Candida albicans is the most common STD caused by yeast. The tip and/or foreskin of the penis, the anus or vaginal mucous membrane may be reddened, burning, itching; it is covered by a whitish layer, a watery white discharge (from the vagina or anus) may be present. Yeasts often flourish and cause problems after the prolonged use of antibiotics or in diabetics. They are mostly treated by an appropriate ointment; and medication in the form of pills may also be prescribed.