As someone who worked in retail for a while, it's very common to find women buying yeast infection medication and douche kits in the same transaction. It took all the will-power I had to not cry out "What are you doing??? Do you not see the cause and effect right there on the counter???"
As many have said already, the vagina is a self-cleaning orifice. (Would you douche your urethra? Hell no!) There are "good" bacteria in the mucosal membrane that maintains the pH balance and healthy environment. By douching, you risk killing off good bacteria that would otherwise protect you from infection and at the same time it forces foreign bacteria up further into the vaginal canal, possibly even into the uterus, causing infections or worse! And since most women douche for smell reasons, it's interesting to note that infections cause more terrible odor than what you started with!!!
Also worth knowing is that you should never, ever, ever use soap
inside your vagina. You can wash the labia and external vulva that way but don't insert it. It's no better than douching. Just don't. Also, don't force water up into it either. Yeah, same thing. Just washing the outside well, let it dry, change your underwear, don't wear pads or tampons too long, and see a doctor when necessary. Seriously.
This has been a PSA by Darling Jen.