Vulvovaginal candidiasis (VVC) or thrush is the second most common cause of vaginal infection and is caused by Candida yeasts. Three quarters of women will have at least one episode of VVC in their lifetime, but around 6% – about 1.2 million women in the UK – have recurrent VVC, that is having four or more episodes in the past 12 months.^23,24,25

Candida species are normally present in low levels on the skin, in the gut and in mucus membranes including female genitalia. Over 20 Candida species can cause infections, but C. albicans is the most likely, accounting for 80-90% of VVC. One in five women of reproductive age may be colonised with Candida spp but have no symptoms and do not require treatment.^24,26

Thrush can result from dysbiosis due to taking antibiotics or oral contraceptives, or using HRT, poorly controlled diabetes mellitus, and immunosuppression. Hormonal changes in pregnancy can trigger thrush, particularly in the third trimester, but it is not thought to put the unborn child at risk.^24,26

Allergy, such as allergic rhinitis and asthma, may be linked to recurrent VVC due to neutrophil infiltration, although corticosteroid use may also be a factor. Chronic stress, with an effect on cortisol levels, may be weakly associated with VVC, but evidence is limited. Nutritional status is another possibility, with reduced levels of particularly iron, but also zinc, magnesium or calcium deficiency suggested as potential risk factors.^24,28