What causes vaginal thrush?


Vaginal thrush (also called vaginal candida, yeast infection, or just simply ‘thrush’) is a fungal infection of the vulva and vagina. Thrush is common, and most women will experience at least one episode of thrush in their lifetime. Here, we discuss all things thrush – what causes it, what are the symptoms, and how it is treated.


What causes thrush?

The vagina is a complex environment with a particular range of pH (or acidity) that maintains the normal balance of organisms such as bacteria and fungus. Our own immune system also helps to keep this natural balance. Bacteria and fungus organisms are naturally occurring in the vagina, but when the balance is thrown off certain organisms may grow in higher numbers and cause symptoms. Thrush is caused by overgrowth of a type of fungus called Candida. Most thrush infections are caused by Candida albicans, however a small percentage are caused by another strain of Candida called Candida glabrata. Thrush is most common in women aged 20-40 years old, and is uncommon to occur before puberty or after menopause.


Certain medical conditions or medications can predispose a woman to thrush. These include:

  • Recent antibiotics or steroid treatment
  • Diabetes
  • Pregnancy
  • Other conditions or treatments that cause suppression of the immune system

The vaginal balance can also be affected by products applied to the vaginal and vulval area, such as soaps, moisturisers, fragrances, lubricants and spermicides. Thrush is not a sexually transmitted infection and cannot be ‘caught’ from someone else.


How do I know I have thrush?

The overgrowth of the Candida fungus irritates the vaginal lining. The symptoms commonly experienced with a thrush infection include:

  • An itchy or irritated vulva and vagina
  • A burning feeling in the vulva and vagina
  • Discharge that is thick, white and clumping together – although discharge may not always occur
  • Discomfort during sex
  • Pain during urination as the urine passes over the irritated tissues

In cases of obvious and uncomplicated thrush, testing may not be required before starting treatment. Swabs to confirm the thrush diagnosis are usually taken in cases where the diagnosis is less clear, women with recurrent thrush, or pregnant women. Your doctor may start treatment while waiting for the swab result to come back, or may wait until the swab result is back before starting treatment.


What is the treatment for thrush?

Thrush is easily treated in most cases with an anti-fungal treatment. Anti-fungal treatments are available in topical and oral preparations. The topical preparations are applied directly to the vagina and vulva, and are available in both cream and pessaries (pessaries are large tablets that are inserted into the vagina). Both of these are effective as each other and are just a different way of delivering the topical treatment, so the choice is based on a woman’s preference. Anti-fungal treatments are also available in oral tablets, which are used for women who prefer a tablet, in cases where topical preparations may not be suitable, and in thrush where the topical treatments have not worked to clear the infection.

Thrush treatments are available by prescription from a doctor. Some preparations are also available over-the-counter at the pharmacy, so women who think they may have thrush may decide to start self-treatment with an over-the-counter preparation. It is important to see a doctor if you experience more than a few thrush episodes in a year, if your thrush does not get better with over-the-counter treatment, or if you have any symptoms that are not usual for thrush.


Why do I keep getting thrush?

Some women may experience persistent or recurrent thrush. Persistent thrush is when the infection is not cleared with treatment, and recurrent thrush is when the infection clears but then occurs again at a later time. Up to 10% of women will experience recurrent thrush at some point in their lives. 

A swab test is important in women with persistent or recurrent thrush. This not only confirms the diagnosis, but can tell your doctor what strain of Candida is causing the thrush. For the 5% of thrush infections that are caused by Candida glabrata, different treatments are often required as this strain does not usually respond to the standard anti-fungal treatment.

The medical conditions and medications that predispose women to thrush can be a cause for thrush persisting or recurring, so your doctor may do other tests to check for these conditions. Medical conditions such as diabetes can be optimised to reduce the chance of thrush occurring. Some medications to treat certain conditions can predispose to thrush, so your doctor may decide to change to a medication less likely to cause thrush. Some women may require longer anti-fungal treatment duration for thrush that is persistent or recurrent, and this can sometimes be for several months.


You can help to reduce your chance of getting thrush by:

  • Avoiding using soaps, creams, moisturisers and fragrances on your vagina and vulva (unless prescribed by your doctor)
  • Avoid toilet paper, pads and tampons that are fragranced or perfumed
  • Wear cotton, breathable underwear
  • Use low allergenic or fragrance-free laundry products
  • Do not use internal vaginal washes such as douches

Could it be something else?

There are other conditions in women that can cause symptoms similar to vaginal thrush. A change to the vaginal discharge and vaginal discomfort are common symptoms for many conditions.

Depending on your symptoms and medical history, your doctor may want to check for other conditions such as:

  • Sexually transmitted infections such as Chlamydia, Gonorrhoea or Trichomonas
  • Urinary tract infection
  • Skin conditions such as intertrigo, dermatitis, psoriasis, lichen sclerosus or lichen planus
  • Bacterial vaginosis, which is an imbalance in the bacterial levels in the vagina
  • Genital herpes
  • Vulval cancer (this is uncommon)

Your doctor will be able to assess for these conditions by asking about your symptoms, taking your medical history and examining your genital area. Some of these conditions may require extra swabs or a biopsy for diagnosis. Some conditions may require a non-GP Specialist such as a Gynaecologist or Dermatologist to diagnose the condition.

You should consult with your doctor if you:

  • Have more than a few episodes of vaginal thrush in a year
  • Have used over-the-counter thrush treatment and your symptoms are persisting
  • Have symptoms or discharge that are not the usual symptoms for thrush
  • Have any rash, ulcers, sores or lumps in the vaginal area
  • Have  have any vaginal bleeding
  • Are concerned about your symptoms for any other reason

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