Many women think they recognize the symptoms of a yeast infection—itching or stinging and discharge—yet research shows that only about one-third of those who buy over-the-counter (OTC) therapies for a yeast infection actually have one. 
Even women who have had a yeast infection confirmed by a doctor in the past have difficulty recognizing a new episode.  That's why it's important not to self-diagnose and self-treat. Making an appointment with a clinician for an examination and a test is the most effective strategy.
According to a multicenter study, only about 19 percent of women buying OTC yeast therapies actually have a diagnosis of bacterial vaginosis (a bacterial infection). Roughly 21 percent have vaginitis (a general vaginal irritation with various causes), almost 14 percent have no identifiable abnormality, 10.5 percent have other diagnoses, and a little over 2 percent have trichomonas vaginitis (a sexually transmitted infection). 
Although the symptoms of itching and discharge may be similar for all of these conditions, the treatments are not. In fact, treating for the wrong thing can often make the patient worse.
A vaginal yeast infection, also known as vulvovaginal candidiasis (VVC), is characterized by the overgrowth of a naturally occurring vaginal yeast – most commonly Candida albicans. Women are more susceptible to this in their reproductive years and at times of hormonal change, especially prior to menstruation or during pregnancy. Women who are immune-compromised—for example, those with AIDS or diabetes—are also more prone to contracting VVC. Further, women who use broad-spectrum antibiotics or corticosteroids have a high risk of developing VVC. 
About 75 percent of women will have at least one case of VVC in their lives, and that between 40 percent and 45 percent will have two or more. 
Recurrent VVC, usually defined as four or more episodes each year, affects less than 5 percent of all women with yeast vaginitis.  Contrary to popular opinion, recurrent VVC is not caused by an unusual or drug-resistant strain of yeast. In more than 90 percent of cases it is caused by the same yeast that causes initial episodes of VVC – Candida albicans.
Getting the right diagnosis
Physicians who diagnose a yeast infection without properly identifying the offending organism run the same risks of misdiagnosis as patients who self-treat. Their first tool should be pH paper that measures the acidity of the vagina. Surprisingly, this is vastly underutilized.
If a patient has a normal vaginal pH (less than 4.5), this essentially rules out bacterial vaginosis as the cause of her symptoms and suggests VVC. After that, simple microscopy can often clinch the diagnosis of VVC, but, unfortunately, this is underused, as well.
Research shows that almost 90 percent of physicians seeing women for vaginal complaints don't measure vaginal pH. Further, 40 percent fail to use a microscope to determine if yeast is present.  This means that many cases of vaginal itching and discharge are misdiagnosed and inappropriately treated.
Although recognizing organisms under the microscope can initially be challenging, getting familiar with the appearance of healthy vaginal flora can help when it comes to recognizing abnormalities.
Normal flora is characterized by rod-shaped lactobacilli and normal epithelial cells, with clear spaces between the cells, and no evidence of any other vaginal pathogens. In contrast, Candida albicans is characterized by fungal hyphae. The presence of budding yeast forms suggests non-albicans strains.
One of the stumbling blocks in diagnosing VVC comes when a patient presenting with symptoms has negative results under the microscope. This patient is a good candidate for a yeast culture. Despite negative microscopy, the yeast can show up when cultured in a lab. 
It is a common practice for many physicians to do a quick microscope evaluation, and if they fail to see yeast, they then treat for a bacterial infection. Some patients, however, may have a yeast infection that shows up only on a culture. They may be very sensitive to extremely small amounts of yeast in the vagina.
Antimicrobial treatment strategy would be inappropriate for women with yeast infections because it kills the friendly lactobacilli bacteria, which are fighting the yeast – thus making the patient's condition worse.
Women with recurrent symptoms have probably developed a hypersensitivity or allergy to yeast, and, therefore, cannot tolerate even small amounts of yeast in their vaginas.  They might also be harboring one of the more resistant Candida strains, which should be identified by culture.
The optimal treatment for patients with recurrent Candida albicans VVC remains unknown, but the accepted approach is to first attack it aggressively, and then to keep it under control with maintenance therapy.
Bear in mind that none of today's VVC therapies actually kill yeast, they simply inhibit it. The agents used to treat yeast are fungistatic and not fungicidal. These agents are not like antibiotics that kill bacteria. Thus, many women still remain culture-positive for vaginal yeast even though their symptoms have been resolved by a full course of treatment with an antifungal agent.
Candida albicans responds equally well to either the OTC preparations such as miconazole cream and suppositories (Monistat), or prescription medications such as oral fluconazole (Diflucan), or terconazole suppositories (Terazol). I prefer the oral therapy - because topical therapy can interfere with the accuracy of microscopy.
The Centers for Disease Control and Prevention (CDC) recommends 10-14 days of azole (antiyeast medications, cream or oral) therapy followed by a 6-month maintenance regimen for recurrent Candida albicans VVC.  I treat with oral fluconazole 200mg (Diflucan) every 3 days until the patient is asymptomatic, followed by a maintenance regimen involving once weekly dosing initially, gradually tapering to one dose every 2 weeks, and then every 3 weeks, as long as the patient remains asymptomatic. The treatment for resistant strains involves less commonly used oral antifungals than Diflucan.
Optimally, the patient should re-dose only once a month, just before her menstrual period when most patients tend to have a flare-up of symptoms.
For patients who have a non-albicans VVC, the CDC recommends treatment with either a longer azole (antifungal) therapy, boric acid suppositories (600mg daily for 14 days), or topical flucytosine (4 percent for 14 days). 
Although it is comforting for physician and patient to have both a diagnosis and a treatment for these symptoms, it is important to remember that many patients with vaginal itching and discharge have no identifiable disease. They may have allergies or irritations from feminine hygiene products, douches, or vaginal deodorants and should be encouraged to simply "wait it out" until their symptoms subside.
If these patients are inappropriately treated with either topical antifungal or antimicrobial agents, they often end up with complications of vulvar sensitivity and vestibulitis – something that can also be a problem in women who have had prolonged, untreated VVC.
This problem generally resolves itself once the yeast infection is eliminated or the irritant therapy is discontinued. Thus, it is very important that a proper diagnosis is made and the right treatment is started in women with yeast infections or bacterial vaginosis.
Recurrent use of over-the-counter creams and/or the wrong treatment over a period of time has the risk of leading to a hypersensitivity to yeast or a general vulvar sensitivity and vulvodynia, a burning and irritation of the vulva.
For more information about genital Candidasis, Vulvovaginal Candidiasis vaginal yeast infections (VVC), contact the CDC's Division of Bacterial and Mycotic Diseases.