Many women will struggle with vulvovaginal candidiasis (thrush) at some point in their lives. Candida is simply a type of yeast cell, of which there are many subtypes, any of which can cause a fungal infection anywhere in the body. In most places this occurs only rarely and when there is immune system dysfunction.
Vaginal and vulval Candida infections are quite common however; studies show that between 29% and 49% of women have had thrush, with 10% of women suffering from recurrent thrush.1 Yeast is a normal constituent of the vaginal flora, and under normal conditions its growth is constrained by other bacteria and fungal cells all competing for the same space and energy resources. This may sound disturbing but it shouldn’t be – I remember my surprise in medical school on discovering that we have ten bacterial cells within our body for every human cell we carry.
Under positive conditions yeast cells multiply and kill off their competitors, causing irritation, inflammation, intense itch, and discharge which is classically described as having the consistency of cottage cheese. For many women this is a source of embarrassment and also the loss of sexual confidence. Effective antifungals are available over the counter, but recurrence of thrush is common and resistance to antifungals can occur, so naturally many women explore alternative means to treat their thrush. But do these natural remedies actually work?
Boric acid is a weak acid available usually as a pessary (an insertable, dissolvable pill) as a treatment for thrush. Like any living cell, yeast carries enzymes to speed up the chemical reactions that keep it alive, and these enzymes are exquisitely sensitive to the acidity of their environment. Boric acid disrupts this environment, destroying yeast enzymes and killing the cells off. A systematic review of all studies comparing boric acid to conventional treatments found that boric acid is a safe and effective alternative treatment for women with chronic thrush when conventional treatment fails, working in 40-100% of cases depending on the study.2 Unsurprisingly, as an acid, this therapy can cause temporary irritation, burning sensations, watery discharge and redness to the applied area. Typically an effective treatment course runs from one to two weeks.
Tea tree oil-
Tea tree oil is an essential oil extracted by using steam to evaporate and distil the liquid held within the tea tree (Myrtaceae tree) native to Australia and long used in traditional medicine. In the lab it has been shown to destabilise the cell membrane (envelope) within which bacteria and fungi live, creating holes for vital cell organs to seep out of.3 There is less promising evidence for other such oils. Good evidence for the use of tea tree oil in animal models has been demonstrated: when rodent models were infected with drug-resistant Candida, tea tree oil was highly effective in accelerating thrush clearance.4 Animal models are not totally reliable evidence, but this remains a promising area to watch for future research. Side effects such as allergic reactions, skin irritation, burning, and localised skin redness have been reported.
In healthy women, lactobacillus is ideally the predominant bacterium of the flora in the vaginal tract. An imbalance in this microbiome can predispose women to fungal infection; lactobacillus bacteria create a naturally acidic pH in the reproductive tract which helps to ward off infection, theoretically similar to the boric acid treatment already discussed. It has been theorised that eating yoghurt rich in lactobacilli or even directly applying it vaginally may rectify this imbalance. The evidence for these approaches is poor; many studies are poorly designed and funded by the probiotic industry, valued at seven hundred and fifty million pounds a year in the UK. There is some (limited) evidence for probiotic use in irritable bowel disease and infective diarrhoea, but not for vaginal thrush, so save your money. Any substance containing sugar is also a good environment for (unhealthy) bacteria to replicate, so topical use of yoghurt can result in urinary tract infection.