Lactobacilli are lactic acid bacteria that are found in the human body, in particular the vagina and intestine. Lactobacilli help protect the fragile bacterial flora colonising healthy vaginas. When there are sufficient levels of lactobacilli, they maintain optimal pH levels by inhibiting the growth of pathogenic germs and fungi.

They secrete substances such as hydrogen peroxide and lactic acid that boost local immune defences by slowing the development of harmful microbes and preventing them from attaching to vaginal mucosa.