In the main, hay fever refers to an allergy to pollen. If one is allergic to animals or house dust, this is referred to by doctors as ‘allergic rhinitis’. However, the terms ‘hay fever’ and ‘allergic rhinitis’ are often used interchangeably.
It has been estimated that up to 20% of people in Western countries suffer from hay fever. People prone to the condition tend to develop the problem during their teenage years and, although the condition lessens in severity with age, it can linger well into late adulthood.
Hay fever is associated with two other health conditions, eczema and asthma, in what doctors term the ‘atopic triad’. Someone suffering from one of these conditions is more likely to develop one or both of the others. Atopy, or this type of allergic tendency, can also run in families.
Hay fever is caused by an abnormal (or allergic) reaction of the body to pollen coming into contact with the nose, eyes or throat. The body’s immune system reacts to this usually ‘harmless’ substance as it thinks that, for some reason, it is ‘harmful’ – as if the body were being attacked by a potent virus.
As the immune system over-reacts, it releases large amounts of a chemical known as histamine. This causes itching, inflammation and irritation in the local tissue. Why the immune systems of people with hay fever over-react in this way is not known.
Pollen causing hay fever can come from grass, trees or flowers. In Canada pollen levels increase dramatically in spring as Nature comes to life.
As the weather warms up, grass, bushes, trees and other plants grow and develop in a coordinated fashion. In this way, pollen levels are highest during spring and early summer. In countries which are warm all year round, plants do not have these coordinated phases as they are able to grow and flower all year round. This explains why hay fever does not tend to be a problem in say, tropical countries.
Pollen levels in Canada are very much dependent on the weather. A week of dull rainy weather followed by a few days of warm sunshine, can drive pollen levels sky high – not good news for those with hay fever.