Some people get a headache before it rains. Is this real? Scientists in Japan looked at about 340,000 headache records from a phone app. There were more headaches when the air pressure was low or falling.

In an experiment with mice, a part of the inner ear seemed to sense changes in air pressure. But the weather does not affect everyone. Some people never get weather headaches.

Many people in Japan talk about "weather pain," such as headaches that come before rain. Research suggests this is not just imagination. In one study, 28 patients with migraine kept a headache diary for a year, and their records were compared with daily air pressure. Their headaches tended to increase when the pressure dropped sharply, and 18 of them showed a link to the weather.

A larger study analyzed about 340,000 records from a headache app and found more headaches during low or falling pressure, high humidity and rain. Why? An experiment with mice suggests that the inner ear, which controls balance, may sense pressure changes. However, results differ between studies, and many people are not affected at all.

Headaches blamed on the weather are often dismissed as imaginary, yet several studies point to a real association, at least for some people. In a Japanese study, 28 patients with migraine kept a headache diary for a year near a weather station in Utsunomiya. Migraines tended to increase when barometric pressure fell by more than 5 hectopascals from the day of a headache to the next day, and 18 of the 28 participants, or 64 percent, showed a link with weather changes.

Another study found that migraine was more likely when pressure was about 6 to 10 hectopascals below standard. On a much larger scale, an analysis of roughly 340,000 records from about 4,400 users of a headache app found more headaches during low or falling pressure, high humidity and rain.

A possible mechanism comes from mice: when pressure in their chamber was lowered by 40 hectopascals, neurons in the part of the brain that receives signals from the inner ear became more active. The evidence has gaps, though. International reviews describe inconsistent results, the mouse findings have not been fully confirmed in humans, and app users are not a representative sample. People may simply remember rainy-day headaches more vividly.