STD Awareness: The Vaginal Microbiome and Cervical Cancer

Cervical cancer is caused by human papillomavirus (HPV), which has been nicknamed “the common cold of STDs” — because pretty much every sexually active person will get it at some point. Luckily, that scary stat is poised to change as more people receive the HPV vaccination, which protects against nine major strains of the virus.

HPV jumps easily from person to person, spread by pretty much all types of sexual contact. For most people, the infection clears up within 8 to 13 months, but sometimes the infection develops into a chronic condition, which increases risk for certain cancers — including cervical cancer, but also cancers of the anus, genitals, and throat. Unfortunately, it’s hard to predict if your immune system will vanquish your infection, or if you’ll develop a chronic infection.

Members of the lactobacilli family, keeping vaginas healthy across the globe. Image: Josef Reischig

Luckily, the vagina has some tricks up its sleeve to protect itself from HPV, and some of its best weapons are bacteria. Yep — a healthy vagina isn’t germ-free. To the contrary, it needs lactobacilli and other beneficial microbes to maintain a healthy environment. Bacteria from the Lactobacillus genus produce lactic acid and other chemicals, which help keep dangerous bugs away. Vaginal environments in which Lactobacillus gasseri dominate, for example, are more likely to clear HPV infections. L. crispatus helps trap HIV in a thick mucus, reducing infection risk. Other lactobacilli species secrete chemicals that ward off yeast infections. Sometimes, however, good bacteria lose this turf war, and “bad guys” move in.


The population of microbes that live in your vagina are known collectively as the vaginal microbiome.


University of Arizona researchers in Phoenix performed a “census” of the vaginal microbial communities of 100 premenopausal women. They learned that women who have cervical cancer or precancerous abnormalities have drastically different vaginal microbiomes. Healthy vaginas were generally dominated by lactobacilli, but as cervical health declined, their populations declined, and “bad” bacteria took over. One such bad guy, called Sneathia, was linked to HPV infection, precancer, and cervical cancer.

Which Came First?

Finding a new vaginal “bad guy” was exciting, and Sneathia had previously been linked to other gynecological problems, ranging from bacterial vaginosis to pregnancy complications. But the researchers were looking at a snapshot in time — they didn’t know what came first, the Sneathia or the cervical abnormalities. Were lactobacilli protecting the cervix whereas Sneathia were harming it, or did a chronic HPV infection set the stage for Sneathia to move in and thrive? It’s a real “chicken-and-egg” conundrum.

The order of events aren’t a mere curiosity — they have implications for our vaginal health. If Sneathia are merely the byproduct of an HPV-afflicted environment, getting rid of them wouldn’t get to the root of the problem — but they could at least be recognized as a warning sign that the cervix could be on the road to cancer. If, on the other hand, Sneathia boost an HPV infection and help it progress to cancer, then targeting those bacteria could weaken HPV’s foothold in the cervical environment, lowering cancer risk. Perhaps we could come up with strategies to create a vaginal environment in which lactobacilli flourished, which could create an acidic environment hostile to Sneathia. Many people find the idea of “probiotics” — beneficial bacteria — to be quite attractive, and hope that we could seed the vagina with beneficial lactobacilli species.

Unfortunately, we’re not there yet. Probiotic supplements and foods are available in stores, but we don’t have nearly enough evidence to know if they work as advertised. Yogurt, for example, contains lactobacilli and is often said to promote vaginal health. But it’s not made with the same lactobacilli species as those found in a healthy vagina. The most common Lactobacillus species in the vagina are L. crispatus, L. jensenii, L. gasseri, and L. iners, which are different from those found in yogurt, such as L. acidophilus and  L. casei. The species found in yogurt might not even be able to live in the vagina, let alone protect it.

A Healthy Vagina

A healthy vagina is pretty acidic, with a pH that typically maxes out at 4.5 — around the same level of acidity as tomato juice. Many harmful bacteria can’t survive in such an acidic environment, making lactobacilli and other beneficial bugs important friends of ours — and when they start dying off, the vaginal pH creeps up, giving “bad bugs” an opening. They’re able to move in, preventing “good bugs” from recovering and keeping pH relatively high, throwing the vaginal ecosystem into disarray. And as pH climbs, so too does the risk of cervical abnormalities.

As people with cervixes follow the path from HPV infection to cancer, their microbiomes become increasingly imbalanced. We might someday be able to look at a vagina’s microbial community and predict diseases like cancer. But it would be even better if reversing those microbial imbalances could also reverse disease progression — then we’d have strategies for prevention, not just prediction. Only time and more research will tell.

Right now, there’s a lot we don’t know about specific steps we can take to maintain healthy vaginal microbiomes, but there are a few tips we can offer, the most important of which is don’t douche — not even with plain water or vinegar. If you are sexually active, you can protect vaginal health by limiting sexual partners and using condoms during penis-in-vagina intercourse. You can also reduce your risk of HPV and associated cancers by being vaccinated with Gardasil 9, preferably before you become sexually active.

If you’d like more information on vaginal and cervical health or would like to get vaccinated for HPV, you can make an appointment at your local Planned Parenthood health center.


Click here to check out other installments of our monthly STD Awareness series!

2 thoughts on “STD Awareness: The Vaginal Microbiome and Cervical Cancer

    • I am not an official spokesperson for Planned Parenthood, but someone told me Planned Parenthood wanted to be in line with the CDC’s usage, and the CDC still uses STD. I’ve written about the differences in terminology here. There are pros and cons to each.

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