The air always seems fresher after a thunderstorm. Nevertheless, some people with asthma find their conditions get worse, not better, after a storm.
In high-profile examples, large numbers of asthma attacks followed storms in 1987 in Melbourne, Australia, and in 1994 in London. So what's the relationship?
A 1998 report in the International Archives of Allergy and Immunology explains that grass pollen is a common allergen that can trigger hay fever and asthma attacks. But grass pollen granules themselves are usually too large to find their way deep into the lungs, which could cause an even more severe attack.
It's only on exposure to water that the pollen grains break up. When this happens, each pollen granule releases as many as 700 starch particles. These particles contain the real allergen, and they're small enough to work their way deep into the lungs.
When it rains, it pours.
