It's a warning not to be sniffed at.
Number-crunching allergy specialists have created a special formula to pinpoint the peak date and time for seasonal sneezing, runny noses and itchy eyes.
Red letter day for hay fever sufferers in the Midlands - a national hot spot for pollen-induced misery - has been calculated at 6.02pm on Monday May 29. It has been worked out using factors such as time of day, stage of the grass pollen release process, hours of activity outdoors, and rainfall.
Dr Adrian Morris, an allergy specialist and a GP with 20 years experience, said the Midlands was the worst
place for hay fever in the country, with Scotland being the least badly affected.
The formula was created by Dr Morris for Boots Health Club using data produced by the National Pollen and Aerobiology Research Unit at the University of Worcester.
The model for the formula is: T+S+(HxO) divided by R, where T is the time of day, H the hours of activity, S the stage of the grass hay fever season, O being outdoors and R is the amount of rainfall.
"The worst time of day for hay fever is three hours before sunset as this is when pollen released into the atmosphere in the morning returns to the ground and when many sufferers believe the worst of the day is over," said Dr Morris. Sunset on May 29 is just after 9pm.
Grass hay fever season has already begun to affect sensitive sufferers and reaches its zenith in late June, but Dr Morris predicts that people will experience the worst effects at the end of May because most sufferers do not medicate until after symptoms have begun.
A total of 20 per cent of the British population suffers from hay fever and of those 95 per cent are allergic to grass pollen, which is emitted until the end of July.
"The first peak of pollen catches so many people out," said Dr Morris, also an adviser to the World Allergy Organisation.
"As May 29 is a Bank Holiday many more sufferers than usual will be out and about, breathing in pollen.
"People will be mowing lawns, visiting garden centres, going to parks, having barbecues and the like, hugely increasing their exposure to pollen", said Dr Morris.
The worst weather for hay fever sufferers, he said, is when it is warm, dry and there is a light wind - this means maximum spread for the pollen particles. Rain aids hay fever sufferers by literally dampening down the pollen released each morning.
The Midlands is the worst place in Britain to be during hay fever season because the weather in the region is often favourable for good grass growth and for pollen dispersal.
There are also a lot of pastures, meadows, verges with a wide range of grasses flowering in them. Because the region is inland, the wind brings pollen to it from many directions.
Spring coming late this year has also caused several types of pollen to be released at the same time, which could be the reason some sufferers are reporting an early onset of their symptoms.
According to Dr Matt Smith, a researcher at Worcester University's National Pollen and Aerobiology Research Unit, this year's birch pollen count is higher than usual, and 25 per cent of hay fever sufferers are allergic to birch pollen.
The unit has been inundated with samples of yellow pollen which has reportedly travelled from birch trees in Scandinavia, collected by the public after settling on cars and property across the UK.
"In Scandinavia the birch pollen count has been three times as high as usual and this cloud has got together and deposited pollen in parts of the UK," said Dr Smith.
"We are studying samples sent in to us to see what the effect might be."