Reviewed May 2018
What your menstrual cycle has to do with recurring thrush
Being such a common condition, it is likely that many women are familiar with vaginal thrush (Candidiasis). It is a fungal infection caused by an overgrowth of Candida (a form of yeast) in the vaginal mucosa, and it is said that 75% of women will have at least one episode of thrush within their lifetime.1
Symptoms are nonspecific, and include vaginal itching, and a thick, curd-like vaginal discharge. Some women also experience pain or discomfort during urination and sexual intercourse.
Candida is a part of the normal vaginal flora. Its growth is kept under control by the other bacterial microbes of the normal flora (predominantly Lactobacillus) which coexist causing no harm to the human host. However, certain changes in the vaginal environment, or host immunity, may disrupt the balance of this normal flora, leading to overgrowth of Candida and thus giving rise to symptoms of thrush.
When is it considered recurrent thrush?
Evidence suggests that five out of 100 women who develop thrush in the reproductive age will get a recurrence.2 The diagnosis of recurrent thrush is made when a woman gets four or more symptomatic episodes per year. She must be symptom free or have periods of partial symptom resolution in between episodes, and at least two of the episodes need to be proven by microscopy or culture.
Menstrual cycle and thrush: the role of hormones
If you are suffering from recurrent thrush you may have noticed that it worsens during a specific time in the month. Many women say that the condition often flares up right before, or in the week preceding, menstruation.
Several studies have looked into this, and found that symptoms of thrush tend to appear in the latter part of the menstrual cycle, or, more specifically, on days 19-24 of the cycle, just before menstruation.3
Increased oestrogen levels in the blood are associated with increased growth of Candida in the vagina, and the growth of Candida appears to be stimulated by oestrogen.
As you may have already guessed, fluctuating hormone levels do play a role, with oestrogen playing the key role. Research shows that hyperoestrogenemia (increased oestrogen levels in the blood) is associated with increased growth of Candida in the vagina,4 and that growth of Candida appears to be stimulated by oestrogen.5
The menstrual cycle consists basically of two phases, the follicular phase and the luteal phase. The follicular phase begins when you begin menstruating, and continues up until ovulation, after which the luteal phase begins.
Oestrogen levels are low at the beginning of the cycle, begin to rise in the mid follicular phase, and peak just before ovulation. Levels then drop following ovulation, but rise again in luteal phase and maintain a sustained increase until the levels drop at the end of the cycle.
It is believed that this increased oestrogen in the middle of the cycle promotes Candida growth, leading to symptoms appearance towards the end of the cycle.
How does oestrogen promote Candida growth?
Oestrogen exerts many complex effects both on the vaginal epithelial cells (inner lining of the vaginal wall) and Candida yeasts. Multiple effects of Oestrogen on the vaginal cells ultimately makes the human host more vulnerable to infections.6 Oestrogen promotes production of glycogen within the vaginal cells, and increased glycogen acts as an ideal source of food for growing Candida. Oestrogen also acts on Candida yeasts and promotes its growth, and improves its ability to cling onto vaginal epithelial cells.7
These changes together favour the overgrowth of Candida, and further studies are being conducted to gain a better understanding of these mechanisms.
This explains why pregnant women, and those who are on the combined oral contraceptive pill (COCP) or hormone replacement therapy (HRT) are more at risk of developing thrush, as all these situations are associated with high oestrogen levels. It also explains why thrush is less common in prepubescent girls and postmenopausal women who have relatively low oestrogen levels.
Vaginal pH and thrush
Some women say that their thrush is the worst when they have their period, or shortly after. This is believed to be related to the change of the pH value within the vaginal cells during menstruation. The pH level is a measure of how acidic or alkaline a substance is with 7 being neutral, less being acidic and more being alkaline.
During menstruation, the presence of blood in the vagina raises the vaginal pH above normal, disrupting the usual environment and favouring the growth of Candida. This can be worsened by the use of tampons which further trap menstrual blood within the vagina for longer.
The normal vaginal pH is maintained in the acidic range around 3.5 – 4.5. Evidence suggests that this low vaginal pH inhibits the growth of Candida, and therefore increases in pH are likely to promote its growth.8
Human blood is comparatively more alkaline, with a pH of around 7.35 – 7.45. During menstruation, the presence of blood in the vagina raises the vaginal pH above normal, disrupting the usual environment, and favouring the growth of Candida. This can be worsened by the use of tampons which further trap menstrual blood within the vagina for longer. This also explains why women are at increased risk of thrush in other instances where the vaginal pH is altered, such as vaginal douching and if you use various vaginal cleansers.
What can help if your recurring thrush is related to your menstrual cycle?
Even if you think that your thrush is related to the menstrual cycle, you are not completely at the mercy of your hormonal changes. Proper treatment is available and there are alternative ways to help relieve symptoms.
If you do a web search on advice and home remedies for recurrent thrush you will get a whole list of options ranging from dietary changes to inserting various herbs and suppositories into your vagina.
However, not all these are scientifically proven and therefore it cannot be guaranteed that the benefits outweigh the risks at all times. For example, there is no evidence to support the use of oral or vaginal probiotics or Lactobacillus, and using tea tree oil may cause allergic reactions in some people. Avoid vaginal douching and use of other vaginal deodorants and sprays which may alter the vaginal pH. Avoid the use of tampons, especially if your thrush outbreaks occur at the same time as menstruation.
It might be worth seeking advice from your GP on changing your method of contraception. For example, if you are on a combined oral contraceptive, it might be beneficial changing to a low dose oestrogen form or a progesterone only method, such as the Depo-Provera injection.
All that being said, if your thrush keeps coming back, it’s important to go to your GP rather than keeping on trying over the counter drugs. This is because the treatment regime for recurrent thrush is different, and will need to be taken for longer than that for simple thrush. You will also need to be tested for any underlying conditions which may be predisposing you to recurrent thrush, so it is important to go and see your doctor for advice.
Last updated May 2018
Next update due 2020
- Centers for Disease Control and Prevention, ‘Diseases Characterized by Vaginal Discharge’, 2010 STD Treatment Guidelines, 2011, [available online] https://www.cdc.gov/std/treatment/2010/vaginal-discharge.htm, (accessed 20 April 2018).
- BASHH, United Kingdom National Guideline on the Management of Vulvovaginal Candidiasis, Clinical Effectiveness Group, British Association of Sexual Health and HIV, 2007.
- D. A. Eschenbach et al., ‘Influence of the Normal Menstrual Cycle on Vaginal Tissue, Discharge, and Microflora’, Clinical Infectious Diseases, Vol. 30, No. 6, 2000, pp. 901-907.
- T. G. Bauters et al., ‘Prevalence of vulvovaginal candidiasis and susceptibility to fluconazole in women’, American Journal of Obstetrics and Gynecology, Vol. 187, No. 3, 2002, pp. 569-574.
- D. A. Eschenbach et al., ‘Influence of the Normal Menstrual Cycle on Vaginal Tissue, Discharge, and Microflora’, 2000, pp. 901-907.
- B. M. Peters et al., ‘Candida Vaginitis: When Opportunism Knocks, the Host Responds’, PLOS Pathogens, Vol. 10, No. 4, 2014.