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 issue^2,3 and one published in June this year,⁴ have added some new pieces to the jigsaw puzzle and a new perspective on the problem.

Brenner et al² looked at menstrual variation in asthma symptoms. We have recognised for a long time that some women get worse asthma symptoms at certain times of the month. Surveys of asthma outpatient clinics suggest that about a third of women experience worse symptoms just before and during their periods,^5–7 although the figure would probably be lower in community based surveys. A few researchers have shown that peak expiratory flows^5,6 or bronchial responsiveness⁸ vary over the menstrual cycle, but others have shown no such variation.^9,10 As with the premenstrual syndrome, exactly what it is about the different phases of the menstrual cycle that …