After record pollen levels last month, the British Allergy Foundation said the estimated 12 million people suffering from the condition should visit a doctor at least once a year. There is mounting evidence of a link between allergies and asthma.
A survey of 2,000 hay fever sufferers has revealed that two-thirds of people with the condition have not visited their GP recently. A spokeswoman for the foundation said: "If they don't have their symptoms properly reviewed, they have an increased risk of developing asthma."
The warning comes after the pollen count rose to its highest level in 12 years in June, leaving a record number of people with red eyes, runny noses and headaches.
The National Pollen Research Unit said yesterday pollen counts would remain high over the weekend, although conditions in the South will not be as bad as they were last month, when levels peaked.
"The pollen count is going to be high all weekend, especially in the North and the Midlands where counts tend to peak later in the summer than they do in the South," a spokeswoman said.
Hay fever experts are warning sufferers to stay away from the countryside on high pollen-count days, especially in the evening, when pollen descends. Other tips for preventing an outbreak include closing bedroom windows in the evening, keeping car windows shut and placing a filter over air inlets in cars.
The sunny spell enjoyed by much of the country will continue until the middle of next week, the Met Office said yesterday. A forecaster said temperatures over the weekend could reach highs of 27C (81F). "Parts of Northern Ireland and western Scotland will be cloudy with some rain, but further south it will generally be hot and sunny although there will be some cloud," he said. As thousands headed to the coast to enjoy the sunshine yesterday, four doctors at Bristol University denied they had been irresponsible by suggesting the benefits of sunlight could outweigh the risks.
Dr David Gunnell, who argued in an article in the British Medical Journal that the chances of dying from skin cancer caused by too much sun were slight, stressed that people should avoid excessive exposure to the sun.
He said yesterday: "What we have said is we need to carefully balance up the benefits and disbenefits of sunlight exposure. What is important is not to lose sight of the message that rates of skin cancer are rising and sunlight plays a role in that, but at the same time there may be some beneficial effects of exposure to sunlight."
Health campaigners said the article could undermine years of public health work aimed at convincing people of the dangers of too much sun.