When is tree pollen season in the UK and what time of day has the highest pollen count? – The Sun

WARMER spring days are expected to trigger a spike in pollen counts meaning hay fever hell for the one in five Brits who experience seasonal allergies.

But the way different pollen types affect people can vary from person to person. Here's what you need to know about tree pollen season.

What is a tree pollen allergy?

Pollen from trees and shrubs can trigger hay fever, which is a type of allergy, sometimes called seasonal allergic rhinitis.

Hay fever occurs when your body makes the mistake of treating the tree pollen, or pollen from shrubs, as a harmful organism, and the immune system goes into action by making antibodies to try to prevent it spreading.

Symptoms of hay fever include sneezing, itchy, even watery, eyes and a stuffy nose, and about 1 in every 4 people in the UK who have hay fever are allergic to tree pollen.

Alcohol, including beer, wine and other spirits, worsens hay fever as they contain histamine – the chemical that sets off allergy symptoms in the body.

When is tree pollen season in the UK and when does it end?

The pollen season across the UK is separated into three main sections.

From late March to mid-May is tree pollen season, while mid-May to July is grass pollen season and weed pollen season runs from the end of June until September.

Tree pollen levels are expected to hit hard this week for all of the UK except Scotland and the far north of England, with the worst to come after Easter.

The tree pollen season this year is due to finish by mid-May, but it varies depending on where you live.

Around 20 per cent of hay fever sufferers are allergic to tree pollen.

The trees in the UK which are most likely cause problems are birch, alder, hazel and horse chesnut.

What time of the day has the highest pollen count?

A pollen count is generated by measuring the number of pollen grains in a given volume of air, using a pollen trap.

The threshold for 'high' pollen count depends on the type of pollen, but usually hay fever symptoms begin when the pollen count is 50 grains per cubic metre of air.

For grass pollen, a count between 50 to 150 pollen grains per cubic metre is considered high and for trees a count between 81 and 200 is high

Pollen counts tend to be higher in 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.

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, whereas on a cloudy day, pollen builds up only to be released on the next sunny day.

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