Anyone who’s ever tried on a shirt made for the opposite gender has likely noticed the awkwardness of buttoning it up. This is simply because men’s shirts have their buttons on the right side while women’s have them on the left. But why?

Buttons have been used as fasteners for as long as 800 years, and while we take them for granted every day, most of us don’t question how the button gender-divide came to be. For men, the typical guess is that their clothing has buttons on the left side because it makes it easier for right-handed people to fasten them. Historically, there is likely more to it. Gentlemen of previous centuries traditionally carried swords and, most men being right-handed, carried them on the left so as to draw and wield them with the right hand. Having buttons on the right side made it easier to unbutton them with the left hand, as well as help prevent the swords catching on the open flap.

Note, for example, how portraits of Napoleon traditionally depict him slipping his hand into his coat, right-to-left. Illustrating the contrary is the case of orthodox Jews who weren't allowed to carry weapons, and to this day some of the jackets orthodox men wear will button on the opposite side. So in the case of men, weaponry would seem to be the root cause behind the button bias.

What about women? The most likely answer goes back to about the 17th century when women of the upper classes normally had maids to dress them in their elaborately fastened layers of garments. Most servants being right handed, buttons were placed on the left side to make dressing their mistresses easier. Maids themselves would not have had buttons on their garments, as they were a relatively expensive detail in pre-industrial times. It would seem that this tendency came down to us habitually, especially as historically the upper classes have largely dictated fashion trends. There are still more theories, one being that right-hand women tend to hold their infants in their left arms, so garments with open flaps on the right would be more accommodating to breastfeeding. Another is that because women rode horses sidesaddle to the right, putting their buttons on the left reduced the influx of wind into their shirts. Yet another is that because early industrialization coincided with the fledgling women’s movement, manufacturers used buttons to further emphasize gender, thus making it more of a statement. In any case, once buttons became easier to manufacture and apply to clothing, the predilection became the norm.

In our own times, some designers have occasionally reversed button sides just to make their own playful statement. Then there’s the zipper, which perhaps because it was introduced much later, is known to swing both ways. So if you wish to unbutton yourself from gender-norm constraints, you may just want to zip up instead.