Humans have known for many years that a variety of seizures known as catamenial seizures occur purely in women as a result of variations in sex hormones during the menstrual cycle. It turns out that the various hormones that circulate and alter throughout our reproductive cycle, with its typical 28-day run, can set up conditions in the brain that suppress or encourage seizures in women with epilepsy. Summarizing decades of study into the problem in 2015, scientists wrote in Seizure that "progesterone and its metabolites are anticonvulsant, while estrogens are mainly proconvulsant. The monthly fluctuations in hormone levels of estrogen and progesterone are the basis for catamenial epilepsy."

If you remember your basics about how estrogen and progesterone fluctuate during the menstrual cycle, you'll be able to track how catamenial seizures are influenced by them. Seizures can occur at the stage just before a period because the levels of progesterone, with its anticonvulsant properties, have dropped in the brain; they can also spike during ovulation, when estrogen levels peak, according to these scientists. It's not as simple as saying that these hormones "set off" seizures. It's more correct to think of it as excitability: these hormones either speed up or slow down certain aspects of brain activity, meaning that they might dampen or hasten seizure conditions. This isn't universal to all women, though: Some epileptic women will see very little effect from their hormones at all.

Unsurprisingly, this interaction between hormones and seizures means that, for some women, periods of huge hormonal fluctuation like the beginning of puberty and menopause can be rough. Going through puberty can mean seizures change or develop new patterns, while research in 2005 noted that 40 percent of women going through menopause said their seizure disorder worsened and 27 percent said it improved.