What causes food allergies in adults

A food intolerance isn’t the same as a food allergy.

People with food intolerance may own symptoms such as diarrhoea, bloating and stomach cramps. This may be caused by difficulties digesting certain substances, such as lactose. However, no allergic reaction takes place.

Important differences between a food allergy and a food intolerance include:

  1. Immunoglobulin E (IgE) mediated – this is where symptoms result from the body’s immune system making antibodies called IgE.

    This type of food allergy can trigger anaphylaxis, life-threatening allergic reactions. Most of our content on this site relates to IgE mediated food allergy.

  2. the symptoms of a food intolerance generally happen several hours after eating the food
  3. a food intolerance is never life threatening, unlike an allergy
  4. you need to eat a larger quantity of food to trigger an intolerance than an allergy
  5. Non-IgE mediated – this is where other parts of the body’s immune system react, causing symptoms, but does not involve the IgE antibody. Numerous non-IgE reactions are believed to be T-cell mediated.

Read more about food intolerance.

Sheet final reviewed: 15 April 2019
Next review due: 15 April 2022

Food allergy defined

A food allergy occurs when the body’s immune system sees a certain food as harmful and reacts by triggering an allergic reaction.

There are two categories of food allergy:

  • Your immune system normally protects you from germs and disease. It helps you to fight off bacteria, viruses, and other tiny organisms that can make you ill.
  • Immunoglobulin E (IgE) mediated – this is where symptoms result from the body’s immune system making antibodies called IgE. This type of food allergy can trigger anaphylaxis, life-threatening allergic reactions. Most of our content on this site relates to IgE mediated food allergy.
  • If you own a food allergy, your immune system mistakenly treats something in a specific food (most often, the protein) as if it’s dangerous to you.

  • Non-IgE mediated – this is where other parts of the body’s immune system react, causing symptoms, but does not involve the IgE antibody. Numerous non-IgE reactions are believed to be T-cell mediated.
  • Your body reacts to the food (an allergen) by having an allergic reaction.

You can own both IgE mediated food allergy and non-IgE mediated food allergy.

IgE mediated food allergy: causes severe allergic reactions that can be life-threatening

When you own this type of food allergy, you own an IgE-mediated immune response to a protein in a food.

Even eating a extremely little quantity of the food or particles of the food can potentially trigger a life-threatening allergic reaction (anaphylaxis).

What causes food allergies in adults

  1. If you own a food allergy, your immune system mistakenly treats something in a specific food (most often, the protein) as if it’s dangerous to you.
  2. Your immune system normally protects you from germs and disease. It helps you to fight off bacteria, viruses, and other tiny organisms that can make you ill.
  3. Your body reacts to the food (an allergen) by having an allergic reaction.

Non-IgE mediated food allergy

Most symptoms of non-IgE mediated food allergies involve the gastrointestinal/digestive tract.

Symptoms may include vomiting and diarrhea, but are not life-threatening. Symptoms can take longer to develop and may final longer than IgE mediated allergy symptoms.

When an allergic reaction occurs with this type of allergy, epinephrine is generally not needed. In general, the best way to treat these allergies is to stay away from the food that causes the reaction. Examples of non-IgE mediated food allergies are below.

Eosinophilic Esophagitis (EoE)

EoE is a swallowing disorder that affects the esophagus, the tube that leads from the throat to the stomach.

Find out what is EoE

Food Protein-Induced Enterocolitis Syndrome (FPIES)

FPIES is an inflammation involving both the little intestine and the large intestine (colon).

Learn about FPIES


Please note, the content under relates to IgE-mediated food allergy.

You can own both IgE mediated food allergy and non-IgE mediated food allergy.

IgE mediated food allergy: causes severe allergic reactions that can be life-threatening

When you own this type of food allergy, you own an IgE-mediated immune response to a protein in a food. Even eating a extremely little quantity of the food or particles of the food can potentially trigger a life-threatening allergic reaction (anaphylaxis).

  1. If you own a food allergy, your immune system mistakenly treats something in a specific food (most often, the protein) as if it’s dangerous to you.
  2. Your immune system normally protects you from germs and disease. It helps you to fight off bacteria, viruses, and other tiny organisms that can make you ill.
  3. Your body reacts to the food (an allergen) by having an allergic reaction.

Non-IgE mediated food allergy

Most symptoms of non-IgE mediated food allergies involve the gastrointestinal/digestive tract.

What causes food allergies in adults

Symptoms may include vomiting and diarrhea, but are not life-threatening. Symptoms can take longer to develop and may final longer than IgE mediated allergy symptoms.

When an allergic reaction occurs with this type of allergy, epinephrine is generally not needed. In general, the best way to treat these allergies is to stay away from the food that causes the reaction. Examples of non-IgE mediated food allergies are below.

