Introduction
Allergy is the word used to describe an adverse (bad) reaction that the body has to a particular food or substance in the environment.
Most substances that cause allergies are not harmful and have no effect on people who are not allergic.
The allergic response
Any substance that triggers an allergic reaction is called an allergen. Some of the most common allergens include pollen, house dust mites, mould and pets. Less common allergens include nuts, fruit and latex.
An allergy develops when the body s immune system reacts to an allergen as though it is a threat, like an infection. It produces antibodies to fight off the allergen, in a reaction called the immune response.
The next time a person comes into contact with the allergen, the body "remembers" the previous exposure and produces more of the antibodies. This causes the release of chemicals in the body that lead to an allergic reaction.
Common allergic disorders include asthma, eczema and hay fever. Symptoms of an allergy can include sneezing, wheezing, coughing and skin rashes.
The nature of the symptoms depend on how you came into contact with the allergen. For example, you may experience problems with your airways if you breathe in pollen.
Seeing your GP
If you think you have an allergy, tell your GP about the symptoms you are having, when they happen, how often they occur and if anything seems to trigger them.
You may be offered a skin prick test to identify the allergen that is causing your symptoms.
Read more about the diagnosis of allergies.
How common are allergies?
Allergies are very common. According to Allergy UK, one-in-four people in the UK suffers from an allergy at some time in their lives. The numbers are increasing every year and as many as half of those affected are children.
The reason for the rise is unclear. Some experts believe it is associated with pollution. Another theory is that allergies are caused by living in a cleaner, germ-free environment, which reduces the number of germs our immune system has to deal with. This causes it to overreact when it comes into contact with harmless substances (read more about the common causes of allergies).
Managing an allergy
The most effective way of managing an allergy is to avoid all contact with the allergen causing the reaction. Taking medication can't cure your allergy, but it can treat the common symptoms.
Read more about treating an allergy and preventing an allergic reaction.
Allergy, sensitivity or intolerance
Allergy this is a reaction produced by the body s immune system when it encounters a normally harmless substance.
Sensitivity this is the exaggeration of a normal side effect produced by contact with a substance. For example, the caffeine in a cup of coffee may cause extreme symptoms, such as palpitations and trembling, when it would usually only have this effect when taken in much larger doses.
Intolerance this is where a substance (such as lactose) causes unpleasant symptoms (such as diarrhoea) for a variety of reasons, but does not involve the immune system. 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 even if they come into contact with a tiny amount of the food to which they are allergic.
