Pollen levels are on the rise just one week after the spring equinox, the Met Office has reported.
Tree pollen is set to be moderate to high over the coming days across some southern parts of England and Wales.
Hay fever sufferers may start to experience more symptoms than usual as the pollen count rises over the next five days, with tree pollen affecting around a quarter of people, according to the forecaster.
London and the south east of England saw high ash pollen levels on Saturday, while the south west experienced moderate levels.
As of Monday, both regions will see high ash pollen counts, with levels also rising across the Midlands. Wales, the midlands, and the east of England will all see moderate pollen levels while counts will remain low for the rest of the United Kingdom.
On Tuesday, Grampian will see moderate pollen levels while the rest of Scotland and the north of England will see relatively low counts.
Pollen levels will remain high across the midlands, east, south east and south west of England on Wednesday while Wales will only see moderate levels.
The forecaster has warned birch pollen season will also start soon. Birch pollen occurs between March and June, peaking between April and May, and can cause asthma and rhinoconjunctivitis (irritated eyes, nose and sinuses).
It is estimated that around 10 million people in England suffer from hay fever. Symptoms usually appear when the pollen count, a measure of the number of grains of pollen in one cubic metre of air, exceeds 50.
The weather conditions affect how much pollen is released and spread around, according to the Met Office, who said it was more prevalent on humid and windy days.
Temperatures look set to stabilise above 10C for most of the country next week, according to the forecaster, who predicted bright spells for parts of the country. On Tuesday, temperatures will enter the mid teens for most of the UK with bright conditions and a bit of cloud.
Met Office five day forecast
This evening and tonight:
Daytime showers largely easing during this evening with most places becoming dry with clear spells. A band of cloud and rain though will arrive into Scotland and Northern Ireland later. Turning cold with a widespread slight frost.
Sunday:
A chilly and bright start across the southeast, but cloud and rain already in the northwest will spread across the country. Brighter but showery conditions following behind, but remaining blustery.
Outlook for Monday to Wednesday:
Remaining cool but drier on Monday. Warmer on Tuesday with bright spells, but also some patchy rain in the west. Further rain in the northwest Wednesday but some brightness elsewhere.
