It’s never necessary to douche. Vaginas are designed to be self-cleaning and douching can throw off the healthy environment, which can lead to increased risk for STDs or other vaginal infections. For this reason, vaginal douching is discouraged. Some people who have receptive anal sex (i.e "bottom" or have someone else's penis in their butt) douche before anal sex so that sex is not messy. Douching is a personal choice. It is most important to avoid injury to the anal/rectal tissue to reduce the risk of STDs.