Thunderstorms begin as little fair-weather clouds that usually form and disappear without producing rain or electrical effects. When the air is thermally unstable, a few of these clouds undergo a rapid change: they increase in height and rain and electric fields appear.
Thunderstorm asthma is caused by large amounts of whole pollen grains being pulled up into the clouds of an evolving thunderstorm. Small pollen allergen particles are released into the air in the cold dry outflows from the storm and arrive at ground level where they are breathed into people’s lungs.