How does weather affect hay fever?

While others are quick to head to the park on a sunny day, hay fever sufferers are likely to want to hide inside. This is because warm, dry, sunny days during the summer months commonly lead to high pollen counts.

The UK’s pollen season generally starts in March.² But, depending on where you live in the UK, the season may start at different times. Warmer, sunny weather brings higher levels of tree and grass pollens.

When temperatures rise above 13°C, the warmth causes trees to release pollen.³

According to the Met Office, trees respond best to a temperature range of between 13-15 °C. However, pollen levels will decrease if temperatures rise above 28 °C. If the weather is very hot for several days in a row, then pollen may not be present at all.⁴

Rainfall causes a decrease in pollen concentration, as moisture weighs down pollen, keeping it on the ground. Rain also suppresses pollen transportation and clears the air.

But the time and amount that it rains during the day can make a big difference. Heavy, prolonged, early morning rain is likely to keep pollen counts low all day, while rain in the afternoon will have less of an impact.⁴

Rain doesn’t always signify the end of hay fever symptoms, though. Intense summer thunderstorms typically occur after a period of dry weather, during which pollen accumulates on the ground. The storms stir up pollen and pollution particles in the air, which can increase pollen levels and trigger hay fever.

If rain also occurs at the same time, then the humidity in the air can rupture dry grass pollen grains, releasing clouds of tiny, allergy-triggering fragments into the surrounding air.⁵

Summer thunderstorms can produce ‘Thunderstorm asthma’ – a phenomenon where people with  hay fever also get symptoms of asthma, as part of their allergic reaction to pollen.

Wind transports pollen around and can carry it long distances, potentially hundreds of miles. However, it all depends on wind strength – the Met Office says that if wind is too light, pollen will not get off the ground to be dispersed, and if it’s too windy, it can thin out considerably. Different types of pollen require different wind speeds for dispersion.⁴

Time of day is also an important factor in hay fever. Plants start to release pollen early in the morning and, as the day gets warmer and more flowers open, pollen levels increase. Rising hot air carries pollen alongside it, which then drifts back down on the cooler evening air.

This explains why symptoms can be troublesome mid-day, and why in the middle of a hot night, you can get an attack of hay fever, particularly if you sleep with your bedroom windows open, even though the plants that produce pollen have shut for the night.

•spring – Plants start to release pollen in February or March. Tree pollens are also a common  spring allergen.

•summer – Early in summer, grass pollen can trigger reactions. Later in the summer, weed pollen such as ragweed can become a problem.

•autumn – Ragweed season usually ends with the first frost in October.

•winter – Indoor allergens – like pet dander and dust mites – can produce symptoms in winter, but less pollen allergens are present.

•Get ahead of your allergy.  If you find you get the same allergy symptoms at the same time every year – grass pollen in the summer, for example – then start preparing early. Ask your GP if you can take allergy treatments about two weeks before you usually start seasonal sneezing, coughing, or itching. That way, you can prevent symptoms before they start.

•Watch the weather.  Check local pollen counts, watch for Ozone Action Days, and spend less time outdoors when peak pollination is likely to cause an increase in symptoms.

•Control your environment.  You can't change what's happening outside, but you do have some control over your indoor environment. Use an air purifier to trap pollen and other microscopic particles and dust.

•Wash away allergens. Pollen can collect on your skin, hair, clothes, footwear and pets.⁶ After you’ve been outdoors, aim to wash your clothes as soon as you take them off, and shower to wash away pollen particles.

•Prevent pollen entering your home. Keep windows closed as much as possible to prevent pollen from drifting inside. Consider drying clothes indoors rather than in the garden, as pollen can stick to sheets and towels.

Pollen gets everywhere, indoors and outdoors. It can travel long distances and is hard to avoid completely. But taking simple steps to reduce exposure and staying up to date with weather forecasts and pollen counts can help keep hay fever symptoms under control.