What are the causes of thrush?

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Reviewed by Dr Fran Yarlett on June 1, 2023

What are the causes of thrush? | The Lowdown
If you are suffering or have suffered from vaginal thrush and aren't sure what's causing it - we've got you. Get the lowdown on why your bits won't stop itching, and what you can do about it...

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What’s The Lowdown?

  • Thrush is caused by a change in the delicately-balanced levels of bacteria and yeast in the vagina
  • These levels can be disrupted by a number of things, such as skin irritation, pregnancy, diabetes, a weakened immune system or hormones
  • Some people get vulval itching and irritation which isn’t due to thrush infection – if symptoms don’t get better with treatment or they keep coming back, seek medical advice
  • There are several ways to treat thrush, but not all treatment options are suitable for everybody

Thrush is caused by an overgrowth of a yeast called candida. It is an infection that thrives in moist, damp places (hello, vagina), and is usually harmless. You can develop thrush in your mouth, armpits, groin and even between your fingers. The vagina is an ideal location for thrush to thrive, and is one of the most common places the infection is found.

What is vaginal thrush?

To understand exactly what vaginal thrush is, we first need to understand the delicate ecosystem of the vagina itself. Our vaginas contain both bacteria and yeast, and when they’re at the right levels, they keep each other in check and maintain a perfect balance. The yeast stops the bacteria from overgrowing, and the bacteria does the same to the yeast. When something upsets this balance – and we’ll get into the culprits in a second – candida (the yeast that causes thrush) has an opportunity to thrive. 

Excess amounts of candida are what cause the symptoms of thrush, like:

  • Unusual, white, cottage cheese-like discharge
  • Burning or pain on the vulval area while urinating
  • Pain, itching, redness or swelling of your genitals
  • Discomfort or stinging to the vulval skin during sex
  • Thrush discharge does not usually have an unpleasant smell like you might find with bacterial vaginosis

Your vagina naturally has quite an acidic pH as a result of the balance of its natural ecosystem of bacteria and yeast. If this pH is altered, it can make it easier for candida or thrush to overgrow. 

What are the causes of vaginal thrush?

There are many things that can tip the metaphorical bacteria-yeast scale in your vagina and cause a bout of thrush. Before we get into the most common causes, it’s important to note that thrush isn’t classed as an STI, but can be shared between sexual partners and it can be triggered by sex. This is because, during vaginal sex, the equilibrium we talked about before can be thrown off balance by pH changes due to semen, lubricants and condoms

Damaged or irritated skin

If the skin around your vagina is irritated or damaged, you are more likely to develop thrush. This is because thrush grows more easily on damaged skin, where it can live under the surface. Be sure not to use soaps or perfumes on vulval skin, as these can cause further damage.  Intimate washes may sell themselves as being good for vaginal health but actually can cause more harm than good.

We have a great team of doctors here at The Lowdown who can give you tailored advice about thrush in a one-to-one consultation.


Candida is a yeast fungus, not a bacterial infection, so antibiotics won’t work to get rid of it. In fact, quite the opposite: you are more likely to develop thrush if you are taking antibiotics. Antibiotics work by killing off the good bacteria. Can you guess what’s coming next? Your vagina relies on certain good bacteria to keep its amount of yeast fungus in check – it all circles back to that delicate equilibrium between bacteria and yeast. The death of these good bacteria can allow space for candida to grow out of control.


If you have diabetes, you might find that you develop vaginal thrush more easily. This is because candida thrives on sugar, and there is more sugar in your blood if you are diabetic than if you are not. The sugar in your blood also makes its way into your urine, sweat and saliva, making your body more prone to a thrush infection. The better controlled your diabetes, the less likely you are to get thrush infections.

Weakened Immune System

There are many reasons why someone might have a weakened immune system. Genetic disorders, certain medications and cancer treatment can all reduce the efficacy of the immune system, making it harder to fight off infections and making thrush more likely to take hold.

If you have a weakened immune system, your immune cells won’t fight off thrush as effectively as they might otherwise. This can cause thrush to spread to other areas of your body, and can be quite dangerous. If you know you have a weakened immune system and the thrush treatments you have tried aren’t working, make sure to see your doctor. 

Hormone Replacement Therapy (HRT)

Studies have shown that postmenopausal women on hormone replacement therapy (HRT) are more likely to develop thrush than those who are not on hormone replacement therapy. This is because oestrogen (a key component of HRT) causes cells to produce glycogen (a stored sugar), which can, in turn, cause candida to overgrow.

