When the balance tips: bacterial vaginosis and thrush explained

An unusual smell, an unfamiliar discharge, or sudden itching can be unsettling, and it’s natural to wonder what’s going on. Two of the most common explanations are bacterial vaginosis (BV) and vulvovaginal candidiasis (VVC), more commonly known as thrush. They can look similar on the surface, but they have very different causes.

So, what exactly are BV and thrush, and how can you tell them apart?

Bacterial vaginosis: when the ecosystem shifts

Bacterial vaginosis is a common condition in which the normal balance of bacteria in the vagina becomes disrupted.

Lactobacillus usually helps maintain an acidic vaginal environment. With BV, there is often a reduction in these protective bacteria alongside an overgrowth of other bacterial species, causing the vaginal environment to become less acidic.

This shift can produce:

• Thin, watery, white or grey discharge
• A strong, fishy smell, often more noticeable after sex

Interestingly, around half of people with BV have no symptoms at all - another reminder that what’s happening in the microbiome isn’t always something you can feel or see. ^[1]

What causes BV?

There isn’t one single cause. BV has been associated with a range of factors, including:

• Sexual activity or a new sexual partner
• Douching
• Products that disrupt the vaginal environment

Important to know: BV is not classed as a sexually transmitted infection (STI). ^[2]

Vaginal thrush: when yeast overgrows

Unlike BV, thrush is caused by a fungus, usually a type of yeast called Candida albicans.

Candida can actually live harmlessly in the vagina without causing any problems. It’s what’s known as an opportunistic pathogen: given the right opportunity, such as a change to the normal vaginal environment, it can overgrow and start to cause symptoms. ^[3]

What should you look out for?

The most common signs of thrush include:

• Intense itching or irritation
• Soreness and redness
• A thick, white discharge, often compared to cottage cheese
• Stinging when urinating, or discomfort during sex

Unlike BV, thrush discharge doesn’t usually come with a strong or fishy smell - one of the clearer ways the two conditions differ. ^[4]

What causes thrush?

Several everyday factors can increase the risk, including:

• Antibiotic use
• Pregnancy
• Hormonal changes
• Diabetes
• Irritation

Important to know: thrush is also not classed as an STI, and it’s usually straightforward to treat with antifungal medication. ^[3]

When to seek support

Because BV and thrush can share overlapping symptoms - and other conditions can present similarly - it’s best not to self-diagnose based on symptoms alone. A GP, pharmacist or sexual health clinic can assess what’s going on, rule out other causes, and offer the right treatment.

The bigger picture

BV and thrush are two different examples of the same underlying idea: the vagina is a living ecosystem, and its balance can shift for all kinds of ordinary reasons.

Neither condition is something to feel embarrassed about, and neither is something you should simply put up with. An unusual smell, discharge or discomfort is your body’s way of flagging that something has changed, and understanding why is the first step toward feeling like yourself again.