It's summer here 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.
Hay fever is one of the most common allergies and affects around 13 million people in the UK.
You can get it at any age, although it usually starts when you are young.
Not everyone has hay fever, but is it more common in people whose family members already have it, or other allergies, especially asthma.
Although there is no cure for hay fever, people who have it can manage the symptoms in lots of different ways.
Special medicine called antihistamines or steroids are sometimes used to help prevent a reaction and reduce the swelling.
Top tips also include avoiding freshly cut grass, changing you clothes if you have been outside, and closing your windows at night-time.
However, it is always best to talk to a doctor about what is right for you, if you think you might have hay fever.
People can be affected by different types of pollen as well.
For example there is lots of tree pollen in spring, grass pollen in summer and weed pollen in the autumn.
People with hay fever can also keep an eye on how high the levels of pollen in the air are, by watching special weather reports.
As well as telling the weather, presenters can also give a pollen count, to warn people when the levels are high.