A food allergy is a condition in which certain foods trigger an abnormal immune response (2).
It's caused by your immune system wrongly recognizing some of the proteins in a food as harmful. Your body then launches a range of protective measures, including releasing chemicals like histamine, which causes inflammation.
For people who have a food allergy, even exposure to very small amounts of the problem food can cause an allergic reaction.
Symptoms can occur anywhere from a few minutes after exposure to a few hours later, and they may include some of the following:
Swelling of the tongue, mouth or face
Difficulty breathing
Low blood pressure
Vomiting
Diarrhea
Hives
Itchy rash
In more severe cases, a food allergy can cause anaphylaxis. Symptoms, which can come on very quickly, include an itchy rash, swelling of the throat or tongue, shortness of breath and low blood pressure. Some cases can be fatal (3).
Many food intolerances are often mistaken for food allergies.
However, food intolerances never involve the immune system. This means that while they can severely impact your quality of life, they are not life threatening.
True food allergies can be divided into two main types: IgE antibody or non-IgE antibody. Antibodies are a type of blood protein used by your immune system to recognize and fight infection (4).
In an IgE food allergy, the IgE antibody is released by your immune system. In a non-IgE food allergy, IgE antibodies aren't released, and other parts of the immune system are used to fight the perceived threat.
Here are the eight most common food allergies.
1. Cow's Milk
An allergy to cow's milk is most often seen in babies and young children, especially when they have been exposed to cow's milk protein before they are six months old (5, 6).
It's one of the most common childhood allergies, affecting 2–3% of babies and toddlers (7).
However, around 90% of children will outgrow the condition by the time they're three, making it much less common in adults.
A cow's milk allergy can occur in both IgE and non-IgE forms, but IgE cow milk allergies are the most common and potentially the most serious.
Children or adults with an IgE allergy tend to have a reaction within 5–30 minutes of ingesting cow's milk. They experience symptoms like swelling, rashes, hives, vomiting and, in rare cases, anaphylaxis.
A non-IgE allergy usually has more gut-based symptoms like vomiting, constipation or diarrhea, as well as inflammation of the gut wall (6).
A non-IgE milk allergy can be quite difficult to diagnose. This is because sometimes the symptoms can suggest an intolerance and there is no blood test for it (8).
If a diagnosis of a cow's milk allergy is made, the only treatment is to avoid cow's milk and foods that contain it. This includes any foods or drinks that contain:
Milk
Milk powder
Cheese
Butter
Margarine
Yogurt
Cream
Ice cream
Breastfeeding mothers of babies with an allergy may also have to remove cow's milk and foods that contain it from their own diets.
As for babies who aren't breastfeeding, a suitable alternative to a cow's milk-based formula will be recommended by a health professional (9).
Summary:
A cow's milk allergy mostly affects children under the age of three. A diagnosis of cow's milk allergy means that all milk and milk products must be avoided.
2. Eggs
An egg allergy is the second most common cause of food allergy in children (10, 11).
However, 68% of children who are allergic to eggs will outgrow their allergy by the time they're 16 (12).
Symptoms include:
Digestive distress, such as a stomach ache
Skin reactions, such as hives or a rash
Respiratory problems
Anaphylaxis (which is rare)
Interestingly, it's possible to be allergic to egg whites, but not the yolks, and vice versa. This is because the proteins in egg whites and egg yolks differ slightly.
Yet most of the proteins that trigger an allergy are found in egg whites, so an egg white allergy is more common (11).
Like other allergies, the treatment for an egg allergy is an egg-free diet (13).
However, you may not have to avoid all egg-related foods, as heating eggs can change the shape of the allergy-causing proteins. This can stop your body from seeing them as harmful, meaning they're less likely to cause a reaction (14, 15, 16).
In fact, one study found that around 70% of children with an egg allergy could tolerate eating biscuits or cakes containing a cooked egg component (17).
Some studies have also shown that introducing baked goods to children with an egg allergy can shorten the time it takes for them to outgrow the condition (18).
Nevertheless, this isn't the case for everybody, and the consequences of ingesting eggs when you are allergic to them can be severe. Because of this, you should check with your doctor before you reintroduce any egg-containing foods.
Summary:
The most common type of egg allergy is an egg white allergy. The treatment is an egg-free diet. However, some people may be able to reintroduce some foods containing cooked eggs into their diet.
3. Tree Nuts
A tree nut allergy is an allergy to some of the nuts and seeds that come from trees.
