Woman with allergies sneezing

What are allergies?

An allergy is where your body's immune system reacts to something typically harmless to people, such as pollen (hay fever), dust, or cat hair. It is also possible to have allergic reactions to specific foods, such as peanuts, shellfish, or wheat.

Allergies are common, with up to 1 in 4 people suffering from allergies in the UK. Symptoms are mostly mild, but the reactions can be severe and even life-threatening for some people.

What causes allergies?


Allergies are caused by your immune system overreacting to a specific substance, resulting in symptoms such as a rash, swelling, or digestive problems.

Many things that cause allergies (allergens) are common, everyday substances.

While you may not react to an allergen immediately, over time, your body’s immune system learns to recognise these substances and starts to respond to them as though they are harmful. It is your immune system reaction that causes the symptoms of allergies.

Allergies are more common in children than adults. While many childhood allergies can improve as the child gets older, allergies can be for life. It is also possible for adults to develop allergies at any point in their lives to things they weren’t previously allergic to.


Common allergens


Substances that cause allergic reactions are known as allergens. While many things can cause an allergic reaction, some are considerably more likely to than others.

Common allergens include:

  • Tree and grass pollen (known as hayfever)

  • Dust mites (found in household dust)

  • Feathers

  • Animal fur – especially from household pets such as cats and dogs

  • Insect stings or bites

  • Some medicines, such as penicillin or ibuprofen

  • Foods, such as peanuts, dairy products, and eggs – see food allergies

What are the symptoms of allergies?


Symptoms of allergic reactions can vary greatly depending on how you come into contact with the allergen and the severity of your allergy.


Inhaled allergens


Inhaled allergens include pollen (hay fever), dust, and pet fur.


  • Runny nose

  • Sneezing

  • Coughing or breathlessness

  • Sore itchy eyes that may be red or watery (known as allergic conjunctivitis)

  • Itchy mouth, throat, nose and ears


Insect Bites or Stings


Common examples are mosquito bites and bee stings.

  • kin rashes, itching, or hives

  • Swelling of lips, mouth

  • Swelling of the throat, causing difficulty breathing

  • Dizziness

  • Stomach pain, vomiting, or diarrhoea


Contact Allergens


Some people are allergic to chemicals that commonly come into contact with the skin, such as the chemicals in cosmetics, the nickel in jewellery, or the latex found in gloves and condoms.

  • An itchy rash

  • Dry, cracked, scaly skin – typically on white skin

  • Blisters

  • Burning or swelling and tenderness of the skin


Food Allergies


Food allergies are typically mild, but reactions may be severe or even life-threatening.

Symptoms commonly include:

  • Stomach pain

  • Feeling or being sick

  • Diarrhoea

  • Feeling lightheaded

  • Itchy skin or hives (a raised rash)

  • Swelling of the lips or face

  • Coughing or wheezing

  • Difficulty breathing


Common, Legally Labelled Food Allergens


It is possible to be allergic to any food. However, the Food Standards Agency lists 14 common food allergens. Food manufacturers must clearly label these allergens on food packaging (or the information must be readily available in restaurants, such as on menus or upon request).

Common Food Allergens:

  • Celery

  • Cereals containing gluten (such as wheat and barley)

  • Crustaceans

  • Eggs

  • Fish

  • Lupin (sometimes found in flour and pasta)

  • Molluscs (shellfish, squid, octopus)

  • Mustard

  • Nuts

  • Peanuts

  • Sesame

  • Soya

  • Sulphur dioxide (sometimes called sulfites)


Common, Legally Labelled Food Allergens


Food intolerances are different from food allergies. A food intolerance is where you can’t digest certain foods properly. However, food intolerances can give rise to similar symptoms to food allergies.


  • Bloating

  • Flatulence (farting)

  • Diarrhoea

  • Stomach pain


Patch test

How Are Allergies Tested?


If you think you have an allergy, a doctor may refer you to a specialist. You may also have one of the following tests:

  • Skin prick/patch test, where a small amount of allergen is placed on your skin to see if it reacts

  • Blood tests

  • A controlled diet to test for food allergies or intolerances


How Are Allergies Treated?


  • Avoid the allergen, where possible

  • Medicines include antihistamines (like hay fever tablets) and steroid creams or tablets

  • Adrenaline auto-injectors (often called Epi-Pens) for severe allergic reactions

  • Desensitisation (immunotherapy). Only a medical professional should carry out such procedures


How Are Allergies Treated?


Some people may experience extreme, life-threatening reactions to allergens that can come on very quickly. Such severe reactions are known as anaphylaxis or anaphylactic shock.

Many people with extreme allergies will carry an adrenaline auto-injector with them. If the person is too unwell to inject themselves or tells you how to inject them, you can find instructions on the side of the device.

It would help if you always treated anaphylaxis as a medical emergency. Call 999 immediately, even if the person affected starts to feel better.

You Should Call 999 if:


  • Your lips, mouth, throat, or tongue suddenly become swollen

  • You’re breathing very fast or feel like you can’t breathe properly - you may feel wheezy, or feel like you’re gasping for air, or choking

  • You’re struggling to swallow, or your throat feels tight

  • Your skin, tongue, or lips turn blue, grey, or pale (if you have black or brown skin, this may be easier to see on the palms of your hands or the soles of your feet)

  • You suddenly become confused, drowsy, or dizzy

  • Someone around you experiences any of the symptoms above

  • Someone faints and they can’t be woken up

  • A child is limp, floppy, or not responding like they usually do (their head may fall to the side, backward or forwards, or they may find it difficult to lift their head or to focus on you)


You, or the person who’s unwell, may also have a swollen, raised, or itchy rash.

Someone who experiences these symptoms may carry an auto-injector (Epi-Pen). Ask them or check their pockets or bags if they cannot respond. Instructions on how to use them can be found on the side of the device.

If you think you or your family member might suffer from allergies, please don’t hesitate to contact a doctor or healthcare professional. If you aren’t registered with a GP yet, you can register online at any time using our simple online form.

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