Maintaining a slightly acidic vaginal pH is crucial for vaginal health as it helps to keep harmful bacteria, fungi, and viruses at bay. A high pH can disrupt the delicate balance of bacteria, leading to infections such as bacterial vaginosis, while a low pH can cause irritation and inflammation of vaginal tissues.

Some of the most common vaginal STIs include chlamydia, gonorrhea, genital herpes, syphilis, and human papillomavirus (HPV). Symptoms of vaginal STIs can vary, but may include abnormal vaginal discharge, itching or burning sensations, pain during sex or urination, and sores or lesions on the genitals.

Opportunistic bacteria can take advantage of changes in the vaginal environment, such as a decrease in acidity, to multiply and cause infections. These bacteria are normally present in small numbers in the vagina but can become problematic when their population increases. Some of the most common opportunistic bacteria of the vagina include Gardnerella vaginalis, Atopobium vaginae, and Prevotella species. They can cause bacterial vaginosis, a condition characterised by an abnormal vaginal discharge and odor.

Beneficial bacteria play an important role in maintaining vaginal health. Lactobacillus species, in particular, are the most commonly found beneficial bacteria in the vaginal microbiota. These bacteria produce lactic acid, which helps to maintain an acidic pH in the vagina, preventing overgrowth of harmful bacteria and maintaining a healthy bacterial balance.

Opportunistic fungal pathogens can cause infections in the vagina when the immune system is weakened or the vaginal microbiota is disrupted. Examples of opportunistic fungal pathogens that can cause vaginal infections include Candida albicans and Candida glabrata. These fungi normally live harmlessly in the vagina, but when there is an overgrowth, it can lead to symptoms such as itching, burning, and a thick, white discharge.

Bacterial vaginosis (BV) is a common vaginal infection caused by an imbalance of bacteria in the vaginal microbiota. In BV, the normal balance of beneficial lactobacilli and other bacteria in the vagina is disrupted, and there is an overgrowth of harmful bacteria such as Gardnerella vaginalis and Atopobium vaginae. This can lead to symptoms such as a foul-smelling discharge, itching, burning, and discomfort during sex.