allergic to soybean. The symptoms of soybean allergy are similar to milk allergy, and they include:
- stomach cramps
Some people with soybean allergy might also react to milk. Very rarely, soybean can cause anaphylaxis.
Soybean is used as an ingredient in about two-thirds of all manufactured food products, including bakery goods, sweets, drinks, breakfast cereals, ice cream, margarine, pasta, processed meats, and seasoned foods.
Wheat allergy is common, particularly among babies. One of the main allergens in wheat is a protein called gliadin, which is found in gluten. Because of this, people with a wheat allergy are sometimes recommended to eat a gluten-free diet.
As with all food allergies, people who suspect they may be allergic will need to speak with their doctor before altering their diet.
Other common food allergies
People can be allergic to almost any food. As a result, there are many allergies that affect a lot of people but aren't part of the big eight; these include:
- Cereal allergy - the most common foods in this category are oats, wheat, maize (corn), rice, rye, and barley.
- Coconut allergy - uncommon, though patients may experience anaphylaxis. Those with other nut allergies are more likely to be allergic to coconut.
- Fruit and vegetable allergy - allergic reactions to fruits and vegetables are usually mild. Cooking vegetables often destroys the allergens.
- Pine nut allergy - pine nuts can cause severe allergic reactions, including anaphylaxis. People who are allergic to pine nuts might also react to peanuts and nuts, such as almonds.
- Meat allergy - people with a meat allergy might react to beef, mutton, pork, or chicken. Cooking destroys some of the allergens in meat, but some people will still react.
- Quorn allergy - Quorn is a type of protein, which is made from a fungus. There have been some reports of intolerance to Quorn, but this is not surprising because allergens are usually proteins.
- Rice allergy - people who are allergic to rice can react when they eat it or when they inhale its pollen.
- Sesame allergy - sesame allergy is increasing, possibly because it's now more commonly used. Sesame seeds, sesame oil, and other sesame products, such as tahini, can cause anaphylaxis.
- Spice allergy - reactions to spices are usually mild, but severe reactions can happen occasionally. Some people react to mustard, coriander, caraway, fennel, paprika, or saffron.
Food allergies may progress or get better over time. Anyone suspecting they are allergic to a food should consult their doctor for advice.