What Is The Main Cause Of BV?

There isn't one single cause of bacterial vaginosis. It's an imbalance, not an infection you catch from one specific place, which is exactly why it can feel so hard to pin down. Here's what's actually happening in your body, and the full list of everyday things that can tip that balance the wrong way.

What's actually going on

A healthy vagina is dominated by Lactobacillus bacteria, which produce lactic acid and keep things acidic enough (a pH below 4.5) to stop harmful bacteria taking hold. BV happens when lactobacilli numbers drop and anaerobic bacteria, most notably Gardnerella vaginalis, overgrow and push the pH higher. Everything below is a way of triggering that shift, not a separate cause in its own right.

Sex and semen

Sexual activity is one of the most consistently cited risk factors, and semen itself is part of the reason why: it's alkaline, so unprotected sex can temporarily raise vaginal pH and disturb the bacterial balance. Having a new partner, multiple partners, or not using condoms all increase the odds. This is also the area of BV research that's moved fastest recently, including new evidence that a partner's own bacteria may play a more active role than previously thought. We've covered that research, including whether BV should be considered contagious, in Can BV mean STD? and in Who Is Most Likely To Get BV?

Douching and vaginal washing

Douching is one of the clearest, most repeatedly confirmed triggers in the research, cited by the NHS, CDC and WHO alike. Washing inside the vagina strips out protective lactobacilli along with everything else, leaving room for harmful bacteria to move in. The vagina is self-cleaning, so internal washing of any kind, whether that's water, soap or a dedicated douching product, tends to do more harm than good.

Perfumed products and intimate hygiene habits

Scented soaps, bubble bath, intimate sprays, deodorants and scented wipes are all commonly flagged triggers. These products can irritate the vaginal lining and disrupt its natural pH, and NHS guidance specifically advises against using any of them in or around the vagina, sticking instead to water and a plain, unperfumed soap on the outside only.

Clothing and moisture

Tight, non-breathable underwear, particularly synthetic fabrics like nylon, can trap moisture and heat against the skin, creating conditions that favour bacterial overgrowth. The same goes for sitting in damp gym kit or a wet swimsuit for long periods. Cotton underwear and getting out of sweaty clothing promptly are both simple, low-effort ways to reduce this particular risk.

IUDs and hormonal changes

Both the NHS and CDC list IUDs (coils) as a recognised risk factor for BV, though it isn't fully understood why. Hormonal shifts more broadly, including those around your period or from hormonal contraception, can also affect the vaginal environment enough to make BV more likely for some women.

Diet

The evidence here is thinner than for the factors above, but a high-fat, low-fibre or sugar-heavy diet has been associated with a less favourable vaginal pH in some research, which may make bacterial overgrowth more likely. It's a smaller piece of the puzzle rather than a primary cause on its own.

Smoking

Smoking is independently linked to both a higher risk of developing BV and a higher risk of it recurring. The exact mechanism isn't settled, but it's one of the more consistent lifestyle associations in the research, alongside stress.

Stress

Chronic stress raises cortisol, and cortisol can affect vaginal pH regulation, so there's a plausible pathway from ongoing stress to a higher chance of BV. It's not the biggest lever most women can pull, but it's worth knowing about if you're already addressing the more common triggers and still getting BV.

Can you get BV without any of the above?

Yes. Some women have naturally lower levels of protective lactobacilli, which may be partly genetic, and this alone can make BV more likely regardless of hygiene, diet or sexual activity. This is also why women who have never had sex can still develop BV. If none of the triggers above sound familiar and you're still getting recurrent episodes, that's a conversation for a GP or sexual health clinic rather than something to keep troubleshooting alone.

For what BV can lead to if it isn't treated, see What does untreated BV lead to? And if you're looking at ways to support your vaginal flora and reduce the chances of BV returning, we've covered the evidence on probiotics in Can I Get Rid Of BV By Taking Probiotics?