What is an allergy?

An allergy is an immune reaction by the body to a particular food or substance, for example peanuts or pollen. Symptoms can vary from mild, like sneezing, to life-threatening, known as anaphylaxis. Allergic diseases include hay fever, asthma and food allergies, and it’s estimated that around 44 per cent of adults and 50 per cent of children have an allergy.


Other related allergies include coeliac disease, which is an adverse reaction to gluten, and eosinophilic oesophagitis (EoE) where a build-up of immune cells in the oesophagus cause inflammation, leading to difficulty swallowing.

Food allergies are different to food intolerances and food sensitivities. A food sensitivity is still a reaction of the immune system to a certain food, but it’s not life-threatening. A food sensitivity may cause symptoms such as diarrhoea, stomach pain, headaches, or hives.

A food intolerance is not related to the immune system, but is the inability to process or digest a certain food such as lactose, due to the lack of a specific digestive enzyme (e.g. lactase).

Next, read 10 foods to support your seasonal allergies and food intolerance tests: are they worth it? Don't forget to check our recipes made without nuts, dairy and gluten.

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Bowl of peanuts and an inhaler

What are common allergies?

Common allergies include:

  • Tree and grass pollen
  • Dust
  • Foods including celery, cereals containing gluten (such as wheat, barley and oats), crustaceans (such as prawns, crabs and lobsters), eggs, fish, lupin (a type of legume), milk, molluscs (such as mussels and oysters), mustard, nuts, sesame, soy beans and sulphur dioxide
  • Animals, such as cats and dogs
  • Insect stings, such as those from bees and wasps
  • Certain medications such as penicillin, antibiotics and aspirin

Allergies are the most common chronic disorder in the UK, both in children and adults. In fact, in the last 20 years, the number of people with a peanut allergy has risen five-fold, with around one in 50 children now having an allergy to peanuts. You can read more in our guide to nut allergies.

What are common allergy symptoms?

Symptoms can vary from person to person and depend on what type of allergy it is.

Seasonal (hay fever), dust and animal allergies:

  • Sneezing
  • Coughing
  • A runny or blocked nose
  • Itchy, red or watery eyes
  • Loss of smell
  • Headache
  • Earache
  • Fatigue


  • Wheezing
  • Breathlessness
  • A tight chest
  • Coughing

An asthma attack can appear with more severe symptoms such as:

  • Constant wheezing or coughing
  • A very tight chest
  • Too breathless to eat, sleep or speak, or breathing faster
  • A fast heartbeat
  • Blue lips and fingers
  • Fainting

If asthma medication does not improve symptoms, it’s important to call 999 and seek medical attention. Read more on the NHS website.

Food allergy symptoms include:

  • Itchy skin or raised bumps or rash (hives)
  • Swelling of the face, lips and eyes
  • Itchy throat, coughing, wheezing, breathlessness or loss of voice
  • Feeling dizzy or light-headed
  • Sneezing, runny or blocked nose
  • Nausea or vomiting
  • Stomach pain
  • Diarrhoea

These symptoms may occur immediately or a few days after eating the food.

However, signs of a serious allergic reaction are a medical emergency, and you must call 999 immediately.

These signs include:

  • Lips, mouth, throat or tongue suddenly become swollen and having trouble swallowing
  • Breathing becomes very fast or struggling to breathe – this can look like choking or gasping for air
  • Skin, tongue or lips turn blue, grey or pale (it may be easier to see colour changes on palms or soles of feet for darker skin tones)
  • Fainting without being woken up
  • A child becomes limp, floppy or is not responding – their head may fall to the side, backwards or forwards or they may find it difficult to lift their head or focus on your face
Woman suffering from hay fever with watering eyes

What causes an allergy?

While no-one knowns exactly why allergies are rising so quickly here in the UK, there are a few thoughts behind possible causes:


Children who have a parent or grandparent with an allergy are at an increased risk of developing an allergy themselves. If one parent has an allergy, the risk is doubled, but if both parents have allergies, then this risk increases to between 60-80 per cent.

The hygiene hypothesis

As children, being exposed to germs is thought to help strengthen and develop the immune system. This can then help to protect against the development of allergies or asthma.

However, in today’s modern world we have become overly clean. The use of chemical cleaning products, antibacterial solutions and antibiotics mean that we, and especially children, are being exposed to less and less germs than our ancestors, which is having a detrimental effect on the immune system.

Changes in our diet

Western diets have become more and more reliant on processed and ultra-processed foods, which means we are not getting as many of the essential nutrients to support the immune system.

There is also evidence that fewer food choices in the first year of life is associated with increased risk of allergies and asthma in infancy, compared to those who have a greater variety of food which reduces the risk and may offer protection against allergies, asthma and food sensitisation. You can read more in our article on allergies in children.

Poor diets also impact the gut microbiome, which plays a crucial role in the immune system. About 80 per cent of the immune system is in the gut, and changes to the microbiome can increase the risk of developing food allergies.

Pollution and environmental factors

As the world becomes more crowded, there is more urbanisation and industrialisation. This in turn has meant greater air pollution and exposure to toxins in the environment, which is impacting our immune systems but also those of children. Air pollution alone has been found to have an adverse effect on respiratory health, which can make pollen more allergenic and increase the total pollen count.

Vitamin D deficiency

Vitamin D is an essential nutrient that helps keep our immune system healthy and is important for lung development. However, vitamin D deficiency is now common as more of us work indoors, use sunblock or actively avoid spending time in the sun. Therefore, low vitamin levels lead to a lower immune status which can increase the risk of allergic disorders.

Gluten-free bread

What can we do to live safely with an allergy?

If you suspect you or your child has an allergy, then speak to your GP about possible tests that can be done to determine the cause. These include:

  • A skin prick or patch test, whereby a small amount of the allergen is put on the skin to see if there is a reaction.
  • Blood tests to check for allergens.
  • A special diet that eliminates the possible allergen foods, to see if symptoms get better.

There are then several steps that can be taken to help someone living with an allergy:

  • Avoiding the allergen as much as possible, whether that is a food, pollen, dust, or a pet.
  • Medication may help such as antihistamines or steroids, or an auto-injectable device (eg. EpiPen) may be required for those with severe allergic reactions.
  • Immunotherapy is still a relatively new therapy for those with severe allergic reactions. This involves exposing the individual to the known allergen, in small amounts and over time so that the body gradually gets used to it and reduces its reaction. This should be only done with advice from a medical professional.
  • For food allergies, eating out of the home can increase the risks so it is important to plan ahead, call the restaurant and check that they can effectively cater for allergies, read food labels carefully, and be prepared for emergencies by always having your medication with you.

Want more like this? Now read...

What is hay fever?
Wheat allergy in children
What is a low-histamine diet?
Top 10 natural hay fever remedies
A guide to high-histamine foods

Nicola Shubrook is a nutritional therapist and works with both private clients and the corporate sector. She is an accredited member of the British Association for Nutrition and Lifestyle Medicine (BANT) and the Complementary & Natural Healthcare Council (CNHC). Find out more at urbanwellness.co.uk.


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