#IfMenHadPeriods was trending on Twitter on Tuesday, and plenty of people were using it as an opportunity to call out sexism by highlighting how different the world would be if men had to deal with cramps and tampons and all that fun stuff. (Trolls also used it as a chance to mock women.) But the hashtag misses one very important detail: some men already do have periods.

Not all women have periods, and plenty of men do — as some folks on Twitter were quick to point out. To conflate menstruation with womanhood ignores trans men and agender or gender-neutral people, and pretty much anyone who menstruates and also doesn't identify as a woman.

The hashtag #IfMenHadPeriods has been around for a while — nonprofit WaterAid used it for a fake "manpons" commercial back in 2015. And the frame of critiquing institutional sexism by asking what the world would be like with male periods goes back at least as far as 1978, when Gloria Steinem's essay "If Men Could Menstruate" first appeared in Ms Magazine.

But menstruating men isn't a hypothetical situation for propping up an argument — it's a reality for many, many men. Steps towards inclusion in conversations about menstruation are happening in some places though — Planned Parenthood uses the gender-inclusive "menstruators" to refer to people with periods (which is apparently upsetting for people who insist that all women menstruate and no one else does).

But there are signs of inclusion in other places, too — like absorbent-period undies company Thinx, which changed their from "Underwear for women with periods" to "Underwear for people with periods" and ran an ad featuring trans model Sawyer Devuyst.

In a 2015 video for Thinx, Devuyst said, "Society has expectations of what a man is and what a woman is ... If you're not those two things, no one knows what to do with you."