Pollen can trigger allergic reactions, including hay fever and can make conditions such as asthma worse.
The amount and type of pollen in the air depends on the time of year and place. Hay fever is usually caused by grass pollens during late spring and early summer.
The UK Met Office provides updates on the pollen count with a pollen forecast. It is good to get to know what levels may affect you.
Thunderstorms may also trigger asthma. This is because of humid air combining with pollen being blown around.