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What Causes Bacterial Vaginosis?

Bacterial Vaginosis is caused when the vagina's natural bacterial levels are disturbed, leading to symptoms such as a strong, fishy smell and abnormal discharge. According to the female hygiene brand Canesten, Bacterial Vaginosis, otherwise known as BV, is the most common cause of vaginal infections in women of childbearing age.

The vagina contains thousands of bacteria, otherwise known as lactobacilli, which keep the natural pH balance at a slightly acidic 4.5. BV is triggered when lactobacilli levels drop and the vagina loses its natural acidic pH balance, becoming more alkaline. This change in bacterial and pH level allows for the growth of abnormal bacteria.

BV is unique to the vagina - there is no equivalent place on a man where lactobacilli and anaerobic bacteria are attempting to live in balance. For this reason, and the fact that BV can be contracted without engaging in sexual intercourse, BV is not considered an STI. Overall, as many as 1 in 3 women can expect to experience Bacterial Vaginosis in their lifetime.

What are the Main Causes of BV?

1. Douching, Over cleaning or Using Scented 'Feminine Hygiene' Products

One of the most amazing and often overlooked abilities of the vagina is that it is almost entirely self-cleaning. The vagina releases regular secretions (discharge) which expel fluids and old cells from the uterus, cervix and vagina. This discharge keeps the vagina clean, moist, and protects it from infection. By simply maintaining a healthy lifestyle (exercising, washing regularly and eating a balanced diet) the vagina will take care of itself, without the need of 'feminine care' products.

Douching (flushing water up into the vagina) and washing with scented wipes, treatments etc. will only act to disturb the vagina's lactobacilli, disrupting the pH balance and leading to the increased occurrence of BV. This risk is even greater during menstruation when the vagina's bacterial balance is significantly disrupted, according to a study published by the National Institute of Health.

In a noteworthy article for The Guardian, Rose George explains how the 'feminine care' industry capitalises on a fear of 'smelling', brought on by the fact that the vagina is still a controversial topic of conversation (even more so than actual sex) and so education on it remains limited. As she states, 'To ensure cleanliness, the vulva needs nothing fancier than water, mild soap and a gentle pat dry (do not rub)'.

As the NHS website makes clear, it is completely normal for the vagina to have a scent, thus the overuse of scented and unnatural feminine care products is not only unnecessary, but one of the key triggers to the onset of BV.

2. Sexual Activity

Although not all the links are completely clear when it comes to how sexual activity affects the onset of BV, there is strong evidence to suggest that having multiple sexual partners and same-sex female relationships increases the risk of developing BV.

Having multiple male partners may increase the risk of BV as while not able to 'contract' it themselves, the penis is able to carry microbiota associated with BV and pass it between females. Uncircumcised male partners may act as a 'reservoir', increasing the likelihood of acquiring an infection after sexual intercourse. Heterosexual sex can also affect the vagina's natural pH balance as semen has a pH of 7.0 to 8.0, leading to temporary alterations in the vagina's bacterial flora. For this reason, symptoms for BV are also most noticeable after sex, where the discharge will smell particularly strong and be thicker in appearance.

Engaging in female-female intercourse can increase the risk of BV by up to 60%, and it is common for partners in these instances to re-infect each other. It is advised for both partners to be treated (even if only one displays symptoms) to reduce the risk of redevelopment.

Measures to prevent the spread of BV include reducing the number of sexual partners you might have and using condoms in heterosexual relationships. Using a condom while the female is undergoing BV treatment is also advisable as this will help prevent reinfection. It is also recommended that individuals familiarise themselves with the symptoms of BV so that it can be identified and treated as soon as possible.

3. Smoking

There is substantial evidence to demonstrate that smoking increases the chances of contracting Bacterial Vaginosis. This is because both the presence of Benzopyrene Diol-Epoxide (BPDE) and the anti-estrogenic effect of smoking itself reduces the number of lactobacilli in the vagina – allowing for the introduction of harmful bacteria.

The key research establishing this link is Brotmen et al's study into the Association between cigarette smoking and the vaginal microbiota. Other factors established through this study which could also affect the prevalence of BV are the increase in bacterial infection, physiological and structural changes, the increase in bacterial virulence and the dysregulation of the immune system – all side effects of smoking tobacco.

4. Having a Copper IUD

According to the NHS and the CDC, women who chose the Copper Intrauterine Device or IUD as a form of sexual protection were more likely to experience Bacterial Vaginosis than those who did not. This could be due to factors such as the copper affecting the PH balance of the vagina – but is most likely due to the onset of heavier, prolonged periods.

Prolonged or heavy periods can increase the risk of developing BV as menstruation is the time when the vagina's lactobacilli are most off-kilter, thus small PH changes (due to douching, sex etc.) can have a greater negative effect. For those women who develop heavier and longer periods due to the copper IUD and experience recurrences of BV, the removal of the IUD contraceptive is often recommended.

5. Taking Antibiotics

Completing a course of antibiotics can kill off 'good' bacteria in the body alongside the bad, and thus can contribute to a bacterial imbalance. This is a key reason as to why you are more likely to contract BV after antibiotic treatment for STI's (such as chlamydia). Unfortunately, this issue is twofold, as you are also more likely to re-contract potential STI's after treatment for BV (due to the antibiotics and the loss of 'good' bacteria).

Read more: Why should you always finish your antibiotics?

Other notable factors

Other factors known to contribute to the occurrence of BV can include:

The use of sex toys
In this instance it is key to ensure that the toys are kept properly clean using pH-neutral cleaning products before insertion into the vagina.
Tight-fitting underwear
Wearing tight, non-breathable underwear for long periods of time can prevent the vagina from receiving the ventilation it needs an incidence of BV. Fabrics such as nylon, polyester, lace or other synthetic materials are best avoided, along with underwear styles such as thongs or G-strings. Breathable, natural fabric such as organic cotton is recommended for long journeys or during your period, alongside loose-fitting styles like girl-boxers or traditional briefs.

When to see a doctor?

Approximately 50% of women with Bacterial Vaginosis are asymptomatic (show no symptoms), however when present, bacterial vaginosis is characterized by a fishy-smelling, thin, grey/white homogeneous discharge that is not associated with itching or soreness. There may also be a burning sensation while urinating and occasionally itching – although these symptoms are more widely associated with thrush.

What is the Standard Treatment for BV?

Mild BV symptoms may disappear on their own, however your GP will usually prescribe antibiotics for the treatment of Bacterial Vaginosis. A standard prescription will be 400mg oral Metronidazole twice a day for 5 to 7 days. There are also options to treat the infection with an intra-vaginal gel or with Clindamycin.

Recurrence of Bacterial Vaginosis

Reported cure rates for an episode of BV are estimated to be between 70% and 80%. Unfortunately, more than 50% of BV cases will recur at least once within the following 12 months. This is largely because infection-fighting bacteria have been diminished through the occurrence of BV itself and the prescription of antibiotics.

While probiotics containing lactobacilli are available for over the counter purchase, there is limited evidence to suggest that consuming these can reduce the risk of recurrent BV.

However, using condoms can reduce the likelihood of recurrence as this prevents semen from further disrupting lactobacilli levels and prevents potentially harmful bacteria from being reintroduced to the vagina.



Authored & Reviewed By

Mohamed Imran Lakhi

MPharm - Lead Pharmacist
Imran Lakhi is the superintendent pharmacist and founder at Prescription Doctor. He has been at the core of our team.

Published on: 23/09/2019 Reviewed on: 18/02/2021
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