Seventy-five percent of all women have had yeast infections at some point, and nearly half have had more than one. It's no wonder there are so many TV ads for yeast infection treatments.

The most common yeast infections are caused by a strain of microscopic fungi called Candida albicans. It's normal to have small amounts of this fungi in the vagina, but changes in a woman's body can lead to an overgrowth. This may happen when you take oral antibiotics, or oral contraceptives with high estrogen levels. Damp, snug clothing, like a wet bathing suit or tight jeans, can also lead to infection. Symptoms of yeast infection include itching, irritation, and redness around the vagina; a thick, white or yellow vaginal discharge; vaginal burning or pain during urination or sex; and odor.

Before you head to the pharmacy...

A number of creams or vaginal suppositories are available over the counter to treat yeast infections. Talk to your doctor before you take any medicine, especially if your symptoms are occurring for the first time. More than half of women who treat themselves for what they think is a yeast infection actually have something else. A doctor can determine the cause of your symptoms by taking a swab sample for a yeast culture test. He or she may then prescribe either a topical cream or an oral medication.

When it's not a yeast infection, it could be. . .

• Bacterial vaginosis, caused by an overgrowth of bacteria. More common than a yeast infection, it is usually treated with prescription antibiotics.
• Trichomoniasis, which is transmitted sexually and often treated with the antibiotic Metronidazole.
• Chlamydia vaginitis and urethritis, a common infection of the cervix, is primarily sexually transmitted and most common in women 18 to 35 who have more than one sexual partner.
• Noninfectious vaginitis. Some women experience the symptoms of a yeast infection without an infection. They may have an allergic reaction to vaginal or spermicidal products or sensitivity to perfumed soaps or detergents.