What is pollen?
There are about 30 different types of pollen, with different trees and plants producing their pollen at different times of the year.
Depending on which pollen you are allergic to, you may experience your hay fever symptoms at different times. It’s possible to be allergic to more than one type of pollen.
Research suggests that pollution, such as cigarette smoke or car exhaust fumes, can make allergies worse.
How does pollen affect the body of someone with hay fever?
When these tiny particles come into contact with the cells that line your mouth, nose, eyes and throat, they irritate them and trigger an allergic reaction, to become swollen, irritated and inflamed.
When you have an allergic reaction, your body overreacts to something it perceives as a threat. In hay fever, the allergen (the substance you are allergic to) is pollen. Your immune system (the body’s natural defence system) starts to respond as if it were being attacked by a virus.
Your immune system will release a number of chemicals designed to prevent the spread of what it wrongly perceives as an infection.
These chemicals then cause the symptoms of the allergic reaction, such as watering eyes and a runny nose.
When is pollen at its worst?
That depends on what kind of pollen you are allergic to. In the UK, the pollen count season is usually separated into three periods.
Pollen Count Calendar
Spring
Tree Pollen
About 25% of people in Britain with hay fever are allergic to pollen from trees, including oak, ash, cedar and birch (people with an allergy to birch often also experience an allergic reaction to apples, peaches, plums and cherries as these types of fruit contain a similar protein to birch pollen)
Late Spring – Early Summer
Grass Pollen
About 90% of people in Britain with hay fever are allergic to grass pollen
Early Spring – Late Autumn
Weed Pollen
Including pollen from dock, mugwort and nettles.
However, the pollen count season can sometimes begin as early as January, or end in November.
The pollen count
The pollen count is the number of grains of pollen in one cubic metre of air. Hay fever symptoms are likely to be worse if the pollen count is high.
How is the pollen count recorded?
Air samples are collected in traps set on buildings two or three storeys high. Taking samples from this height gives a better indication of the pollen in the air.
Traps on the ground would only collect pollen from nearby trees and plants.
The air is sucked into the trap and the grains of pollen are collected on either sticky tape or microscope slides (glass plates). The pollen is then counted. Samples are normally taken every two hours, and usually the results are averaged over a 24-hour period.
When will the pollen count have an effect on hay fever?
Hay fever symptoms usually begin when the pollen count is over 50.
Low
Fewer than 30 grains of pollen in every cubic metre of air
Moderate
30-49 grains of pollen in every cubic metre of air
High
50-149 grains of pollen in every cubic metre of air
Very High
150 or more grains of pollen in every cubic metre of air
The pollen count is usually given as part of the weather forecast during the spring and summer months.
The effect of the weather
The amount of sunshine, rain or wind affects how much pollen plants release and how much the pollen is spread around.
- On humid and windy days, pollen spreads easily.
- On rainy days, pollen may be cleared from the air, causing pollen levels to fall.
- On sunny days, the pollen count is highest in the early evening.
- During their pollen season, plants release pollen early in the morning.
- As the day gets warmer and more flowers open, pollen levels rise.