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Allergy is the term used to describe an adverse (bad) reaction that the body has to a particular substance. Most things that cause allergies are not harmful, and have no affect on people who are not allergic.

The reason for the rise of allergies in unclear. Some experts believe it is associated with pollution. Another theory is that allergies are a result of us living in a cleaner, germ-free environment. By reducing the number of germs our immune system has to deal with, it overreacts when it comes into contact with harmless substances.

There have been many studies trying to prove whether or not these theories are correct, but the results have been inconclusive and further research is needed.


Allergens and allergic reactions


Any substance that triggers an allergic reaction is called an allergen. There are many different types of allergens, but three of the most common are pollen, dust mites and nuts.

Allergic reactions can cause a range of symptoms. Some can be quite mild, and some are more serious.

An allergy develops when an allergen triggers the immune system, the body's natural defence against germs and viruses. The immune system wrongly recognises the allergen to be a threat, and releases chemicals called antibodies to destroy it. It is the release of antibodies that causes the symptoms of an allergic reaction.

Where the allergic reaction takes place depends on how you came into contact with the allergen. Contact may be with your skin, or with the lining of your lungs, mouth, throat, stomach or intestine.


In rare cases, allergic reactions can be very serious. This is called anaphylactic shock. It is a sudden, severe allergic reaction that involves the whole body and it usually happens within minutes of coming into contact with a particular allergen.

The symptoms of anaphylactic shock affect the respiratory and circulatory system and include the following:

  • raised blood pressure,
  • swelling, and
  • breathing difficulties.

If you have anaphylactic shock, you will require emergency treatment, usually with an injection of a medicine called adrenaline. If you suspect that you or someone you know is having anaphylactic shock, you should immediately dial 999 and ask for an ambulance.

If the diagnosis shows that your allergy could cause anaphylactic shock, or you have had a severe allergic reaction in the past, you will be given an auto-injection kit of adrenaline.


Allergies are caused by the body's immune system reacting to allergens as if they were harmful. The immune system does this by making antibodies to fight off the allergen. Antibodies are special proteins made in the immune system to fight off viruses and infections that could harm us.

When the body comes into contact with an allergen, the antibody released is called immunoglobulin E (IgE). This antibody causes other blood cells to release more chemicals, including histamine (a protein that is involved in many allergic reactions), which together cause the symptoms of an allergic reaction. Histamine causes most of the typical symptoms that happen in an allergic reaction. For example it:

  • makes your muscles contract, including those in the walls of the air tubes of your lungs,
  • increases the amount of fluid that is released from small veins, causing membranes to swell.
  • increases the amount of mucus produced in your nose lining, and causes local itching and burning.


Some people are predisposed to allergy. This means that they are more likely to develop an allergy because it runs in their family. If you are predisposed to an allergy, the condition is called atopy. People who are atopic are more likely to develop allergies because their body produces more IgE antibody than normal.

Although atopy is inherited, environmental factors also play a part in the development of allergic disorders.
The exact role that the environment plays is unknown, but studies have shown that a number of factors seem to increase the chance of a child developing atopy. These include:

  • growing up in a house with smokers,
  • exposure to dust mites,
  • exposure to pets, and
  • using antibiotics.

Boys are more likely to develop atopy than girls, as are babies who have a low birth weight. The reasons for this are unclear.

There are thousands of allergens. Some of the most common include:

  • house dust mites,
  • grass and tree pollens,
  • pet hair or skin flakes,
  • fungal or mould spores,
  • food (milk, egg, wheat, soya, seafood, fruit and nuts),
  • wasp and bee stings,
  • certain medication, such as penicillin, aspirin or types of opiates like codeine,
  • latex, and
  • nickel, rubber, preservatives and chemical resins.

You will need to tell your GP about the symptoms you are having, when they happen, and how often they occur. Your GP will want to know if any family members have similar symptoms, or if there is a family history of allergy. You should also think about any triggers that seem to cause a reaction, and whether it happens at a particular place or time.

Your GP will probably carry out tests to identify the allergen that is causing your symptoms. Or, you may be referred to an NHS or independent allergy clinic.

Even if you think you know what is causing the allergic reaction, you may need to be tested in order to determine the exact allergen.

There are several different tests that can be carried out:

  • Skin prick test - this is usually the first test to be carried when looking for an allergen. The skin is pricked with a tiny amount of the suspected allergen to see if there is a positive reaction. If there is a positive reaction, your the skin will become itchy, red and swollen.
  • Blood test - this is used to measure the amount of IgE antibody in your blood that has been produced by the immune system in response to a suspected allergen. The results, given on a scale from zero to six, are available in one to two weeks. Zero indicates a negative result and six indicates an extremely high sensitivity.
  • Patch test - this test is used to find the allergen causing eczema or contact dermatitis. A small amount of the suspected allergen is added to special metal discs and they are then taped to your skin, usually for 48 hours, to see how it reacts. This test is usually carried out in dermatology (skin) departments in hospital.

Wherever possible, the most effective way of treating allergies is to avoid all contact with the allergen causing the reaction.

There are many drugs available to treat the common symptoms of allergies, such as runny nose, itchy mouth and sneezing. Many of these treatments are available over the counter. Ask your pharmacist or GP for advice. 


Antihistamines treat allergies by blocking the action of the chemical histamine, which the body releases when it thinks it is under attack from an allergen. Antihistamines can be taken in tablet, cream and liquid form. They can also be taken in the form of eye drops and nasal drops. 


Decongestants help to relieve symptoms such as a blocked nose, which is often caused by hayfever and dust and pet allergies. Decongestants can be taken as tablets, capsules, nasal sprays or in liquid form. 

