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Do You Know The State Of Your Vagina's Microbiome? Here's Why It Matters

Ina Park M.D., M.S.
February 8, 2021
Ina Park M.D., M.S.
Associate Professor & STD Prevention Consultant
By Ina Park M.D., M.S.
Associate Professor & STD Prevention Consultant
Ina Park, M.D., M.S., is an Associate Professor in the Department of Family and Community Medicine at UCSF, the Medical Director of the California Prevention Training Center and a Medical Consultant for the Division of STD Prevention at the CDC.
Image by mbc creative
February 8, 2021
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When things are going well in the vagina, millions of good bacteria (certain species of Lactobacillus) happily reside on the vaginal walls and within vaginal fluid. There they metabolize the sugar molecule glycogen inside the vaginal tissues, producing lactic acid as a result.

In a happy vagina, the lactic acid from Lactobacillus creates a pH between 3.5 and 4.5. This means vaginal fluid should taste slightly tangy but not sour: Think yogurt or merlot, not lemon juice.

Unlike the gut, where a wide diversity of bacteria is a plus, the optimal vaginal microbiome has almost all Lactobacillus and little else. There are dozens of other bacterial species that can potentially grow in the vagina, but ideally, the acidity of the environment keeps those bacteria under control. The acidic conditions also help protect against bacteria or viruses introduced by fingers and penises, including STIs and HIV.

What are the 5 vaginal community states?

Even though people are highly diverse in age, race/ethnicity, and sexual behavior, their vaginal microbiomes can typically be classified into one of five major categories, called vaginal community states 1 through 5.

These include optimal and less optimal environments for sexual and reproductive health. In the optimal community states (I, II, III, and V), Lactobacillus dominates, the pH is nicely acidic, and all is right with the world.

Community states on the other end of the spectrum are different. In community state IV, Lactobacillus may be present, but they are less plentiful, allowing the growth of diverse groups of bacteria who also thrive in the vagina's anaerobic environment. Gardnerella vaginalis is the best known among these, but there are dozens of others with names reminiscent of Cinderella's stepsisters: Prevotella, Sneathia, Eggerthella.

In less optimal community states, the vaginal pH is higher than the ideal range of 3.5 to 4.5 (closer to 5.5). These states would be present when women have the discharge and odor of bacterial vaginosis (BV).

Image by STRANGE BEDFELLOWS: Adventures in the Science, History and Surprising Secrets of STDs / Modified from S. Srinivasan et al. PLOS ONE, 2012.

Pictured above: Species of bacteria in the vaginal fluid of 220 women. Each woman is represented by a thin horizontal line, and more shades of gray represent a greater diversity of bacterial species.

Women with BV (microbiome often in community state IV) have more diverse bacteria compared to women without BV (microbiome often in community states I, II, III, and V).

However, less optimal states aren’t always associated with disease.

Researcher Jacques Ravel, Ph.D., found these community states in over a third of healthy Black and Hispanic women and almost 20% of Asian women, compared to less than 10% of white women. Notably, his team didn't actually ask women about symptoms, and they couldn't tell whether the differences in community state were related to genetics, personal habits, or sexual practices. While Lactobacillus-poor community states may be "normal" for some women, these women are more vulnerable to developing discharge and odor, plus other negative outcomes related to pregnancy and acquisition of STIs/HIV. 

Just like in any neighborhood, the vaginal bacterial community state can shift and change. Some vaginas stay in one state for weeks, while others can change dramatically over the course of a day. The monthly presence of menstrual blood (pH 7.4) causes everyone's vaginal microbiome to take a hit. Lactobacillus concentrations go down, and Gardnerella concentrations go up. Vaginal pH also takes a hit when semen enters the picture (pH 7.2–7.8).

Whether a vagina can bounce back to its optimal state and how quickly that happens will be different for every person.

Do you have a resilient vagina?

We all know people who are as stable as rocks: They lose their jobs, break up with their partners, and crash their cars, yet they remain steady and calm. (I am not one of these people, but I know they exist.) On the other hand, there are people who are barely holding it together, where you know any tiny stressor might just push them over the edge.

Vaginas are like this too. A resilient vagina can take multiple insults, and its microbiome quickly recovers to its usual state. However, for a fragile vagina, even a small insult like semen or menstrual blood can push it into a state of chaos. (Note that vaginal resilience does not appear to be related to emotional stability. You can be a hot mess and have a vagina of steel.)

Many forces can affect the resilience of the vagina, and one of the most powerful of these is estrogen. Lactobacillus thrive when estrogen is most plentiful, typically during the decades after puberty and before menopause. When perimenopause strikes, the roller coaster of waxing and waning estrogen levels doesn't just cause hot flashes and changes in bleeding. This hormonal instability can result in declines in Lactobacillus, placing a previously stable vagina in a more vulnerable state.

This isn't just a women's issue. When transgender men begin testosterone therapy, estrogen levels in the vagina plummet, and the vaginal microbiome transitions toward a menopausal state. So just when transgender men might be enjoying the masculinizing effects of testosterone, they may face more vaginal troubles than they did before they began their hormonal transition.

Once menopause has fully set in, the vaginal community changes yet again. Without estrogen, the vagina's surface thins out and becomes drier. Its tissues produce less glycogen, which means less food for Lactobacillus species. And it's not just Lactobacillus that moves out of the neighborhood—the BV-associated bacteria often do too. A vagina once crowded with bacterial inhabitants becomes more deserted after menopause.

How to balance the vaginal microbiome.

While the effects of menstruation, menopause, and hormones on the vagina are often outside of our control, we do have power over what we choose to put inside them. The only things that have any business inside the vagina are for pleasure or menstruation: fingers, sex toys, tampons/menstrual cups, or penises (one at a time is easiest).

Here's a good rule of thumb: If you wouldn't put it in your mouth, then don't put it in your vagina. (OK, no one actually puts clean tampons in their mouth, but you could.) Unfortunately, the converse isn't true. Keep that pizza out of your vagina, as it will wreak havoc on your microbiome.

These rules to live by seem simple, yet millions of us abuse our vaginas each year by exposing them to douches and other "feminine hygiene" products. This fixation with cleaning and perfuming our vaginas is certainly nothing new. Extreme vaginal hygiene has been a long-standing American pastime—one with surprising and sometimes disastrous consequences.

Excerpted and adapted from Strange Bedfellows: Adventures in the Science, History, and Surprising Secrets of STDs by Ina Park. Copyright © 2021 by Ina Park. Reprinted with permission from Flatiron Books. All rights reserved.
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Ina Park M.D., M.S. author page.
Ina Park M.D., M.S.
Associate Professor & STD Prevention Consultant

Ina Park M.D., M.S., is an associate professor at the University of California San Francisco School of Medicine, Medical Consultant at the Centers for Disease Control and Prevention, Division of STD Prevention, and Medical Director of the California Prevention Training Center. She holds degrees from the University of California Berkeley, UCLA School of Medicine, and the University of Minnesota School of Public Health. Recently, Park served as a co-author of the 2020 CDC STD Treatment Guidelines and contributor to the Department of Health and Human Services STI Federal Action Plan. A fierce advocate for public health, she lives in Berkeley, CA with her husband and two sons.