Hay fever sufferers could be facing weeks of itchy eyes and sneezing, the Met office has warned.
High levels of pollen are expected across the Midlands and south of England, as well as in all of Wales and Northern Ireland until Friday, the weather service said.
The forecaster said the north east of England and Scotland will see low levels of pollen.
More people will begin to suffer from hay fever as the tree pollen season ends and transitions into the grass pollen season, the Met Office said.
Spokesman Grahame Madge told the PA news agency: “We are now getting into grass season. With it being so dry across the UK, it means grasses are able to shed pollen.
“For sufferers, hay fever has been a feature of the last few days and will continue to be a feature for sufferers over the next few days and weeks.
Doctor Milli Raizada, GP and senior clinical lecturer at Lancaster University, said students’ exam performances may be affected, especially when they are doing tests.
She told PA: “Exam performance can be affected when pollen levels are highest in the summer months.
“People think it is such a minor condition but it can have an impact on people’s work performance and sleep.
“I think there are lots of theories about why (hay fever) has been so bad. The prolonged cold weather and then the sudden explosion of warm weather has led to very high counts of pollen.”
She said antihistamines can be used as a preventative measure a couple of weeks before high pollen levels are expected.
People can also stay inside, keep windows closed and wear sunglasses to reduce the level of pollen they are exposed to, she said.