What is Hay fever? - and how does it affect people?
21 June 2017 Last updated at 07:20 BST
It's summer in the UK, and whilst that means lots of warm and sunny weather, it also can mean that people with hay fever might have a hard time.
Hay fever is an allergy - and people who have it are allergic to pollen.
Pollen is a type of fine powder which is released by lots of different plants and trees.
It has proteins in it which can cause your nose, eyes and throat to become swollen or irritated.
This means people can suffer from symptoms like itchy eyes or runny noses as your body tries to protect itself from the pollen by flushing it out.
Hayley has been finding out some top advice on how to help manage these symptoms, and beat the hay fever blues!