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Women's health centre

Bacterial vaginosis - Causes of bacterial vaginosis

NHS Choices Medical Reference

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

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

However, if you have BV, you have less lactobacilli, which means your vagina is not as acidic as it should be. This allows other types of bacteria to grow.

It is still unclear what causes the change in the balance of bacteria, although the risk is increased if you:

  • are pregnant
  • have a new sexual partner
  • have multiple sexual partners
  • use an intrauterine device (IUD), a contraceptive device that fits inside the womb
  • smoke
  • use scented soaps or bubble bath
  • put antiseptic liquids in the bath
  • wash or clean out your vagina with water or other fluids
  • use vaginal deodorant
  • use strong detergents to wash your underwear
  • have previously been infected with the human papilloma virus (HPV) - a group of viruses that can cause genital warts and, less commonly, cervical cancer
  • eat a diet high in carbohydrates, such as lots of white bread, baked potatoes and processed food

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

Is bacterial vaginosis an STI?

It is unclear whether BV is a sexually transmitted infection (STI) as there is conflicting evidence on this issue.

Evidence that suggests BV could 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 is also evidence that women with BV can pass the condition to women they have sex with, although exactly how this happens is still unclear.

Evidence that suggests BV may not be an STI includes:

  • treating male partners with antibiotics does not prevent the reoccurrence of BV
  • rates of BV can vary significantly in different ethnic groups, which cannot be explained by sexual activity alone
  • BV can occur in women who are not sexually active

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

It may also be possible that an initial episode of BV is caused by some type of sexual infection, but further episodes are caused by other factors.


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.


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


The vagina is a tube of muscle that runs from the cervix (the opening of the womb) to the vulva (the external sexual organs).
Medical Review: January 03, 2012
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