Thrush, vaginal

Vaginal thrush is caused by fungus that occurs naturally in the vagina. A type of fungus called Candida albicans is the most common cause of vaginal thrush, although a number of other types of Candida fungi are sometimes responsible.

Candida fungi

The main types of Candida fungi that cause thrush are:

• Candida albicans - which is responsible for 80-92% of cases, and
• Candida glabrata - which is responsible for about 5% of cases.

The remaining cases of thrush may be caused by:

• Candida tropicalis,
• Candida parapsilosis,
• Candida krusei,
• Candida kefyr,
• Candida guilliermondii, or
• Saccharomyces cerevisiae.

The Candida type of fungus is found in 20-50% of women who do not have any symptoms of thrush. It is therefore thought that there must also be other changes that take place in the vagina that cause the symptoms of thrush.

A number of factors are known to trigger thrush, while others are suspected of triggering it. The accepted and possible risk factors for thrush are described below.

Accepted risk factors

The following factors are known to increase your risk of developing thrush.
 
Antibiotics

Thrush occurs in about 30% of women who are taking a course of systemic, or intravaginal, antibiotics (medicines used to treat infections caused by bacteria; they can either be taken orally (by mouth) or inserted into the vagina).

Any type of antibiotics can increase your risk of developing thrush, but in order for you to develop the condition, the Candida fungus must already be present.

Pregnancy

If you are pregnant, changes in the levels of female sex hormones, such as oestrogen, make you more likely to develop thrush. During pregnancy, the Candida fungus is more prevalent (common), and recurrent infection is also more likely.

Diabetes (poorly controlled)

Diabetes is a chronic (long-term) condition that is caused by too much glucose in the blood. The condition is usually controlled through insulin injections or through your det. If you have diabetes that is poorly controlled, you are more likely to develop thrush.

Immunodeficiency

Your risk of developing thrush is also increased if your immune system is weakened - for example, by an immunosuppressive condition, such as HIV or AIDS, or if you are receiving chemotherapy (a treatment for cancer). This is because in these circumstances your immune system, which usually fights off infection, is unable to effectively control the spread of the Candida fungus.

Possible risk factors

The following factors may trigger thrush, but at the moment there is not yet enough evidence to be certain.

Contraceptives

It is thought that contraceptives, particularly combined oral contraceptives, increase the risk of thrush. However, the results of studies carried out in this area have been inconclusive.

Sexual behaviour

Thrush is more common during the years of sexual activity, although there is only weak evidence to suggest that sexual behaviour is linked to thrush.

Activities that may cause minor abrasions (scratches) to the surface of the vagina, such as sexual intercourse, may increase your risk of developing thrush. There is also some evidence to suggest that women who have oral sex may be at greater risk of developing thrush.

There is no benefit from treating the male partner of a woman with thrush, if he does not have any symptoms. However, if your partner develops the symptoms of thrush, he should also be treated.  

Tight-fitting clothing

Wearing tight-fitting clothing, such as tights, or using panty-liners, may increase your risk of developing thrush. However, the evidence to support this is still uncertain.

Female hygiene

There is little evidence to suggest that sanitary towels are a risk factor for thrush. There is also no evidence that tampons, or vaginal douching, are risk factors for developing the condition.