Allergy is an inappropriate immune response to allergens. Allergen particles can be present in the air, such as pollen and mould spores, or on something you physically encounter such as chemicals at work.
Some people are more prone to allergy than others. These people are what is referred to as ‘atopic’. Atopic people are genetically predisposed to allergy. Atopy can be diagnosed if you suffer from allergy and a close member of your family also does.
Atopy is characterised by increased levels of a certain antibody in your blood called immunoglobulin E (you will usually see this written as ‘IgE’). Everyone has IgE in their body as IgE is used by the immune system to fight off parasites (like worms) but increased levels mean you are more likely to become ‘sensitised’ to allergens. The IgE in your body recognises proteins on the surface of allergens (you may see these proteins referred to as antigens) and sees them as a threat. The IgE attaches to other immune cells which send out signals to even more immune cells telling them the body is under attack and they need to react. This reaction can result in swelling, blood vessels becoming leaky and increased mucus production amongst other things. This is why your nose and eyes may run, you may get strange rashes and bumps on the skin, or you may find, if you are asthmatic, it triggers an attack.