What is candida, and how does it cause thrush?

The human body is naturally full of millions of bacteria and fungi (yeasts). This is completely normal and these organisms form part of the human body, its functions, and its interactions with the world around it.

On the skin, these colonies of bacteria and fungi are known as skin flora. Among the bacteria, our skin is also colonised by yeasts, including candida. Other parts of our bodies, such as our gut, are colonised with bacteria and fungi too. These include bacteroids, lactobacillus, and actinobacteria, and are thought to play an important role in maintaining a healthy gut.¹

Thrush or candidiasis occurs when someone has an overgrowth of the fungi that naturally occurs on the skin. Technically, thrush is a fungal infection caused by any type of candida (there are actually over 20 types). In practice, however, it is most likely to be caused by a strain called Candida albicans.² Thrush can occur in a number of locations, including in the mouth and on the skin. This article looks at vaginal thrush, also known as vulvovaginal candidiasis.

Vulvovaginal candidiasis (genital thrush) occurs when there is an overgrowth of candida, causing the genital area to become inflamed and uncomfortable. Up to 9 in 10 cases of genital thrush are caused by Candida albicans.³ Other types of yeast are implicated in some cases however, for example Candida glabrata.

What causes thrush?

Certain things can trigger genital thrush, for example, a change in vaginal pH (how acidic or alkali the vagina is). Where you’re at during the menstrual cycle can also affect the balance, and most people who menstruate are more likely to develop thrush around the time of ovulation. The reason for this is thought to be due to an increased level of the hormone oestrogen at this time.⁴

These increased oestrogen levels have been linked with decreased immune system activity around ovulation, which is thought to help the survival of sperm when it enters the reproductive tract.⁵ More studies are being done on this, but it is thought that decreased activity in the immune system results in an increased susceptibility to a number of illnesses, including thrush.

Most cisgender women will have thrush at some point in their life and may be aware of the principal symptoms

Antibiotics can also affect the balance of vaginal pH. While they are taken to treat infection, they can also remove bacteria that normally lives on the surface of your skin. These bacteria are important for helping control candida overgrowth and maintaining a balance of the skin flora. If these bacteria are destroyed, it can result in candida overgrowth, and thrush develops.⁶

Thrush often occurs in fit and healthy people without an obvious cause. However, certain conditions do make you more susceptible to it. These include uncontrolled diabetes, and those with cancer or HIV. With diabetes, increased blood sugar levels can result in years of candida overgrowth, as during this time sugar acts as an energy source. This can result in thrush.

In addition, people who are on the combined oral contraceptive pill, hormone replacement therapy, or who are pregnant are at increased risk.⁷ As with the menstrual cycle, it is thought that increased levels of oestrogen hormones in these three circumstances makes you more susceptible.

Most cisgender women will have thrush at some point in their life and may be aware of the principal symptoms.⁸ Typically, the area may feel itchy or sore with some stinging when passing urine. The skin may be red and inflamed. There may also be a “curdy” change or increase in vaginal discharge as well.

Indications that your symptoms may not be thrush

If your discharge is an unusual colour (for example, a green or brown shade), or has an offensive smell, then this is not thrush, especially if you have had unprotected intercourse. Symptoms such as bleeding after intercourse or in between your periods should never be put down to thrush either, as they may be a sign of a different infection or something more serious. Be sure to get checked.

There are other genital infections to be aware of, including bacterial vaginosis and trichomoniasis, both of which present with the production of offensive smelling vaginal discharge, among other symptoms. Increased discharge could also be the result of a foreign body. It can be very common to forget to remove that last tampon at the end of your cycle, so be sure to double-check.

Treatments for thrush

Treatments come in a variety of forms, but all work similarly by containing an anti-fungal medication (for example clotrimazole) to reduce the candida imbalance. These treatments can be in the form of a capsule (e.g. fluconazole), vaginal pessaries (e.g. clotrimazole pessaries), or internal creams. There are also external creams that can be used for symptomatic relief. Reducing the amount of candida you have helps to restore the normal balance of flora in your vagina.

General advice to help you avoid thrush

About 75% of cisgender women suffer from vulvovaginal thrush at some point in their life.⁹ The majority only have it once or twice, but it is more troublesome for others who have it more often.

See your doctor if this is your first case of thrush, if you are not sure your symptoms are thrush, if you suffer recurrent thrush, or if you are pregnant

There are various self-care tips that may help. These include washing the vulval area (on the outside only) with water or a soap substitute (a gentle, non-scented moisturiser) and to consider the use of using probiotics orally. There is little solid evidence to suggest whether oral probiotics help prevent thrush, and while there is also little evidence of harm, avoiding these is recommended.¹⁰

Expert opinion states that the avoidance of soap or shower gels or feminine hygiene products in the vulval area and the avoidance of tight, non-cotton based clothing is also helpful.¹¹ In addition, vaginal douching should be avoided.

See your doctor if this is your first case of thrush, if you are not sure your symptoms are thrush (especially if you have other symptoms as well), if you suffer recurrent thrush (more than two cases in six months), or if you are pregnant. Many thrush treatments are not safe in pregnancy, so please do not self-treat without taking advice. Thrush is a common complaint, but most people are able to manage it easily and effectively with the above advice. Remember, if in doubt, check with your doctor.

Featured image is of a scientist holding a petri dish that contains a specimen sample. There is a row of samples in small bottles on the table in front of them, which are in the background of the shot

Last updated April 2022
Next update due 2025