If you're reading this and you have breasts, take a moment to reminisce about the times you've stashed something in your bra. You might not be able to remember them all. On good days, pulling a $20 bill out of the depths of your cleavage makes you feel like a saucy broad in a classic film, and on bad days whatever you're stashing in there just feels pokey and weird. But, listen: Women don't pay for lunch with sweaty credit cards out of their shirts because it's fun; it's because they lack options. Since the pockets in many women's garments are either pathetically shallow or just missing (or fakes!), what's a woman of property to do when she's trying to go for a jog and has both keys and a phone to contend with?
She sticks them in the next best thing to a pocket, which is her sports bra. So, rather than wondering why a woman stores things in her bra, instead, maybe we should be asking what drove her to do it.
Believe it or not, the garment industry has a long history of keeping a woman and the places she might reasonably stash her belongings asunder.
Back in Medieval Europe, before pockets even existed, both men and women wore Ye Olde Fanny Packs, little bags on strings tied around the waist, allowing both genders an equal playing field when it came to accessing their stuff. By the 17th century, men's coats and trousers had pockets, but women still kept their sewing supplies, money, snacks, cosmetics, spectacles, keys, stationary, etc. in bags, tied around their waists under their skirts, between layers of petticoats. Some skirts had slits in strategic seams, handy for accessing these bags, but even if a woman was obliged to excuse herself in order to fish enough money out of her underwear to pay for a cab, hey — at least she had a place to keep it. After the French Revolution, dress silhouettes got much narrower, which heralded the advent of the dreaded reticule, or tiny purse. They were a lot like the modern clutch: unreasonably small, decorative, and impossible to locate after they've been put down somewhere.
And from then on, the patriarchy had women right where it wanted them: unable to fashionably carry anything, even money. Leave money-carrying to the men and their copious pockets.
By the turn of the 20th century, western fashion granted a man about 15 pockets in a single set of clothes, and women zero. During the following century, women all over the world gained more rights at home, in the workplace, as citizens, and in some places, societies loosened up, sartorially speaking. Women wear pants now, after all! But since slim silhouettes are pretty much always in style for women, fashion still hasn't granted them pockets. This is frustrating on a social and political level, of course, but the practical fact remains that it's tough to stash that gargantuan smartphone in your yoga pants or skinny jeans. Women have gained a lot of social traction over the millennia, but that doesn't mean they've got jogging shorts with nice, deep pockets in them. Yet.
Which is why women put their phones in their bras with such frequency that there are companies that have started fitting them with pockets. Necessity is the mother of invention, after all.