For many people, spring is a double-edged sword. On one hand winter's over, but on the other that means the season of sniffles, sneezing and itchy eyes is upon us.
Hayfever is the body's response to airborne allergens like pollen and dust.
In some people, the immune system mistakes that stuff for harmful bugs and mounts an attack by releasing histamine into the bloodstream, which causes the allergy's dreaded symptoms.
Two hundred years ago, hayfever was largely unheard of. It was considered a freak disease of the rich that was associated with being in an overly clean environment.
These days it's more common in cities than rural areas, which some think is due to pollution from traffic and other sources acting as an additional irritant.
Experts don't know why some suffer from it and others don't, but they do know it's affecting more people than ever before.
Pollen seasons are also starting earlier and lasting longer, which some scientists attribute to climate change.