Allergy occurs when a person's immune system reacts to substances in the environment that are harmless for most people. These substances are known as allergens and are found in house dust mites, pets, pollen, insects, moulds, foods and some medicines.

Atopy is the genetic (inherited) tendency to develop allergic diseases.

People with atopy are said to be atopic. When atopic people are exposed to allergens they can develop an immune reaction that leads to allergic inflammation (redness and swelling).

This can then cause symptoms in the:

  • Nose and/or eyes - hay fever (allergic rhinitis/conjunctivitis)
  • Skin - eczema, hives (urticaria)
  • Lungs - asthma

A substance that is an allergen for one person may not be for another - everyone reacts differently. The likelihood (or risk) of developing allergies is increased if other family members suffer from allergy or asthma.