Grass pollen, thunderstorms and asthma

It is difficult to visualize how pollen can trigger an attack of asthma, since airborne pollen grains are too large to be respirable. However, Pollen allergens, as distinct from the grains, are known to occur naturally in the environment associated with much smaller particles. How do these particles originate in the environment? This review addresses this question, in the light of new evidence. This has come from two sources: careful observations over 4 years of thunderstorm-associated epidemics of asthma in Melbourne and molecular cloning of rye-grass pollen allergens.