The menstrual cycle and contraception

The natural hormonal changes you experience during your cycle can lead to imbalances in the vagina. That’s why you’re more likely to develop thrush around your period. Specifically, it’s high levels of oestrogen which seem to increase the risk of thrush.

The hormones found in contraception are artificial versions of the hormones found in your own body, but synthetic oestrogen can still cause the balance of bacteria and yeast in your vagina to become, well, unbalanced and itchy. Check out our blog about how contraception might lead to vulval itching.

Check out the contraception reviews | The Lowdown

Can the coil cause thrush?

There is conflicting research about whether coils can cause thrush. Some studies show that there is an association between coils and thrush, others have found no link whatsoever. There is a theory that thrush yeasts can stick to coils inside the womb making it harder for treatments to fully work, and therefore increasing the risk of recurrent thrush. While the evidence isn’t compelling, guidelines do suggest that recurrent, symptomatic thrush that isn’t responding to treatment in those who have a coil, could benefit from a switch of contraception. If this affects you, why not use our contraception recommender to find a better option?


In the same hormonal vein, pregnancy also increases your likelihood of developing thrush. When you’re pregnant, the levels of oestrogen and progesterone in your body change, which can cause the levels of bacteria and yeast in your vagina to change, too. The levels of oestrogen in your body in particular can have an impact, as it can make your cells more susceptible to the growth of glycogen (a stored sugar), which can increase candida growth. 

If you are pregnant, you should speak to your healthcare provider before you use thrush treatment, as some will not be suitable for you.

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When to see a doctor about thrush

You should seek medical advice if:

  • Your thrush doesn’t go away with the appropriate treatment, or if it keeps coming back.
  • If you are pregnant, or have a weakened immune system, and suspect you have thrush.
  • If your thrush appears to be spreading, or getting worse despite treatment. 

Thrush doesn’t usually lead to ulcers, smelly discharge, bleeding, pelvic pain or deep pain during sex. If you have these symptoms then contact your local sexual health clinic ASAP.

How to treat the symptoms of thrush

The good news is that thrush is pretty common, rarely serious and generally easy to treat. You can treat thrush using an oral tablet, a pessary (a tablet you put inside your vagina) or a cream. like Canesten on Amazon (affiliate link btw!)

Most people can use oral antifungal medication alongside a cream or pessary, which may help to relieve the irritating symptoms of thrush, like itching and discomfort. If you are pregnant, you should not take oral Fluconazole capsules, and should speak to a doctor or healthcare provider before beginning thrush treatment, usually with vaginal pessaries.

If you have a regular sexual partner, it is worth checking whether they have noticed any itching or redness to their bits. They should be treated too if they have any symptoms.

If you’re still not sure which treatment might help you, book a consultation with one of our lovely doctors. They’ll be able to talk you through your options and help you find a solution that’s right for you.

Contraception recommender | The Lowdown

  1. Dennerstein, G. J., & Ellis, D. H. (2001). Oestrogen, glycogen and vaginal candidiasis. Australian and New Zealand Journal of Obstetrics and Gynaecology, 41(3), 326-328.
  2. 2022. Diabetes and Thrush. [online]. [Accessed 5 June 2022]
  3. Fischer, G. and Bradford, J., 2011. Vulvovaginal Candidiasis in Postmenopausal Women. Journal of Lower Genital Tract Disease, 15(4), pp.263-267.
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  7. NHS. 2022. Fluconazole: medicine to treat fungal infections including nail infections. [online]. [Accessed 31 May 2022].
  8. NHS. 2022. Thrush. [online]. [Accessed 1 June 2022]
  9. NHS. 2022. Thrush in men and women. [online] [Accessed 1 June 2022]
  10. NCBI. 2022. How can you prevent oral thrush?. [online] [Accessed 1 June 2022]
  11. Royal College of General Practitioners. 2013. Sexually transmitted infections in primary care. [online] [Accessed 5 June 2022]
  12. WebMD. 2022. Diabetes and Thrush. [online] [Accessed 1 June 2022]
  13. Patient. 2021. Vaginal Thrush. [online]
  14.  Faculty of Sexual and Reproductive Health. FSRH Guideline Intrauterine Contraception. March 2023

Mary Hargreaves is a writer and author with a passion for women’s reproductive health. She has a Masters in Clinical and Health Psychology, and has worked in scientific research across a range of disciplines.