A growing number of studies show that regular use of acetaminophen (paracetamol) carries a dose-dependent risk of developing allergies in general and asthma in particular and of worsening other respiratory diseases and lung function. The most disturbing finding has come from the population-based Avon Longitudinal Study of Parents and Children, in which use of paracetamol-but not aspirin-in late pregnancy was positively associated with asthma when comparing children whose mothers took paracetamol "sometimes" and "most days/daily" with those whose mothers never took it. Assuming a causal relationship, the percentage of asthma attributable to paracetamol use in late pregnancy was 7%. In this review, we present data from the most important studies published since 2000. Although the pathophysiology remains unclear, the available data justify a warning to the general public that the uncritical use of over-the-counter acetaminophen can lead to the development of allergies and asthma, even in utero.