What is bacterial vaginosis? Causes and symptoms to look out for

    Updated 19 January 2023 |
    Published 29 July 2022
    Fact Checked
    Medically reviewed by Dr. Sara Twogood, Obstetrician and gynecologist, Cedars-Sinai Medical Group, California, US
    Flo Fact-Checking Standards

    Every piece of content at Flo Health adheres to the highest editorial standards for language, style, and medical accuracy. To learn what we do to deliver the best health and lifestyle insights to you, check out our content review principles.

    Bacterial vaginosis is the most common vaginal condition, but unless you’ve had BV before, you probably won’t know a huge amount about it. We quizzed an expert on the main symptoms, what causes it, and effective treatment.

    You probably don’t spend a lot of time thinking about your vaginal discharge. However, if you notice that it starts to appear gray in color or develops a fishy smell, then it could be a sign that you have bacterial vaginosis or BV. 

    Noticing a change in the way your discharge smells may leave you feeling self-conscious or scared, but you’re far from alone. Bacterial vaginosis is the most common vaginal condition experienced by women between the ages of 15 and 44. It’s estimated that as many as one in three of us will get BV at some point in our lives — and around 84% won’t have any symptoms at all. In fact, unless you’ve had it before, you’re unlikely to know much about BV because it’s not something you usually learn about in school.

    The good news is that not only is BV common, but it’s also very treatable. Here, Dr. Amanda Kallen, Flo board member and associate professor of reproductive endocrinology and infertility, outlines exactly what bacterial vaginosis is and busts some of the common myths around the condition.

    What is bacterial vaginosis (BV)?

    Like a yeast or urinary tract infection, bacterial vaginosis is a condition that impacts your intimate health. But how does it start?

    “BV is caused by an overgrowth of normal vaginal bacteria,” Dr. Kallen explains. It may feel strange to hear about bacteria living in your vagina, but this is actually how your vagina stays “clean.” More on that below. 

    The two most common symptoms associated with bacterial vaginosis are:

    • Vaginal discharge that’s greyish-white and thin and watery
    • Discharge that has a strong fish-like odor, especially after sex

    “It can also have no symptoms,” Dr. Kallen adds. And research backs this up because BV is thought to affect almost 30% of women ages 14 to 49, although around 84% have no symptoms.

    Take a quiz

    Find out what you can do with our Health Assistant

    What causes bacterial vaginosis?

    To understand the causes of bacterial vaginosis, it’s useful to know more about the role bacteria plays in keeping your vagina healthy. 

    All vaginas have bacteria, known as vaginal flora. This is totally natural — the human body tends to have microorganisms, like bacteria, anywhere it’s exposed or connected to the outside world, such as in your mouth or gut. They help to protect your body from getting sick.  

    Bacterial vaginosis can occur when there is an imbalance of “good” and “harmful” bacteria. Usually, it’s because your levels of good bacteria drop, and other bacteria reproduce quickly. 

    “We don’t quite know the cause [for this imbalance],” Dr. Kallen explains. “But we know that some people are at higher risk.” 

    There are a few things that can upset your normal vaginal bacterial levels and increase your risk of developing BV, including: 

    • Pregnancy
    • Douching or washing the inside of your vagina with water or soap. Your vagina is a self-cleaning organ and produces fluids to help keep you clean and healthy and your vaginal pH balanced. 
    • Having sex without using a condom
    • Having an intrauterine device (also known as the IUD or contraceptive coil) placed
    • Having sex with a new person
    • Having sex with different people 
    • Having sex with someone with a vagina

    Is bacterial vaginosis a sexually transmitted infection (STI)?

    Dr. Kallen notes that there are a few big misconceptions about bacterial vaginosis, the first being “that it is caused by ‘bad’ or ‘poor’ vaginal hygiene.” We can’t stress this more: it’s not. It’s really, really not. 

    And while sex without a condom or sex with a new partner(s) may change your normal vaginal bacterial balance, bacterial vaginosis is “not a sexually transmitted infection,” she adds.

    So why has it been described as an STI in the past? Sometimes, the signs and symptoms of STIs can be similar to those of bacterial vaginosis. Unusual discharge is also linked to chlamydia, gonorrhea, and trichomoniasis (which is caused by a parasite and leads to a change in the color and smell of discharge). You can find out more about the symptoms of each by clicking on the links. 

    In fact, the signs are so similar that when you speak to your health care provider about your symptoms, they may test for STIs, bacterial vaginosis, and even a yeast infection at the same time to be sure of what they’re diagnosing you with. 

    How do you treat BV?

    The good news is that bacterial vaginosis tends to clear up on its own in around a third of cases — meaning that the balance of bacteria that normally exists in your vagina returns without treatment. However, if you notice a strong, persistent odor or you have a fever, then you should reach out to your health care provider because you might need a prescription drug. 

    Before diagnosing you, your medical professional may perform a pelvic exam and take a sample of your discharge. They will do this by swabbing the inside of your vagina with a cotton bud. 

    They’ll examine your vaginal discharge under a microscope for what’s known as “clue cells or vaginal cells with bacteria. They may also ask you to do an STI test and test your vaginal pH (how acidic your vagina is). This is because a vaginal pH of 4.5 or higher can be a sign of bacterial vaginosis. 

    The most common bacterial vaginosis treatment option is a course of antibiotics. You might be prescribed one of the following: 

    These antibiotics can be taken either in the form of pills or, sometimes, a topical gel or cream that you insert into the vagina. 

