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Allergy

Bowls of nuts

What is an allergy?

An allergy is the reaction of the body’s immune system to harmless substances such as pollen, food and dust mites. In people with allergies, the body falsely identifies these substances as a threat, and tries to fight them off.

Why do people have allergies?

No one knows exactly, but research has shown that there are a number of risk factors which increase a person’s chances of having an allergy:

  • Genetics. Normally, a child has a one in five chance of developing an allergy. However, the risk is doubled in children who have one parent with allergies. If both parents have allergies, there is a 60-80% chance that the child will develop them too.
  • Asthma and other allergies. Having asthma increases your chance of developing an allergy. Furthermore, having one type of allergy increases the chances of becoming allergic to something else.

What are common allergies?

Allergy is a very common condition, affecting one in three people in the UK at some point in their lives. Around half of those affected are children.

Common allergies include:

  • Pollen from trees and grasses. This type of allergy is known as hay fever.
  • Foods such as peanuts, milk and eggs
  • Dust mites. Actually, the allergy is to proteins secreted in the faeces of these mites, not to the mites themselves.
  • Moulds
  • Furry or hairy animals, such as dogs, cats, horses, rabbits or guinea pigs
  • Wasp or bee stings
  • Medicines, such as penicillin

Why are allergies becoming more common?

Each year in the UK, the number of people with allergies increases by 5%. While the cause of this is unknown, there are two main hypotheses:

  • Our environment is too clean. There is a hypothesis that more people are developing allergies because the environment that they have grown up in is too clean. Studies suggest that our immune system needs to come into contact with bacteria and micro-organisms during infancy in order for the body to respond appropriately to them later in life. If babies and toddlers are not exposed to animals, dirt and dust, their bodies may not recognise these substances as harmless when they are older.
  • Changes in diet. Our diet today is very different to what people ate a few decades ago. Some people have suggested that the reduction in vitamin levels in our diet, and the increase in processed foods, might be contributing to the rise of allergies. However, there is no hard evidence for this.

What happens during an allergic response?

When someone who has an allergy comes into contact with an ‘allergen’ (the substance that they are allergic to), their body reacts in a certain way. The body’s antibodies (which are usually used to fight off disease) attach themselves to certain cells. When the allergen comes into contact with the antibodies, they release a chemical called histamine. This causes the surrounding tissue to swell, itch and become inflamed, and it is this which causes the symptoms of an allergic reaction.

What are the symptoms of an allergic reaction?

Common symptoms of an allergic reaction include:

  • sneezing
  • coughing
  • sinus pain
  • swelling
  • itchy mouth, throat, eyes and ears
  • shortness of breath
  • nausea, vomiting and diarrhoea

Some allergic reactions may simply be inconvenient, such as hay fever, but others, such as peanut allergy, can be fatal if not treated medically.

How can allergies be treated?

There are many different ways to treat allergies, and the first step in determining which way is best for you is to see your GP.

If you don’t know what’s causing your allergic reaction, your GP can help work it out. It will be helpful for him/her if you keep a diary of when and where symptoms occur.

Once you know what you are allergic to your doctor may advise a number of ways of managing your allergy. One of the main ways is to simply try and avoid your allergen as much as possible. If you are allergic to cats, you should probably not keep one in the house, while if you have a nut allergy you should obviously not eat foods containing nuts.

However, it is often impossible to avoid allergens altogether and there are a number of medicines that can relieve symptoms when they occur. 

Antihistamines

Antihistamines are probably the best known type of allergy medicine, and most are available from a pharmacy without a prescription (although some, such as Telfast, are prescription-only). These medicines work by blocking the action of histamine, which is the chemical that causes symptoms during an allergic reaction.

In the past, antihistamines usually had the side effect of causing drowsiness, which was often very inconvenient for allergy sufferers who had to take them regularly. However, most modern antihistamines don’t come with the side effect of drowsiness.

Antihistamines are usually taken as tablets, but can also come in the form of syrups, creams, nasal sprays or eye drops.

Corticosteroids

Corticosteroids are another type of medicine used to treat allergic reactions. They are a form of steroid which is identical to the natural hormone, cortisol, which is produced by the body. Steroids reduce inflammation, and are often used for the treatment of asthma (inhalers contain steroids) in order to reduce swelling of the airways.

Adrenaline

Adrenaline is used to treat severe allergic reactions such as those to peanuts and wasp stings. In these cases, the sufferer can go into anaphylactic shock when the sudden high levels of histamine can cause difficulty breathing, and even loss of consciousness. Adrenaline is administered via an injection (such as EpiPen), which should be carried at all times by people who have severe allergies.

How to get help

For more information on hay fever and EpiPens you can visit our Allergy Clinic.

The NHS have an allergy helpline, 01322 619898 (Monday-Friday; 9am-5pm), which you can call for advice on managing allergies.

Allergy UK also offers a series of downloadable books and leaflets on allergies; click here to browse.

In the case of a severe allergic reaction, you must call 999 or go to your nearest Accident and Emergency Department as soon as possible.