How Your Immune System Influences Recurrent Thrush

Written by Gemma McLeod (BNatMed, mNMHNZ)
Clinical Naturopath at Ovela Health

What makes recurrent thrush different?

Around 75% of women will experience at least one episode of thrush in their lifetime. For 5-10% of those women, it doesn’t stop there, and they go on to develop recurrent vulvovaginal candidiasis (RVVC), which is defined as four or more episodes of vaginal thrush in a year.

What is different about that 5-10%? Part of the answer may lie within the immune system.

Immune responses to Candida

For your immune system to fight Candida albicans (the fungus that most often causes thrush), it first has to recognise it as a problem. It does this through special ‘sensors’ on immune cells, including Toll-like receptors such as TLR2. In mouse studies, animals lacking TLR2 had heavier fungal growth in the vagina, deeper tissue invasion, and more inflammation. Human studies show something similar: women with a certain genetic variation in the TLR2 receptor are about three times more likely to experience recurrent thrush, because their immune system is less effective at recognising Candida and switching on the antifungal defences needed to keep it under control.

The role of the vaginal lining (epithelium)

Vaginal epithelial cells (cells that line the vagina) are the first line of defence against vaginal thrush.

Studies show that the vaginal epithelial cells from healthy women are more effective at hindering the growth of Candida albicans than vaginal epithelial cells from women with RVVC. So what is going on here?

Again – we have the immune system to thank for this. The cells lining a healthy vagina can recognise and control Candida in stages – holding it in balance when it’s at low levels and not causing trouble (commensal), but stepping up defences if it tries to invade (by making hyphae or multiplying too much). In women with recurrent thrush, this frontline defence doesn’t work as well.

Hormones and the immune response

When looking at how oestradiol and progesterone influenced the movement of neutrophils (immune “first responder” cells) into the vagina during Candida infection, researchers found that progesterone improved neutrophil migration into the vagina and subsequent Candida clearance, while oestrogen elicited a much slower response and did not clear Candida.

In clinic, I often see women with recurrent thrush experience flare-ups in the luteal phase of their cycle. Blood tests frequently show a picture of relative oestrogen dominance. While this isn’t the only factor, it may help explain why infections are more likely at this time.

Get help for recurrent thrush

If you’re wondering why thrush keeps coming back, I hope this post has given you some clarity on how your immune system, hormones, and vaginal environment all play a role. Lasting change often means addressing these factors together. If you’re ready to get to the root cause with tailored support, you can book a consultation. Or, if you’d prefer to begin with simple, evidence-based options, explore Ovela’s vaginal health range.