Vaginal thrush is a yeast infection that is usually caused by a type of fungus that lives naturally in the vagina.
Over 90% of cases of thrush are caused by Candida albicans. The rest are due to other types of Candida fungi.
Up to half of women have Candida living naturally in their vagina without it causing any symptoms.
It's believed that a change in the natural balance of the vagina leads to the growth of Candida and causes the symptoms of thrush.
This can be a chemical change – for example, when you take antibiotics – or it can be a hormonal change – such as during pregnancy.
What increases your chances of thrush?
Your risk of developing thrush increases if you:
- take antibiotics
- are pregnant
- have poorly controlled diabetes
- have a weakened immune system
Thrush happens in about a third of women who take antibiotics, because antibiotics get rid of the friendly bacteria in the vagina.
Any type of antibiotic can increase your chances of developing thrush, but for you to develop the yeast infection, the Candida fungus must already be present in your vagina.
If you're pregnant, changes in the levels of female hormones, such as oestrogen, increase your chances of developing thrush and make it more likely to keep coming back.
Diabetes is a long-term condition that's caused by too much glucose in the blood. It's usually kept under control by having regular insulin injections and maintaining a healthy, balanced diet.
If you have poorly controlled diabetes – when your blood glucose levels go up and down, rather than being stable – you are more likely to develop thrush.
Weakened immune system
Your risk of developing thrush is also increased if your immune system is weakened – for example, when you have an immunosuppressive condition, such as HIV or AIDS, or if you are having chemotherapy.
This is because in these circumstances your immune system, which usually fights off infection, is unable to control the spread of the Candida fungus.
Read about how thrush is diagnosed.