At sufficiently acidic pH, lactic acid acts as a potent microbicide. Lactic acid produced by vaginal lactobacilli may have a role in protecting against reproductive tract infections. Lactobacilli are known to acidify the vagina with lactic acid. During episodes of bacterial vaginosis (BV), lactobacilli and vaginal lactic acid have been found to be considerably reduced.1

Additionally, lactic acid is known to inactivate an array of reproductive tract pathogens, including HSV-2, Neisseria gonorrhoeae, and Escherichia coli.1

A low and acidic pH is key to maintaining a healthy vaginal microflora. Most lactobacilli flourish at a pH < 4.5. The ideal pH of women of reproductive age is 3.5-4.5. This is attained with the presence of a sufficient amount of lactic acid in the vagina. Therefore, lactic acid is essential for maintaining a medium which facilitates the growth of lactobacilli in the vagina.2

Furthermore, the lactic acid compound produces hydrogen peroxide and favors the action of bacteriocins, which is harmful for a wide range of pathogens.2

In candidal vulvovaginitis, BV, or nonspecific vaginitis, the treatment should focus on two key aspects - decrease in the pathogen quantity and recovery of the vaginal pH. In order to prevent relapse, it is important to recover the vaginal pH.2 Therefore, formulations that can help with the recovery of the lactobacilli population need to be given along with antifungals or antibiotics in vaginal infections.

Providing lactic acid to the vagina does away with the need to depend on the actions of the exogenous probiotics administered. Therefore, the appropriate treatment of vaginitis involves the administration of an antifungal or an antibiotic followed by acidifying the vagina with lactic acid.2

A study investigated the effect of treatment of BV with high dose vaginal metronidazole and followed by vaginal application of lactic acid in some patients. In all, 45 patients with BV were divided into 3 groups. The first group comprised of 18 women who were given vaginal suppositories of metronidazole; in the second group, 20 women received metronidazole and a following therapy with lactic acid. The third group (7 women) was the control group that received placebo. In the metronidazole group, there was normalization of vaginal flora in 71.43%, intermediate vaginal flora in 14.3% and no change with therapy in 14.3%. In the second group, 94.1% patients were cured and only one (5.9%) case revealed intermediate vaginal flora. In the control group, in 85.7% of the cases there was a lack of effect. Therefore, treatment with metronidazole showed favorable results in 71% of cases while addition of lactic acid improved the therapeutic effect and cure was achieved in about 94% of the cases.3

In another study, researchers assessed the recurrence of BV after the use of a lactic acid plus lactoserum product immediately after treatment with oral metronidazole. The lactic acid plus lactoserum product for external intimate hygiene was found to be a potential option for the prevention of BV recurrence after treatment and cure with oral metronidazole.4

Application of vaginal lactic acid thus seems beneficial in maintaining the ideal vaginal pH and preventing BV recurrence.

References

1. O’Hanlon DE, Moench TR, Cone RA. Vaginal pH and Microbicidal Lactic Acid When Lactobacilli Dominate the Microbiota. PLoS One. 2013; 8(11): e80074.
2. Haya J, García A, López-Manzanara C, et al. Importance of Lactic Acid in Maintaining Vaginal Health: A Review of Vaginitis and Vaginosis Etiopathogenic Bases and a Proposal for a New Treatment. Open Journal of Obstetrics and Gynecology 2014;4:787-99.
3. Andreeva P, Slavchev B, Kovachev SM, et al. Treatment of bacterial vaginosis with high dosage metronidazole and lactic acid. Akusherstvo i ginekologiia 2002;41(5):36-9.
4. Bahamondes MV, Portugal PM, Brolazo EM, et al. Use of a lactic acid plus lactoserum intimate liquid soap for external hygiene in the prevention of bacterial vaginosis recurrence after metronidazole oral treatment. Rev Assoc Med Bras 2011;57(4).