Female sex hormones seem to have something to do with asthma and allergy. You might think this is a bit vague, but the research on this so far doesn’t merit anything stronger. Women of reproductive age are more likely to be admitted to hospital for asthma than men.1 Intrigued by this, people have studied the link between asthma or allergy and markers of female sex hormone levels—for example, time of menstrual cycle, menopause, pregnancy, hormonal contraceptives, hormone replacement therapy, maternal parity, and age at menarche—but the overall picture remains confused. The results of the studies are inconsistent, with no unifying pattern of effects of hormones. Three recent studies in Thorax, two in this issue2,3 and one published in June this year,4 have added some new pieces to the jigsaw puzzle and a new perspective on the problem.