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.
Allergies are very common and affect around one in four people in the UK at some time in their lives. The number of people affected by allergies rises every year. For example, one study showed that the number of children allergic to nuts doubled in a 10-year period.
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.
