Ethnicity is the prime factor associated with vaginal microbiome CST. Lactobacillus CSTs predominate in 80%-90% of Asian and white/Caucasian women but only account for 60%–70% of CSTS in African American or Hispanic women. This may be a reason why black women are proportionately more vulnerable to bacterial vaginosis than white women, as more black women have a mixed CST with increased microbiome diversity and reduced protective effect of lactobacilli.^1,3,11

That said, all woman’s vaginal microbiomes will fluctuate over the menstrual cycle and move more broadly over their lifetime from one CST to another, typically towards the more diverse CST type.^1,9

Practices which increase microbiome diversity such as vaginal douching may promote dysbiosis. Drugs that can affect the vaginal microbiome or cause dysbiosis include antibiotics, although dysbiosis will usually resolve after the antibiotics course ends. Copper contraceptive intra-uterine devices (IUDs) and smoking are also both associated with increased BV risk. While oral contraceptives affect hormonal levels, it is not clear whether this has an influence on BV risk.^1,12,13,14

One longer-term prospect of dysbiosis is the impact of HPV. The vaginal microbiome plays a role in resisting HPV infection with lactobacilli associated with greater protection. Vaginal dysbiosis is associated with HPV infection of types linked to increased risk of cervical cancer. HPV16 and HPV18 account for 74% of cervical cancer cases in Europe, but the UK HPV vaccination programme protects against these types.^1,4,15