Causes of bacterial vaginosis

Bacterial vaginosis (BV) occurs when there's a change in the natural balance of bacteria in your vagina.

Your vagina should contain bacteria called lactobacilli, which produce lactic acid. This makes the vagina slightly acidic, which prevents other bacteria from growing there.

Women with BV tend to have a temporary shortage of lactobacilli, which means their vagina isn't as acidic as it should be. This allows other types of bacteria to grow.

It's still unclear what causes this change, although your risk is increased if you:

• are sexually active, particularly if you have a new sexual partner or multiple sexual partners
• use an intrauterine device (IUD) a contraceptive device that fits inside the womb
• smoke

For reasons that are unclear, BV is more common in black women than in other ethnic groups.

Is BV an STI?

BV isn't generally considered a sexually transmitted infection (STI) . However, there's conflicting evidence on the subject.

Evidence that suggests BVmay be an STI includes:

• rates of BV are higher in women who have multiple sexual partners
• rates of BV are lower in women who use a condom during sex

There's also evidence that women with BV can pass the condition to women they have sex with, although how this happens is still unclear.

However, there's also evidenceto suggest BV may not be an STI, as:

• there's no equivalent of BV in men
• treating male partners with antibiotics doesn't prevent the recurrence of BV
• rates of BV can vary significantly in different ethnic groups, which can't be explained by sexual activity alone
• BV can sometimes occur in women who aren't sexually active

Many experts think sexual activity plays a role in BV, but other factors are probably also responsible for the condition.

Bacteria
Bacteria are tiny, single-celled organisms that live in the body. Some can cause illness and disease, and some are good for you.

Sexually transmitted infections (STIs)
STIs are diseases passed on through intimate sexual contact, such as vaginal, oral or anal sex.

Uterus
The uterus (or womb) is a hollow, pear-shaped organ in a woman where a baby grows during pregnancy.

Vagina
The vagina is a tube of muscle that runs from the cervix (the opening of the womb) to the vulva (the external sexual organs).