During the last few decades, a huge epidemiological effort has been made all over the world in order to cast some light on the origin of asthma (or ‘wheezing disorders’ as a general term) and its recent increase in prevalence. The focus on genetic factors has failed to show any genetic signal strong enough to be seriously considered, and the tiny genetic signals found have never been appropriately replicated. The focus on environmental factors has provided some variable signals on the role of infections, allergens and bacterial substances, the direction of which have curiously varied from protecting to inducing asthma. The only environmental factor that has launched a large and consistent epidemiological signal, found in almost every epidemiological study addressing the issue, is previous acetaminophen exposure, which consistently increases the prevalence and clinical manifestations of every wheezing disorder under study. Is acetaminophen a real asthma promoter or an innocent bystander?