A new study says air currents in storms trigger asthma attacks - not electrical activity, rain or thunder as thought.
Downward draughts of cold air in the storm sweep up particles such as pollen and concentrate them in a narrow band of air close to the ground, called outflow.
People allergic to pollen and in the path of the outflow inhale air with super-concentrated levels of allergens, triggering an asthma attack.
The theory was advanced by researchers from the University of Sydney, Australia, who published their study in the journal Thorax.
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They studied airflow patterns and rates of hospital admissions for asthma during thunderstorms in six Australian towns between 1995 and 1998.
PA