Every woman has yeast organisms in her vagina naturally. But sometimes, yeast grows too much and causes an infection. This can happen for different reasons. Sometimes, antibiotics--medicine taken for infections--can actually cause a yeast infection (also known as thrush). That's because some antibiotics kill the "good" bacteria that keep other yeast from growing too much.

Changes in your hormone levels--either from pregnancy or taking birth control pills--can also start yeast infections. Diabetes, which allows too much sugar in the urine and vagina, can also be a cause. And a girl can get a yeast infection if her vulva is damp from staying in a wet bathing suit or exercise clothes for a long time.

Some girls get yeast infections more than others. To reduce the chances of getting one, avoid wearing tight pants, non-cotton underwear, and staying in wet clothes (a bathing suit or sweaty exercise clothes) for too long.

Usually, the first symptom of a yeast infection is redness and itching around the vulva and inside the vagina. There can also be white, thick, clumpy discharge that looks like cottage cheese. The vulva can be sore, too, or it may hurt to pee.

If you think you have a yeast infection, see your doctor or health care provider. These infections are usually treated with antifungal creams or suppositories (medicine inserted into the vagina). This medicine can be bought without a prescription at most drugstores or supermarkets. Avoid having sex during a yeast infection, since it can affect your partner's body and the medicine can weaken latex.

Often, if you have a yeast infection, your partner also has it (male or female partners). They will also need to be treated so that you don't pass it back and forth to each other. If your partner has given you oral sex when you have a yeast infection, it is possible for them to develop yeast in their mouth, called thrush. This is also easily treatable.

If you keep getting yeast infections, it could be a sign of more serious problems, including HIV, the virus that causes AIDS. Talk to your doctor or health care provider.

For more information, you can do a search for "yeast infections" on WebMDHealth.