It's a very common food allergy that's thought to affect around 1% of the US population (19, 20, 21).
Some examples of tree nuts include:
Brazil nuts
Almonds
Cashews
Macadamia nuts
Pistachios
Pine nuts
Walnuts
People with a tree nut allergy will also be allergic to food products made with these nuts, such as nut butters and oils.
They are advised to avoid all types of tree nuts, even if they are only allergic to one or two types (22).
This is because being allergic to one type of tree nut increases your risk of developing an allergy to other types of tree nuts.
Additionally, it's easier to avoid all nuts, rather than just one or two types. And unlike some other allergies, an allergy to tree nuts is usually a lifelong condition.
Allergies can also be very severe, and tree nut allergies are responsible for around 50% of anaphylaxis-related deaths (23, 24).
Because of this, people with nut allergies (as well other potentially life-threatening allergies) are advised to carry an epi-pen with them at all times.
An epi-pen is a potentially life-saving device that allows those with allergies to inject themselves with a shot of adrenaline if they begin to have a severe allergic reaction.
Adrenaline is a naturally occurring hormone that stimulates the body's "fight or flight" response when you are stressed.
When given as an injection to people having a severe allergic reaction, it can reverse the effects of the allergy and save the person's life (25).
Summary:
A tree nut allergy is one of the most common food allergies. It's frequently associated with severe allergic reactions, and the treatment is usually a lifelong avoidance of all tree nuts and tree nut products.
4. Peanuts
Like a tree nut allergy, peanut allergies are very common and can cause severe and potentially fatal allergic reactions.
However, the two conditions are considered distinct, as a peanut is a legume. Nevertheless, those with peanut allergies are often also allergic to tree nuts.
While the reason people develop a peanut allergy isn't known, it is thought that people with a family history of peanut allergies are most at risk.
Because of this, it was previously thought that introducing peanuts through a breastfeeding mother's diet or during weaning may trigger a peanut allergy.
However, studies have since shown that introducing peanuts early may be protective (26).
Peanut allergies affect around 4–8% of children and 1–2% of adults (27, 28).
However, around 15–22% of children who develop a peanut allergy will find it resolves as they move into their teenage years.
Like other allergies, a peanut allergy is diagnosed using a combination of patient history, skin prick testing, blood tests and food challenges.
At the moment, the only effective treatment is complete avoidance of peanuts and peanut-containing products (22).
However, new treatments are being developed for children with peanut allergies. These involve giving precise and small amounts of peanuts under strict medical supervision in an attempt to desensitize them to the allergy (29, 30).
Summary:
A peanut allergy is a serious condition that can cause a severe allergic reaction. Treatment is lifelong avoidance of peanuts and peanut-containing products.
5. Shellfish
A shellfish allergy is caused by your body attacking proteins from the crustacean and mollusk families of fish, which are known as shellfish.
Examples of shellfish include:
Shrimp
Prawns
Crayfish
Lobster
Squid
Scallops
The most common trigger of a seafood allergy is a protein called tropomyosin. Other proteins that may play a role in triggering an immune response are arginine kinase and myosin light chain (31, 32).
Symptoms of a shellfish allergy usually come on quickly and are similar to other IgE food allergies.
However, a true seafood allergy can sometimes be hard to distinguish from an adverse reaction to a contaminant of seafood, such as bacteria, viruses or parasites.
This is because the symptoms can be similar, as both can cause digestive issues like vomiting, diarrhea and stomach pain.
A shellfish allergy doesn't tend to resolve over time, so most people with the condition must exclude all shellfish from their diet to avoid having an allergic reaction (33).
Interestingly, even the vapors from cooking shellfish can trigger a shellfish allergy in those who are allergic. This means that many people are also advised to avoid being around seafood when it's being cooked (34).
Summary:
The most common trigger of a shellfish allergy is a protein called tropomyosin. The only treatment for a shellfish allergy is removing all shellfish from your diet.
6. Wheat
A wheat allergy is an allergic response to one of the proteins found in wheat.
It tends to affect children the most. Although, children with a wheat allergy often outgrow it by the time they reach 10 years of age (35).
Like other allergies, a wheat allergy can result in digestive distress, hives, vomiting, rashes, swelling and, in severe cases, anaphylaxis.
It is often confused with celiac disease and non-celiac gluten sensitivity, which can have similar digestive symptoms.
However, a true wheat allergy causes an immune response to one of the hundreds of proteins found in wheat. This reaction can be severe and sometimes even fatal (36).
