Vaginal yeast infections (candidiasis) are infections of the vagina and vulva that cause discharge, irritation, and itchiness. A healthy vagina contains a normal balance of yeast and bacteria (lactobacillus). A yeast infection occurs when there is an imbalance of yeast. Most yeast infections are caused by an overgrowth of the fungus Candida albicans, though there are other types of candida fungus that need therapies that are more aggressive and are harder to treat. Yeast infections are not sexually transmitted infections, though you can get a yeast infection from your sexual partner because of a bad reaction to their natural genital yeast and bacteria.