The candida cells, which are relatively benign in their yeast form, adopt their fungal form and begin to grow hyphae – the long branches that grow out of the fungus. These branches invade the cells in your intestinal lining and creating inflammation.

Vaginal flora and pH levels

A healthy vaginal flora protects the body against urogenital infections. It is made up of many different types of probiotic bacteria, the predominant bacteria being lactobacilli. Indeed, these lactobacilli and candida species often co‐exist in the vagina of healthy women.

Lactobacilli protect against vaginal infection simply by colonizing the space available. They build up a barrier against candidal overgrowth by blocking the adhesion of candidal yeast cells to vaginal epithelial cells, through competition for nutrients. They also produce lactic acid and hydrogen peroxide. Lactic acid helps to maintain a healthy vaginal pH and flora. Hydrogen peroxide stops the overgrowth of ‘bad’ bacteria that cause infection. When the level of lactobacilli is disrupted and the vaginal flora becomes imbalanced, the risk of developing an infection is increased. The infections can lead to unpleasant symptoms such as itching, irritation, burning, abnormal discharge and unpleasant vaginal odour.

The balance between beneficial and harmful bacteria in the vagina is very fragile, an imbalance occurs if the vaginal pH is not acidic enough. The vagina pH should be somewhere between 3.8 and 4.5 for a healthy level of vaginal acidity. If the vagina is not acidic enough due to a shortage of lactobacilli, then fungi and ‘bad’ bacteria are able to reproduce more than they usually would.

Antibiotic treatment for a UTI can affect the vaginal flora. Two examples of infection that arise in this way are thrush (caused by overgrowth of the fungus Candida) and bacterial vaginosis (caused by overgrowth of ‘bad’ bacteria).

The role of oestrogen

Interestingly, oestrogen levels are important for the maintenance of vaginal pH. Thrush spores are noted to be at their highest during the latter half of a women’s monthly cycle when oestrogen levels are lower because the vaginal pH balance has become more alkaline. Thrush can affect women on low oestrogen birth control or when they enter peri, menopause or become post menopausal. This is again because of the loss of oestrogen.

Localised oestrogen therapy can help restore levels within the vagina and may help with the control of outbreaks of thrush.

However, too much oestrogen may encourage candida cells to multiply. A study published in the American Society of Microbiology in 2006 found, if certain types of oestradiol (a specific type of oestrogen found in birth control pills or hormone replacement therapies) are added to candida cells, this oestrogen has been shown to increase the number of germ tube and length – developments that support candida overgrowth.

Oestrogen also acts on Candida yeasts and promotes its growth, and improves its ability to cling onto vaginal epithelial cells as shown by this study published in PLoS Pathogens in 2014.

These changes together may encourage the overgrowth of Candida, and further studies are being conducted to gain a better understanding of these mechanisms.