On the other hand, celiac disease and non-celiac gluten sensitivity are not life threatening. They are caused by an abnormal immune reaction to one specific protein — gluten — that also happens to be found in wheat (37).
People with celiac disease or non-celiac gluten sensitivity have to avoid wheat and other grains that contain the protein gluten.
People with a wheat allergy only need to avoid wheat and can tolerate gluten from grains that don't contain wheat.
A wheat allergy is often diagnosed through skin prick testing.
The only treatment is to avoid wheat and wheat-containing products. This means avoiding foods, as well as beauty and cosmetic products, that contain wheat.
Summary:
A wheat allergy can be caused by a sensitivity to any of the hundreds of proteins in wheat. The only treatment is a wheat-free diet, but many people outgrow it before they reach school age.
7. Soy
Soy allergies affect around 0.4% of children and are most commonly seen in infants and children under three (38).
They are triggered by a protein in soybeans or soybean-containing products. However, around 70% of children who are allergic to soy outgrow the allergy.
The symptoms can range from an itchy, tingly mouth and runny nose to a rash and asthma or breathing difficulties. In rare cases, a soy allergy can also cause anaphylaxis (39).
Interestingly, a small number of babies who are allergic to cow's milk are also allergic to soy (40).
Common food triggers of soy allergy include soybeans and soy products like soy milk or soy sauce. Since soy is found in many foods, it's important to read food labels.
Like other allergies, the only treatment for soy allergy is the avoidance of soy.
Summary:
A soy allergy is triggered by the proteins in soybeans and soybean products. If you have a soy allergy, the only treatment is the removal of soy from your diet.
8. Fish
Fish allergies are common, affecting up to around 2% of adults (41).
Unlike other allergies, it's not uncommon for a fish allergy to surface later in life, with 40% of people developing the allergy as an adult (42).
Like a shellfish allergy, a fish allergy can cause a serious and potentially fatal allergic reaction. The main symptoms are vomiting and diarrhea, but, in rare cases, anaphylaxis can also occur.
This means that those who are allergic to fish are usually given an epi-pen to carry in case they accidentally eat fish.
Because the symptoms can be similar, a fish allergy is sometimes confused for a reaction to a contaminant in fish, such as bacteria, viruses or toxins (43, 44, 45).
What's more, since shellfish and fish with fins don't carry the same proteins, people who are allergic to shellfish may not be allergic to fish.
However, many people with a fish allergy are allergic to one or more types of fish.
Summary:
Fish allergies are common, but they may be confused with an adverse reaction to contaminated fish.
Other Foods
The 8 food allergies outlined above are the most common ones.
However, there are many more.
Less common food allergies can cause an array of symptoms, ranging from mild itching of the lips and mouth (known as oral allergy syndrome) to life-threatening anaphylaxis.
Some less common food allergies include:
Linseed
Sesame seed
Peach
Banana
Avocado
Kiwi fruit
Passion fruit
Celery
Garlic
Mustard seeds
Aniseed
Chamomile
Summary:
Any food can cause an allergy. Other foods people are allergic to include fruits, vegetables and seeds like linseed or sesame seed.
Think You Have a Food Allergy?
Sometimes it can be difficult to tell food allergies and food intolerances apart.
If you suspect you have a food allergy, it's important to speak to your doctor.
To find out whether you have an allergy or an intolerance, your doctor will probably carry out a number of diagnostic tests (46, 47).
These include:
Dietary review: A detailed review of foods eaten, including timing and symptoms.
Skin prick testing: A small amount of food is "pricked" into the skin using a tiny needle. The skin is then monitored for a reaction.
Oral food challenges: The problem food is eaten in a controlled environment under medical supervision in gradually increasing amounts.
Blood tests: In some circumstances, blood will be drawn and the level of IgE antibodies measured.
If you are allergic to a food, your doctor will advise you on how to manage it. Your doctor may also refer you to a registered dietitian to help with managing your diet.
Summary:
If you suspect you have a food allergy, speak with your doctor. They will diagnose the condition through a number of tests.
The Bottom Line
Most food allergies are caused by eight foods: cow's milk, eggs, tree nuts, peanuts, shellfish, fish, soy and wheat.
Unlike food intolerances, food allergies are caused by your immune system incorrectly identifying some of the proteins in food as harmful.
This can cause potentially life-threatening reactions, and the only treatment is the removal of the food from your diet.
If you suspect you have a food allergy, speak with your doctor about it.
