People with asthma have been warned to keep their medications with them at all times this week because of the threat of summer thunderstorms.
Thunderstorms affect pollen exposure
At the end of June 2005 a six-fold rise in the number of emergency admissions for asthma was reported over one weekend as the result of thunderstorms.
It is thought the problem is triggered by the particular climatic conditions associated with summer storms.
This can make pollen - a known allergen - more of a risk than usual.
Professor Martyn Partridge, chief medical adviser to the charity Asthma UK, said it was important that all people with the condition made sure their medicines were readily available.
CONDITIONS THAT INCREASE THE RISK OF ATTACKS
High pollen counts
High levels of air pollution
Preceding dry spell of 5-7 days
Source: Met Office
He said "Thunderstorms occurring at a time when the pollen levels have been high have been associated with previous epidemics of asthma attacks.
"It is believed that the inversion of temperatures, that occurs at the time of thunderstorms, brings down pollen granules which the moisture then breaks up to a size that is breathed in to the lungs of those with asthma in large quantities, inducing attacks even in those who have only previously had mild asthma."
For years asthma sufferers claimed their condition worsened during thunderstorms, but there was little scientific evidence to back this up.
But the current theory was backed by an Australian study published in the journal Thorax in 2001.
The scientists found the hourly grass pollen counts recorded during a thunderstorm were up to 12 times higher than usual.
Further information is available from the the Asthma UK Adviceline on 08457 01 02 03.