Eosinophilic Esophagitis (EoE)

EoE is a swallowing disorder that affects the esophagus, the tube that leads from the throat to the stomach.

Find out what is EoE

Food Protein-Induced Enterocolitis Syndrome (FPIES)

FPIES is an inflammation involving both the little intestine and the large intestine (colon).

Learn about FPIES


Please note, the content under relates to IgE-mediated food allergy.


What causes food allergies?

Food allergies happen when the immune system – the body’s defence against infection – mistakenly treats proteins found in food as a threat.

As a result, a number of chemicals are released. It’s these chemicals that cause the symptoms of an allergic reaction.

Almost any food can cause an allergic reaction, but there are certain foods that are responsible for most food allergies.

Foods that most commonly cause an allergic reaction are:

  1. shellfish
  2. eggs
  3. fish
  4. milk
  5. tree nuts
  6. peanuts
  7. some fruit and vegetables

Most children that own a food allergy will own experienced eczema during infancy.

The worse the child’s eczema and the earlier it started, the more likely they are to own a food allergy.

It’s still unknown why people develop allergies to food, although they often own other allergic conditions, such as asthma, hay fever and eczema.

Read more information about the causes and risk factors for food allergies.


Treatment

The best way to prevent an allergic reaction is to identify the food that causes the allergy and avoid it.

Research is currently looking at ways to desensitise some food allergens, such as peanuts and milk, but this is not an established treatment in the NHS.

Read more about identifying foods that cause allergies (allergens).

Avoid making any radical changes, such as cutting out dairy products, to your or your child’s diet without first talking to your GP.

What causes food allergies in adults

For some foods, such as milk, you may need to speak to a dietitian before making any changes.

Antihistamines can assist relieve the symptoms of a mild or moderate allergic reaction. A higher dose of antihistamine is often needed to control acute allergic symptoms.

Adrenaline is an effective treatment for more severe allergic symptoms, such as anaphylaxis.

People with a food allergy are often given a device known as an auto-injector pen, which contains doses of adrenaline that can be used in emergencies.

Read more about the treatment of food allergies.


Who’s affected?

Most food allergies affect younger children under the age of 3.

Most children who own food allergies to milk, eggs, soya and wheat in early life will grow out of it by the time they start school.

Peanut and tree nut allergies are generally more endless lasting.

Food allergies that develop during adulthood, or persist into adulthood, are likely to be lifelong allergies.

For reasons that are unclear, rates of food allergies own risen sharply in the final 20 years.

However, deaths from anaphylaxis-related food reactions are now rare.


Anaphylaxis

In the most serious cases, a person has a severe allergic reaction (anaphylaxis), which can be life threatening.

Call 999 if you ponder someone has the symptoms of anaphylaxis, such as:

  1. trouble swallowing or speaking
  2. breathing difficulties
  3. feeling dizzy or faint

Ask for an ambulance and tell the operator you ponder the person is having a severe allergic reaction.


Types of food allergies

Food allergies are divided into 3 types, depending on symptoms and when they occur.

  1. non-IgE-mediated food allergy – these allergic reactions aren’t caused by immunoglobulin E, but by other cells in the immune system.

    This type of allergy is often hard to diagnose as symptoms take much longer to develop (up to several hours).

    What causes food allergies in adults

  2. IgE-mediated food allergy – the most common type, triggered by the immune system producing an antibody called immunoglobulin E (IgE). Symptoms occur a few seconds or minutes after eating. There’s a greater risk of anaphylaxis with this type of allergy.

    What causes food allergies in adults

  3. mixed IgE and non-IgE-mediated food allergies – some people may experience symptoms from both types.

Read more information about the symptoms of a food allergy.

Oral allergy syndrome (pollen-food syndrome)

Some people experience itchiness in their mouth and throat, sometimes with mild swelling, immediately after eating unused fruit or vegetables.

What causes food allergies in adults

This is known as oral allergy syndrome.

Oral allergy syndrome is caused by allergy antibodies mistaking certain proteins in unused fruits, nuts or vegetables for pollen.

Oral allergy syndrome generally doesn’t cause severe symptoms, and it’s possible to deactivate the allergens by thoroughly cooking any fruit and vegetables.

The Allergy UK website has more information.


When to seek medical advice

If you ponder you or your kid may own a food allergy, it’s extremely significant to enquire for a professional diagnosis from your GP. They can then refer you to an allergy clinic if appropriate.

Many parents mistakenly assume their child has a food allergy when their symptoms are actually caused by a completely different condition.

Commercial allergy testing kits are available, but using them isn’t recommended.

Numerous kits are based on unsound scientific principles. Even if they are dependable, you should own the results looked at by a health professional.

Read more about diagnosing food allergies.


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