Although there is limited research into yogurt's relationship to vaginal health, eating yogurt or inserting it into the vagina is a popular folk remedy for vaginal infections. The cultures in yogurt probably help prevent and treat vaginal infections caused by bacteria, but there's not enough evidence to suggest they help with yeast infections.
Yogurt is rich in healthful bacteria, or live cultures, called probiotics. Bacteria in the Lactobacillus family are found naturally in the vagina, so many of the studies of probiotics and vaginal health have focused on Lactobacilli. Additionally, most of the studies on vaginal health and probiotics have focused on the cultures rather than yogurt, per se.
Most women have candidiasis, or yeast infection, of the vulva or vagina at least once, according to the National Institutes of Health's Medline Plus. A yeast infection is an overgrowth of a fungus, usually Candida albicans, normally found in small amounts in the vagina. Yeast infections are usually treated with over-the-counter antifungal creams or suppositories. Some women battle recurring yeast infections. The "Journal of Family Practice" reported that existing studies don't support using yogurt or suppositories containing Lactobacillus to prevent recurrences of vaginal yeast infections; however, Medline Plus does recommend eating yogurt or taking probiotic supplements if you are on antibiotics, since taking antibiotics increases the risk of yeast infections.
Bacterial vaginosis is a common infection in women of childbearing age, according to the Centers for Disease Control and Prevention. It frequently affects pregnant women, who are more likely to have premature or lower-weight babies if infected. It occurs when Lactobacilli, or good bacteria, are overrun by bad bacteria in the vagina. It is usually treated with antibiotics, but often recurs after treatment. In a review published in the "Journal of Lower Genital Tract Disease," researchers noted that most studies have shown that eating probiotic-rich foods or applying probiotics topically may help prevent or treat bacterial vaginosis.
While yogurt may not help prevent or treat all types of vaginal infections, it probably won't hurt. The "Journal of Family Practice" points out that neither eating yogurt nor using probiotic suppositories has been shown to have any significant adverse side effects. Based on studies, Columbia University's GoAskAlice.org recommends eating 8 ounces of yogurt daily, taking probiotic supplements or administering about 1 tablespoon of yogurt to the vagina. Use plain yogurt since sugar can encourage the growth of yeast.