Nine out of ten were women

In the largest Japanese dataset, 89% of users were women. That's not a bias in the app. It's a bias in the disease.

89.2%. In the largest dataset in this overview — 4,375 users of a Japanese headache app, 336,951 hourly logs of headache and weather over a full year — more than eight out of ten users were women. That's not a coincidence, and it recurs almost everywhere you look.

Three datasets, same pattern

The Japanese app study landed on 89.2% women (3,902 of 4,375). When 13,207 Britons downloaded a similar app to log weather and pain, 81% of them were women. And when a systematic review in 2025 gathered 2,696 participants from 14 studies of air pressure and migraine across half a century of research, the share was 87.9%. Three different countries, three different methods, three figures that sit closer together than you'd expect.

Half the explanation: who has the disease

The most obvious explanation is the right one: migraine affects far more women than men. A Danish follow-up study found a migraine incidence of 8.1 new cases per 1,000 person-years — with a ratio between men and women of 1:6. Another Danish population study found a lifetime prevalence of 8% among men and 25% among women. Looking only at who has the condition at all, a skew towards women is built into the figures long before anyone has downloaded an app.

The other half: who signs up

But a rough calculation on 8% against 25% would put women at around three-quarters of a migraine population, if both sexes logged equally eagerly. The actual figures in the app studies — 81 to 89% — sit well above that. Some of the difference comes from the studies not being about migraine alone: the British dataset also counted arthritis, rheumatoid arthritis and fibromyalgia, all of which also affect more women than men. But some of the difference also points to women not just having the condition more often — they also sign up more often to spend time logging it.

Women also identify as weather-sensitive more often

The same picture recurs outside patient groups. In a German population survey, run regularly since the 1950s, a fixed share of the population reports that weather affects their health — and women are more often affected than men, according to the survey itself. Headache and migraine are, moreover, by far the most common symptom among those who consider themselves weather-sensitive at all. It's not only a question of diagnosis. It's also a question of who notices the link and chooses to do something about it.

The 2025 review itself names the skewed sex distribution as one of the literature's weaknesses — small samples skewed towards women make it harder to say anything general about men. That's a fair objection. It doesn't change the fact that the skew is real, consistent, and too large to be coincidence.