From pollen count to pollen potency: the molecular era of aerobiology.

In 1873, Charles Harrison Blackley recognised pollen as the cause of hay fever and ‘‘hay asthma’’ [1]. For the first time, he collected pollen grains with a kite that had a sticky tail and then he counted them. Being affected by seasonal asthma himself, he also performed the first skin prick test on his own arm. Since then, aerobiology (from Greek á r, aēr, ‘‘air’’; bioz, bios, ‘‘life’’; and -locı́a, -logia), a branch of biology that studies airborne organic particles, including pollen grains and fungal spores, has played a key role in the study of the relationship between allergic diseases and pollen. Although thousands of experimental studies have supported the role of pollen in the pathogenesis of allergic rhinitis, asthma and conjunctivitis, data from epidemiological studies were controversial in many cases, casting doubt on the pollen count (i.e. the number of pollen of the same type per cubic metre of air) as a reliable proxy of allergen exposure.