Hi,
Yeast is probably present in our body (e.g. in the gut) from a baby onwards.It normally co-exists with other bacteria (which is beneficial for our body) and does not create any problems unless we become immune deficient.
For women, it probably starts to reside in the vagina from puberty (or even earlier) onwards, because the hormonal changes creates an environment suitable for its growth.
Vaginal yeast infections are a result of its overgrowth (relative to the balance against the good bacteria) . They can be very common and do not cause any permanent damage. It can cause local itch and irritation, leading to symptoms of whitish discharge, discomfort and soreness.
Use of antibiotics (which can reduce the good bacteria in our body too), a high sugar level in our bodies and hormonal changes are some of the factors which alter the population of yeast and lead to "infection".
You can consult with your doctor to explore ways to reduce the chance of recurrent yeast infections.
Best regards
Dr Fong Yoke Fai