ANN ARBOR—Two out of three women experience the itching, burning, soreness and discharge of vulvo-vaginal Candidiasis, or vaginal yeast infection, at least once in their lives, but surprisingly little is known about what women can do to prevent themselves from getting this common condition.

A University of Michigan School of Public Health study of 691 women is the first population-based study specifically designed to identify risk factors for yeast infections. The researchers also tested whether commonly suspected factors increase the risk and found that some were not significant after all. The researchers gathered data through clinic records and a survey.

The researchers—Betsy Foxman, associate professor of epidemiology at U-M, and Ann M. Geiger, now a researcher at Kaiser Permanente, Southern California—published their study in the March issue of Epidemiology.

The risk factors included:

–Receptive oral sex. ” Participation in oral sex tripled the risk,” said Geiger. ” Oral sex may provide a route for transmission of yeast, as one-third to one-half of adults carry yeast in their oral cavity. Saliva could also cause irritation, facilitating Candida adherence and growth.”

–Oral contraceptive and spermicide use within the last two weeks. ” Risk for a yeast infection was doubled by use of oral contraceptives and tripled by spermicides,” said Foxman.

–Having been diagnosed with a yeast infection within the past year tripled or quadrupled the risk. ” This may reflect a lengthy alteration of the vaginal microenvironment that results in increased susceptibility,” Foxman said.

–Being young. ” In this study, women younger than age 24 had a 75 percent increased risk of developing a yeast infection. It may be that young women have a constellation of sexual, hygiene and other behaviors that make them more vulnerable, or it may be that older women are more resistant,” said Geiger. ” Or older women may be more likely to know what they have and self- treat.”

Women with yeast infections were also more likely to be non- white. ” Since this is the first report of racial differences in occurrences of yeast infections, we are uncertain whether this reflects differences in use of medical services or unmeasured behavioral factors. We know of no research suggesting physiologic differences resulting in heightened susceptibility,” Geiger added.

Surprisingly, recent antibiotic use, type of underwear worn, menstrual habits, and use of feminine hygiene products had little or no effect on the development of Candidiasis. Vaginal intercourse, masturbation and the number of sexual partners also were not associated with the ailment.

Approximately $600 million is spent annually in the United States on the diagnosis and treatment of yeast infections and sales of over the counter vaginal antifungals was projected to be as high as $800 million in 1995.