Q: What causes vaginal yeast infections?

A: Candida and other yeast species are all around us. Many women have some detectable yeast in the vagina, but only some get symptoms when yeast is present. We are not sure why.

Vaginal yeast infections, also known as “yeast vaginitis” or “vaginal thrush”, occur when too much yeast grows in the vagina and causes irritation to the surrounding tissue.

You may be at a higher risk for developing yeast infections if:

  • You are taking oral antibiotics
  • You struggle to control your diabetes

As far as we know, yeast is not generally sexually transmitted. However, if your partner has symptoms, she or he should also be examined.

Q: How is a yeast infection diagnosed?

A: The symptoms of vaginal yeast infections include:

  • Vaginal itching
  • Burning with urination
  • Redness around the vagina
  • Thick, white vaginal discharge
  • Pain with sex

If you have these symptoms, you’ll need to see your health care provider to get an exam and accurate diagnosis. Self-diagnosis—based on your symptoms and a history of previous yeast infections—is wrong more than half the time, which is why we recommend getting an exam if you have symptoms.

There are three ways that vaginal yeast infections can be accurately diagnosed:

  • Examination of vaginal fluid under a microscope: this method provides immediate results, but finds yeast only about 60% of the time when it is present
  • Lab culture: a sample from the skin on your vagina is sent to the lab, where it is incubated (allowed to grow) for a few days. Then the sample is examined to identify any potential yeast. This process can take up to a week for results
  • DNA-based testing: this type of testing can be used when a lab doesn’t have the capacity to incubate yeast. It is often much more expensive, but can also identify what type of yeast is present

At Mass General, we use a combination of microscope examinations and lab cultures to diagnose a yeast infection. DNA testing is not available here.

Q: How are yeast infections treated?

A: An uncomplicated yeast infection can be treated with any one of the many available antifungal medications (both prescription and over-the-counter), which all have about the same success rate of 80-90%1. A complicated infection (one that has severe symptoms or keeps coming back, a rare strain of yeast or any infection in a diabetic or pregnant patient) will likely need longer treatment, including over a week of a vaginal cream or two to four rounds of an oral medication.

If you have a more rare kind of yeast, your health care provider may also prescribe vaginal boric acid suppositories, which are specially made in a compounding pharmacy and used every night for 7-14 days.

Q: Can I receive a prescription for treatment over the phone?

A: Vaginal symptoms are often misdiagnosed at home. Because of this, we generally like to see you to confirm that your symptoms are actually from yeast. If you have recurrent yeast problems, this can also cause your vulva to become sensitive and easily irritated, making it hard to know if your symptoms are an infection or merely inflammation.

Q: How can I prevent future yeast infections after I finish treatment?

A: There are a number of things you can to do help prevent yeast infections. If you have fewer than four yeast infections in a year, you should:

  • Avoid unnecessary antibiotic use
  • Change out of wet, tight clothes as soon as possible

If you have four or more infections a year that have been proven by exam or culture, a weekly dose of an oral medication for six months can help prevent recurrence.

Q: Is hormonal birth control associated with yeast infections?

A: Some studies have shown an increased risk of yeast in women using oral birth control pills, but no one has studied whether that risk decreases if you stop using the pill. We do not recommend stopping your birth control method because of recurrent yeast infections unless you have first made an alternative plan for pregnancy prevention.

Q: What about the other treatments I have heard about for yeast infections? Do they work?

A: Yogurt: Variable data exist. One small study2 of 33 women showed a decrease in yeast colonization of the vagina when women ate 8 oz. of yogurt containing L. acidophilus each day.  A second study3 of 46 women showed no difference. 

  • The verdict: Probably can’t hurt, as long as you like yogurt.

Probiotics: Most probiotics contain Lactobacillus bacteria, which are common in a healthy vagina. However, the most common vaginal bacteria that are present when we diagnose yeast in a woman are Lactobacillus. While some strains of Lactobacillus kill yeast in the lab, we don’t think this happens in the vagina. Probiotics are not regulated by the Food & Drug Administration (FDA), and other studies have shown that many products either do not contain the bacterial species described on the label or do not contain the same amount as described on the label.

  • The verdict: There is little data to support probiotic use. 

Garlic: Allicin, a compound extracted from garlic, has been found to kill yeast in the lab and in animal studies. A recent, small study4 of oral garlic pills (Garlicin™, three tablets, twice daily) did not show a reduction in vaginal yeast colonization. No one has studied vaginal garlic, and some patients have reported that this can cause vaginal burning.

  • The verdict: Even when using oral pills, it is unlikely you can put enough raw garlic in the vagina to reach the levels of allicin that are effective in the lab.

Cutting out sugar or bread: The impact of changing your diet on yeast levels has not been well studied. We do know that diabetes is associated with yeast infections, and a small study showed that women with recurrent yeast infections have higher blood glucose levels after taking a high-sugar drink. However, we do not know if cutting out sugar altogether decreases yeast infections.

  • The verdict: In general, it isn’t recommended that you cut out any particular food groups. It is a good idea to eat a healthy, balanced diet with lots of vegetables, whole grains and few processed carbohydrates.

Tea tree oil douches or pessaries: Although tea tree oil works very well in the lab to kill yeast, in clinical practice it has been known to cause terrible skin reactions on the vulva.

  • The verdict: This is not recommended. 

Herbal extracts: There are plenty of different herbal options available in stores. However, none have been studied in randomized trials, and none are regulated by the FDA. 

  • The verdict: We don’t recommend any of these products, as many herbal products can cause more irritation than improvement.

The bottom line: Yeast infections happen. If you think you may have a yeast infection, it is reasonable to try a single course of over-the-counter treatment, but if that doesn’t work, or if it makes your symptoms worse, contact your health care provider for guidance on treatment. 


  1. CDC 2015 Sexually Transmitted Diseases Treatment Guidelines.
  2. Hu H, Merenstein DJ, Wang C, Hamilton PR, Blackmon ML, Chen H, Calderone RA, Li D. Impact of eating probiotic yogurt on colonization by Candida species of the oral and vaginal mucosa in HIV-infected and HIV-uninfected women. Mycopathologia. 2013 Oct;176(3-4):175-81.
  3. Shalev E, Battino S, Weiner E, Colodner R, Keness Y. Ingestion of yogurt containing Lactobacillus acidophilus compared with pasteurized yogurt as prophylaxis for recurrent candidal vaginitis and bacterial vaginosis. Archives of Family Medicine. 1996 Nov-Dec;5(10):593-6.
  4. Watson CJ, Grando D, Fairley CK, Chondros P, Garland SM, Myers SP, Pirotta M. The effects of oral garlic on vaginal candida colony counts: a randomised placebo controlled double-blind trial. BJOG: An International Journal of Obstetrics & Gynaecology. 2014 Mar;121(4):498-506.