Nasal sprays and eye drops 

Nasal sprays can be used to reduce swelling and irritation in your nose, and eye drops will help to relieve sore, itchy eyes. However, some sprays and drops are only suitable for adults. Ask your GP or pharmacist for advice before buying treatments for children. 

Leukotriene receptor antagonists 

Leukotriene receptor antagonists work by blocking the effects of leukotrienes - chemicals released during an allergic reaction that cause inflammation of your airways. They are normally used in the treatment of asthma when other treatments have proved ineffective. 

Other medicines 

Medicines such as sodium cromoglicate and corticosteroids can be used regularly to stop symptoms developing. These are commonly available as nasal sprays and eye drops. 

Hyposensitisation (immunotherapy) 

Another form of treatment for allergies is hyposensitisation, which is also sometimes known as immunotherapy. It can be used to help people who have a specific allergy to something like bee stings.

You will gradually be introduced to more and more of the allergen to encourage your body to make antibodies that will stop future reactions.

This type of treatment must only be carried out under the close supervision of a doctor because there is a risk that it may cause a serious allergic reaction called anaphylactic shock (see 'complications' section).

Hyposensitisation is normally only recommended for the treatment of hayfever that has not responded to other treatment, and for allergies to bee and wasp stings.

Treating anaphylaxis

Less than one in 1000 people with an allergy experience a severe allergic reaction (anaphylaxis). These are treated with an adrenalin injection, called an epi-pen or anapen, which you usually administer yourself. Use the adrenaline injection as soon as you experience respiratory symptoms, such as difficulty breathing, and call for emergency medical help. If your symptoms are not relieved within five to 10 minutes, you’ll need another injection to help get your symptoms under control.

Your doctor or an allergy consultant can prescribe adrenaline injections. If you have severe allergic reactions, carry two with you at all times.


The best way to prevent an allergic reaction is to avoid the allergen that causes it. However, this is not always easy. Allergens such as dust mites or fungal spores can be hard to spot and can breed in even the cleanest house.

It can be hard to avoid pets, particularly if they belong to friends and family, and many food allergies are triggered because people do not realise they are eating it. Below is some practical advice that should help you to avoid the most common allergens.

House dust mites

One of the biggest causes of allergies are dust mites. Dust mites are microscopic insects that breed in household dust. Below are a number of ways that you can limit the amount of mites in your house.

  • Choose wood or hard vinyl floor coverings instead of a carpet.
  • Fit roller blinds that can be easily wiped clean.
  • Remove cushions, soft toys and other upholstered furniture.
  • Use synthetic pillows and acrylic duvets, instead of woollen blankets or feather bedding.
  • Use a vacuum cleaner fitted with a HEPA (high efficiency particulate air) filter, because it can remove more dust than ordinary vacuum cleaners.
  • Wipe surfaces with a damp, clean cloth, as dry dusting can spread the allergens further.

Food allergies

By law, food manufacturers must clearly label any food that contains something that is known to cause a food allergy, such as celery, cereals, crustaceans, eggs, fish, milk, mustard, nuts, sesame seeds, soybeans and the preservatives sulphur dioxide and sulphites. By carefully checking the label for the list of ingredients, you should be able to avoid an allergic reaction.

Many people experience an allergic reaction while eating out at a restaurant. Ways to avoid this are outlined below.

  • Do not rely on the menu description alone - many sauces or dressings could contain allergens.
  • Communicate clearly with the waiting staff and ask their advice.
  • Simple dishes are less likely to contain 'hidden' ingredients.
  • Avoid places where the is a chance that different types of food could come into contact with each other, such as buffets or bakeries.

Pollen allergies

Pollen allergies, more commonly known as hayfever, are caused when plants release pollen particles (pollinate). Different plants pollinate at different times of the year, so when you get hayfever will depend on what sort of pollen(s) you are allergic to. Typically, people are affected during spring and summer. To avoid exposure to pollen you can:

  • Check weather reports for the pollen count, and stay indoors when it is high.
  • Wear wrap-around sunglasses to protect your eyes from pollen.
  • Keep doors and windows shut during mid-morning and early evening, as this is when there is most pollen in the air.
  • Avoid grassy areas, such as parks and fields.
  • Get someone else to cut the grass for you.

Severe allergies

If you have ever had a severe allergic reaction (anaphylaxis), carry two epi-pens or anapens with you at all times. Wear a Medic Alert or Medi Tag medallion or bracelet, so people are aware of your allergy in an emergency, and consider telling your teachers, work colleagues and friends so they can administer your adrenaline injection in an emergency and call an ambulance. Following this advice could save your life


Allergic reactions do not happen the first time you come into contact with the allergen, but at a later point of contact. This is because the body has to develop sensitivity to something before it can become allergic to it.

Allergic reactions produce many different symptoms and affect people in different ways. Some of the most common symptoms include the following:

  • sneezing,
  • wheezing,
  • sinus pain (feelings of pressure or pain high up in the nose, around the eyes and at the front of the skull),
  • runny nose,
  • coughing,
  • nettle rash/hives,
  • swelling,
  • itchy eyes, ears, lips throat and palate (roof of mouth),
  • shortness of breath, and
  • sickness, vomiting and diarrhoea.

It is important to remember that these symptoms can also be caused by conditions other than allergies, and some may be illnesses themselves. See your GP or ask your pharmacist for advice if you are not sure what is wrong.

Allergies are not the same as an intolerance

There is a difference between an allergy and an intolerance to certain substances, such as a lactose intolerance (lactose is a sugar found in milk). An allergic reaction always involves your immune system and can be tested by measuring specific immune responses. An intolerance does not involve your immune system, so allergy tests will not highlight the problem.

People with an intolerance to certain foods can typically eat a small amount without having any problems. In contrast, people with a food allergy will have a bad reaction if they come into contact with even the tiniest amount of the food that they are allergic to.