What causes allergies?

Bupa Logo at the reception
Consultant in allergy, Cromwell Hospital
18 June 2024
Next review due June 2027

Allergies are common – they affect 1 in four people in the UK. But what causes them? Here I’ll explain the key processes that drive allergies, and what you can do to manage yours.

A person studying a test tube

What types of allergies are there?

There are six main types of allergies:

  • food (such as milk protein, egg, nuts, and shellfish)
  • insects (such as bee and wasp stings)
  • airborne (such as pollen, animal fur, dust, and mould)
  • drugs (such as penicillin, pain killers, and general anaesthetics)
  • latex (such as gloves and balloons)

Usually allergies begin in childhood, but you can also develop them later in life. You may be allergic to just one type of allergen (such as pollen), or you could have multiple allergies.

Allergy symptoms can be mild to severe. Most symptoms come on quickly which can help you to tell the difference between an allergy and other conditions.

What causes the body to develop allergies?

Your immune system usually does a good job at deciding what is dangerous or not. But with allergies, it overacts. It mistakenly reacts to harmless proteins within food, pollen, or other allergens.

Your body doesn’t become allergic the first time it encounters an allergen. It first goes through a phase called sensitisation.

When this happens, your body starts to produce a specific type of antibodies (proteins made in response to foreign particles) called immunoglobin E (IgE). Then, when your body encounters its trigger (the allergen) again, the relevant antibodies start an inflammatory (allergic) reaction.

Here, your body releases histamine and other inflammatory chemicals such as cytokines. This leads to allergy symptoms such as:

  • itchy eyes, nose, mouth, or skin
  • sneezing
  • coughing
  • hives
  • swellings
  • vomiting
  • stomach pain

Sometimes, during an allergic reaction, you can have a very severe response which is known as anaphylaxis. This is a life-threatening emergency that always requires medical attention. Symptoms of anaphylaxis include:

  • feeling faint or dizzy due to low blood pressure
  • difficulty breathing or chest tightness
  • fast pulse
  • swelling in the throat and hoarse voice

How do you test for allergies?

You will usually have a skin test and/or a blood test to confirm that your symptoms are caused by an allergy. Both tests will look for evidence of specific IgE antibodies, which indicate you have been sensitised to an allergen.

Skin prick tests are used for allergies such as hay fever, food allergy, venom allergy or some suspected drug allergies, like penicillin. Here, small amounts of allergen extracts (such as pollen or milk protein) in the form of a drop, are put on your skin and left for 15 to 20 minutes. This gives them time to react with antibodies in the skin.

A doctor will then check to see if you have a reaction – for example if your skin has become red and itchy.

If a food allergy is suspected, a medical professional may suggest you cut out the suspected trigger foods to see if your symptoms reduce.

Can you prevent allergies?

You can’t completely protect yourself from developing an allergy. But there’s some interesting research suggesting early life allergen exposure may help. This is when young children are introduced to foods such as peanuts in small doses.

One study showed that children fed peanuts from 4 to 6 months upwards had less peanut allergy as teenagers. They were over 70 per cent less likely to develop an allergic reaction to the peanuts and other legumes, – which could have a substantial effect on long term allergy risk.

How are allergies treated?

Allergy treatment varies depending on the type and severity of your reaction. Here are some of the common approaches to managing allergies:

Avoid your triggers

If you have an allergy, you’ll need to try and avoid your allergens going forwards. How hard this is will depend on what you’re allergic to. For example, with hay fever, it’s usually hard to completely avoid pollen during the spring and summer. This is because pollen is airborne and spreads far and wide – making it easy to breathe in when out and about.

For some allergies you may need to take treatments to reduce your symptoms. This can include taking:

With food allergies, it’s very important to avoid your trigger foods, as this type of allergy is more likely to trigger a severe reaction than a pollen allergy. Some people need to carry an adrenaline auto injector – otherwise known as an epi-pen. This is used if you have anaphylaxis.


For some allergies there’s also a treatment called immunotherapy. This involves slow exposure to your allergen in a safe and controlled environment. This should desensitise your immune system, so you don’t react as much. It’s only done under medical supervision, when you can be monitored and treated for a severe reaction. Speak to a doctor for more advice about managing your specific allergy.

You can’t predict when you might want to see a GP, but you can be ready for when you do. Our GP subscriptions are available to anyone over 18 and give you peace of mind, with 15-minute appointments when it suits you at no extra cost.

Bupa Logo at the reception
Dr Florentina Dumitru
Consultant in allergy, Cromwell Hospital



Julia Ebbens, Health Content Editor at Bupa UK

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