The reasons for the increased incidence of allergies are unknown but there are a number of common factors that have been suggested for these increases:

• Increased exposure to allergens such as pollution.
• Genetics €“ 1 in 5 UK children are pre-disposed to developing an allergy but children with one parent who suffers from an allergy have their risk doubled. Where both parents suffer allergies the risk increases to 60-80 per cent.
• Hygiene hypothesis - increased domestic cleaning means that children are living in an increasingly clean environment with reduced exposure to bacteria which is necessary to stimulate development of an effective immune system.

Some patients confuse an allergy with intolerance or sensitivity to a substance. It is important that the differences between these are understood since the severity of the symptoms are different.

• Allergy €“ a reaction by the body's immune system, involving the production of antibodies, to a substance that would normally be harmless.
• Sensitivity €“ this is an exaggerated side effect to a normal substance e.g. a localised reaction by the skin to perfume.
• Intolerance €“ this does not involve the immune system and its causes are not well understood. Intolerance is usually associated with food and patients can often tolerate a small amount of the offending substance without symptoms, whereas someone with a food allergy only needs to come in to contact with a small amount and they have serious symptoms. Intolerance is more likely to be delayed where symptoms develop hours or sometimes days after exposure.

Symptoms of Allergies 

The symptoms associated with an allergy will depend on the allergen or the site of the body affected but can include: