Watch the latest Pollen forecast for ITV Wales with Ruth Dodsworth
The Pollen Season
Running from March to the end of September, the pollen season is split into three main categories.
Tree Pollen - from late March to mid-May.
Grass Pollen - from mid-May to July
Weed Pollen - from the end of June to September
Pollen is a very fine powder produced by the male parts of trees, flowers, grasses, and weeds to fertilize other plants of the same species. Many people have an adverse immune response when they breathe in pollen.
The immune system normally defends the body against harmful invaders, such as viruses and bacteria, to ward off illnesses.
Some peoples immune system mistakenly identify harmless pollen as a threat to the body and tries to fight it by releasing a chemical. We call this an allergic reaction, which can lead to a number of irritating symptoms such as
The Pollen Count
A pollen count is generated by measuring the number of pollen grains in a given volume of air, using a pollen trap.
What effect does time of day and weather have on pollen count?
Pollen counts tend to be higher in the early morning and late evening, although they can sometimes be high all day long.
If the grass is damp, the pollen peak will be later in the morning because the water evaporates before the pollen is released.
Some grasses release their pollen in the afternoon. Pollen rises in the air during the day and then descends at night, as the air cools.
In rural areas, the evening peak tends to occur between 6pm and 9pm but in the city, where the air stays warmer for longer, the pollen descends later and levels tend to peak between 9pm and midnight or even later, which is why you may wake up sneezing in the night.
Sunny days favour higher pollen counts and rain tends to wash the pollen away. On a cloudy day, pollen builds up only to be released on the next sunny day.