Millions of people in the UK live with at least one type of allergy.

An allergic reaction happens when the body mistakenly overreacts to the presence of a harmless substance. This is also known as a hyperreactive response.

During this, the immune system produces an antibody known as immunoglobulin E (IgE) and sends it to a specific area to fight off the perceived threat.

What are allergy symptoms?

The presence of IgE causes the body to release histamine which can cause numerous symptoms.

These can vary, but usually tend to affect the skin, the respiratory tract, the cardiovascular system and the gastrointestinal tract.

The most common types of reaction include:

  • Rhinitis, causing inflammation to the lining of the nasal passages. It can result in a runny or blocked nose, sneezing and itching.
  • Conjunctivitis, an inflammation of the part of the eye known as the conjunctiva. The eye can appear red as blood vessels dilate. The inflammation can also activate tear glands making the eyes water more than normal.
  • Breathing difficulties. Inflamed airways can cause irritation resulting in coughing, wheezing, shortness of breath and a tight feeling in the chest.
  • Urticaria, more commonly referred to as hives or wheals, is characterised by a red and raised rash. The skin can feel bumpy to touch and be very itchy.
  • Angioedema, which is swelling found under the skin occurring on the face, lips, eyes, hands and feet. This symptom is often present alongside urticaria and is typically associated with anaphylaxis.
  • Gastric pain, comprising of abdominal discomfort, diarrhoea and vomiting. It is generally associated with food allergies.
  • Eczema, characterised by dry, itchy and red skin patches, can be caused by direct contact with an allergen such as nickel (a metal used in jewellry) or ingested foods.

Severe allergic responses can result in anaphylactic shock which is a very serious and potentially life threatening condition.

When do allergies develop?

Allergies can manifest at any stage in someone’s life.

Someone may be exposed to a substance on numerous occasions and have no allergic reaction, but this can suddenly change.

It is thought that around 50 percent of people develop one or more allergy before the age of 18. If you are diagnosed with an allergy in childhood there is a possibility that your condition could improve as you grow older.

An estimated 44 percent of adults in the UK live with one or more allergy and the numbers are increasing every year.

Who is at risk of getting allergies?

Anyone can develop an allergy. However, the predisposition towards allergies is written in our genes.

  • 1 allergic parent = 33 percent chance of developing an allergy
  • 2 allergic parents = 70 percent chance of developing an allergy

These statistics cannot give an indication about which type of allergy might develop, as you do not necessarily inherit the same allergy as your parents.

Genetic predisposition means that your body’s immune system produces excess IgE antibodies, this is known as atopy. Being atopic does not always mean that you will develop an allergy but under certain circumstances there is a chance that your immune system might react disproportionately.

Environmental factors that can potentially increase your chances of developing an allergy include:

  • The use of antibiotics in childhood.
  • Exposure to pets and dust mites.
  • Growing up around smokers.

There has been some debate regarding whether or not there is link between babies born with a low birth weight and allergies.

What are the main allergy types?

In theory, you can be allergic to any substance. The most common allergy triggers can be broken down into several main groups: respiratory, contact, food and drugs.


Respiratory triggers cause the immune system to go into hyperactive response when they are inhaled.

Examples of these include:

  • Pollen. The pollen produced by a variety of plant life can cause unpleasant symptoms for many people with allergies. The invisible particles move through the air and stick to many surfaces making it difficult to avoid.
  • Mould. The spores released by mould can cause allergic reactions especially in damp weather and during harvest season.
  • Animal dander. Domestic pets can cause problems for those with allergies. When an animal grooms itself it distributes these particles onto its fur which can easily become airborne and subsequently breathed in.
  • Dust mites. Microscopic house mites thrive in our warm homes where they can live off the skin that we shed as well as our sweat and exhaled breath. Their faeces are very dry so the particles are easily inhaled deep into our respiratory system.


When your skin comes into direct contact with a material allergen your immune system tries to fight it off as though it were an infection resulting in numerous symptoms.

Contact allergens might be:

  • Latex. Irritant contact dermatitis is the most common form of allergic reaction to latex products. A severe itchy rash forms on the skin.
  • Insect bites or stings. The sting area becomes swollen and itchy. This allergen can lead to anaphylaxis in a small portion of people and can be fatal.


If the body produces too much IgE when a particular food is consumed it can trigger a whole range of responses depending on where the reaction takes place.

Common trigger foods include:

  • Fruits
  • Egg
  • Nuts
  • Seafood


All medications have the potential to cause side effects for anyone that uses them. However, a small amount of people will experience true allergic reactions causing dermatitis or fever-like symptoms.

The drugs which more commonly induce allergic reactions are:

  • Antibiotics
  • Anaesthetics
  • Contrast injections used in x-ray diagnostics

Why are allergy cases increasing?

There are numerous theories behind the reason for the rise in the number of allergies but a definitive cause has not yet been identified.

The main theories include an increase in pollution, a decline in early exposure to bacteria (hygiene hypothesis) and a change in human genetic makeup making more people predisposed to allergies.

The increase in allergies is currently limited to western countries and industrialised nations. This supports the theory that higher levels of pollution are playing a part in the increase in allergies being diagnosed.

It is thought that an increase in the number of atopic people leads to an increase in actual allergies. However, that being said, changes in human genetics take many years and so the current increase in allergies cannot be solely attributed to the higher prevalence of allergic genes.

The hygiene hypothesis is built around an understanding that today we are not exposed to the same amount of bacteria at an early age as we were in the past. This is thought to be due to an increased use of antimicrobial substances in domestic and industrial cleaning and a reduction in the amount of contact between young children and farm animals.

It is suggested that in order for our bodies to build up a sufficient immune system we need to come into contact with these elements at an early stage in our lives. Research continues into the area to establish whether a better understanding could improve allergic therapies.

Page last reviewed:  08/03/2017