Vaginal yeast infections, also called Candida vaginal infections or candidiasis, are common and easily treated in most women. They are usually caused by an overgrowth of a fungus (genus: Candida) that lives in the body. Candida is always present in the vagina, mouth and gastrointestinal tract in small amounts, and normally it is kept in check by the body's own resistance and competition with other beneficial organisms. However, when an imbalance occurs, Candida can multiply and symptoms of candidiasis appear. It is unclear whether yeast infections are sexually transmitted, according to the National Institute of Allergy and Infectious Diseases (NIADD).

During a lifetime, 75 percent of all women are likely to have at least one vaginal Candida infection, and up to 45 percent have two or more. Vaginal yeast infections are the second most common cause of cases of abnormal vaginal discharge in the United States (the first is bacterial vaginosis). Women tend to be more susceptible to vaginal yeast infections if their bodies are under stress due to poor diet, illness, lack of sleep and when they are taking antibiotics or corticosteroid medications. Occasionally, a yeast infection may be an early sign of diabetes.

Yeast infections may be more common around the time of a menstrual period. In a normal menstrual cycle, estrogen deposits glycogen (a form of sugar) in the cells that are found in the lining of the vagina. The release of progesterone causes the cells to shed into the vagina, so the sugar becomes available for yeast to feed on, multiply and grow. Estrogen and sugar production peak at the midpoint between periods, and then progesterone begins to build and sugar is released. Yeast infection symptoms can follow the hormonal pattern of this cycle. Usually, the most severe symptoms occur before the onset of a woman's period when more sugar is available. During and after the flow, symptoms are likely to subside. Additionally, changes in the vaginal pH can disrupt the immune system or destroy the so-called friendly bacteria that populate the vaginal canal and keep the yeast fungus in check.

Yeast infections are quite common during pregnancy, perhaps due to a chemical change in the vaginal environment — essentially there is more sugar in the vaginal secretions on which the yeast can feed. Similarly, people with diabetes also get yeast infections more frequently. In addition, wearing tight or synthetic clothing that traps heat and moisture and doesn’t permit sufficient air circulation to allow the area to dry may increase your risk. On rare occasions, men may also experience genital candidiasis, which can be difficult to distinguish from another type of fungal infection common in some men: dermatophyte infection (jock rot). This sort of infection may be passed between sexual partners even though it is not usually considered a sexually transmitted disease, or STD.

About five percent of women with vaginal yeast infections develop recurrent vulvovaginal candidiasis (RVVC), which is defined as four or more symptomatic vaginal yeast infections in a one-year period. Although RVVC is more common in women who have diabetes or weakened immune systems, most women with RVVC have no underlying medical illness that would predispose them to recurrent infections. Some women may have a lack of resistance to Candida that allows repeat yeast infections to occur.

Copyright 2003 National Women's Health Resource Center Inc. (NWHRC)