Among the 36 million people who experience migraines in the United States, the affliction is three to four times more common in women than in men.

It’s the reasons behind them that have a way of getting twisted.

Dr. MacGregor, who is also a neuroscience professor at Barts and The London School of Medicine and Dentistry, said that hormonal changes related to the menstrual cycle do play a role in migraines for some women and that migraines have been found to be more common in some women during their periods.

“Clearly this is not a relevant trigger for men!” she wrote in an email.

But excess emotions are not that trigger. Rather, it is a shift in hormones starting “a chain of events which activate neurons in specific parts of brain and send out signals which other parts of the brain interpret as pain,” she said. M.R.I. data backs this up.

Hormones are just one piece of the puzzle, said Tobias Kurth, an epidemiologist at Harvard who has investigated the potential dangers of overlooked migraines in women.

Lights, smells, alcohol, and certain foods are among the hundreds of environmental factors that can trigger migraines in people with genetic predispositions for them. At last count, variations of more than 40 genes were associated with migraines, according to David W. Dodick, the president of the International Headache Society. Research suggests that there’s a genetic component to at least 50 percent of migraine cases.