    “Occasionally, the first course of antibiotics is not effective, and further treatment is needed,” Dr. Kallen notes. So if your symptoms don’t seem to be going away, then make sure you follow up with your health care provider.

    You might wonder, if you have BV should you tell your partner? If your current partner has a penis, then it’s unlikely that they will need to be tested, too. However, if you’ve had sex with someone with a vagina, then you should consider reaching out to them and encouraging them to get tested. They might also need treatment.

    Pregnant women with BV have an increased risk of preterm delivery and other pregnancy complications.

    Bacterial vaginosis and pregnancy: What you should know?

    Bacterial vaginosis is usually nothing to worry too much about. However, if you start to experience the symptoms associated with BV during pregnancy, you should reach out to your health care provider. 

    “Pregnant women with BV have an increased risk of preterm delivery and other pregnancy complications,” Dr. Kallen explains. Before you panic, the UK’s National Health Service says that there is a small chance of complications if you develop BV while pregnant, but for many people, the condition doesn’t cause any problems. 

    If you’re at all worried or have noticed a change in your discharge during pregnancy, then reach out to your health care provider. They will be able to talk you through any changes and do any tests. 

    How to prevent bacterial vaginosis?

    Unfortunately, bacterial vaginosis tends to linger once you’ve had it. In fact, one study found that 52% of people who had been diagnosed with BV once had it again at least once more. And it’s most likely to come back in the first 3 months after it first showed up. 

    Dr. Kallen says there are a few steps you can take to try and prevent BV from coming back. “Change up your vaginal hygiene (not douching, just washing with water), wear breathable underwear (made of cotton), and avoid perfumed soaps or products.” She adds: “[BV] is not an STI, but sex with a new partner may alter your vaginal flora, so using condoms can also help.”

    Bacterial vaginosis: The takeaway

    So now we know that thin, gray discharge and a fishy odor (especially after sex) can both be symptoms of bacterial vaginosis — a common condition that is not an STI nor a sign of poor hygiene but something that happens when your vaginal bacteria balance gets thrown off. 

    If you think you might have BV, reach out to your health care provider for advice, support, and a course of antibiotics if needed.


    Aubyn, Gloria Baaba, and Daniel Nii Aryee Tagoe. “Prevalence of Vaginal Infections and Associated Lifestyles of Students in the University of Cape Coast, Ghana.” Asian Pacific Journal of Tropical Disease, vol. 3, no. 4, Aug. 2013, p. 267. Accessed 26 July 2022.

    “Bacterial Vaginosis: Diagnosis.” Mayo Clinic, 21 July 2021, www.mayoclinic.org/diseases-conditions/bacterial-vaginosis/diagnosis-treatment/drc-20352285. Accessed 26 July 2022.

    “Bacterial Vaginosis: Symptoms.” Mayo Clinic, 21 July 2021, www.mayoclinic.org/diseases-conditions/bacterial-vaginosis/symptoms-causes/syc-20352279. Accessed 26 July 2022.

    “Bacterial Vaginosis.” National Health Service, www.nhs.uk/conditions/bacterial-vaginosis/. Accessed 26 July 2022.

    “Bacterial Vaginosis.” Cleveland Clinic, my.clevelandclinic.org/health/diseases/3963-bacterial-vaginosis. Accessed 26 July 2022.

    Bacterial Vaginosis: Overview. Institute for Quality and Efficiency in Health Care (IQWiG), 2018. Accessed 26 July 2022.

    “Bacterial Vaginosis Statistics.” Center for Disease Control and Prevention, 6 May 2021, www.cdc.gov/std/bv/stats.htm. Accessed 26 July 2022.

    “Clindamycin.” Drugs.com, www.drugs.com/clindamycin.html. Accessed 26 July 2022.

    “Metronidazole.” Drugs.com, www.drugs.com/metronidazole.html. Accessed 26 July 2022.

    Jinn, Jill. “Screening for Bacterial Vaginosis during Pregnancy.” JAMA Network, 7 Apr. 2020. jamanetwork.com/journals/jama/fullarticle/2764183. Accessed 26 July 2022.

    Ravel, Jacques, et al. “Vaginal Microbiome of Reproductive-Age Women.” Proceedings of the National Academy of Sciences of the United States of America, vol. 108, Suppl. 1, Mar. 2011, pp. 4680–87. Accessed 26 July 2022.

    “Secnidazole.” Drugs.com, www.drugs.com/mtm/secnidazole.html. Accessed 26 July 2022.

    “STD Facts: Bacterial Vaginosis.” Center for Disease Control and Prevention, 2 June 2022, www.cdc.gov/std/bv/stdfact-bacterial-vaginosis.htm. Accessed 26 July 2022.

    “Tinidazole.” Drugs.com, www.drugs.com/mtm/tinidazole.html. Accessed 26 July 2022.

    Wilson, J. “Managing Recurrent Bacterial Vaginosis.” Sexually Transmitted Infections, vol. 80, no. 1, Feb. 2004, pp. 8–11. Accessed 26 July 2022.

    History of updates

    Current version (19 January 2023)

    Medically reviewed by Dr. Sara Twogood, Obstetrician and gynecologist, Cedars-Sinai Medical Group, California, US

    Published (29 July 2022)

    In this article

      Try Flo today

      Sign up for our newsletter

      Our latest articles and news straight to your inbox.

      Thanks for signing up

      We're testing right now so not collecting email addresses, but hoping to add this feature very soon.