The healthy vaginal flora is made up of microorganisms such as lactobacillus jensenii and lactobacillus crispatus. In someone who has bacterial vaginosis however, the amount of lactobacillus will be reduced and this allows for the production of more unwanted bacteria such as Gardnerella vaginalis, Bacteroides, Mycoplasma and Mobiluncus and the further reduction of healthy bacteria. This is generally caused by rubbing and this is how it can happen as a result of sexual intercourse. Another common cause is the wearing of thongs which again rubs against the vagina and anus. This occurs mainly in sexually active women aged between 15 and 45, though it can also occur in pre-pubescent girls as a result of strep and improper hygiene following bowel movements.