Vulvovaginal Candidiasis (Yeast Infection)
Vulvovaginal candidiasis (VVC) is a common vaginal infection caused by species of Candida yeast. These are normal inhabitants of the vaginal microbiome, but certain contraceptives, conditions, and behaviors can disrupt the vaginal environment and lead to an overgrowth.
VVC (commonly referred to as a yeast infection) is a common vaginal fungal infection caused by the overgrowth of Candida species (most often C. albicans). An estimated 70%–75% of women experience one episode of VVC in their lifetime, and 5%–8% of women are affected by recurrent VVC (defined as four or more episodes in one year).
Uncomplicated VVC infections are generally infrequent, mild-to-moderate in severity, occur in women with normal immune function, and resolve with treatment because they're most often caused by the antifungal-sensitive species C. albicans. Complicated VVC, however, is characterized by severe, recurrent episodes that occur in women with diseases that increase their risk of infection and are caused Candida species that are harder to treat.
The most common sign of VVC is an abnormal discharge that may be thick or watery and resembles cottage cheese. Unlike other vaginal infections, this discharge isn’t associated with a strong odor, and vaginal pH is normal. Symptoms may include vaginal or vulvar itching, irritation, soreness, redness, swelling, and burning sensations, but VVC can also be asymptomatic.
After performing a medical examination of the vulva and vagina, a medical practitioner will collect a sample of vaginal discharge to observe under a microscope, which allows them to apply a specific solution that makes it possible to see hyphal Candida (the form in which they can cause disease).
If a woman has symptoms of VVC but the microscopy doesn’t reveal any Candida, another sample may be applied to a cell culture plate that promotes microbial growth, and if Candida are present, they will be observable in a few days.
Antifungal drugs, which work by changing the permeability of the fungal cell membrane, are the most effective treatment option for VVC. Both oral and topical antifungal medications treat the symptoms of VVC, but topical antifungals are more effective at reducing Candida colonization and are also available without a prescription.
The most widely used antifungal drugs are azoles, such as ketoconazole and fluconazole (both of which are available over the counter). Prescription antifungal drugs may be more effective for infections caused by species other than C. albicans.
A number of other topical or suppository supplements have also been studied alone or in combination with antifungal treatments, including yogurt, honey, boric acid, ginger, and curcumin. Though some treatments were more effective than placebo and appeared comparable to antifungal treatments, many of the trials have considerable limitations.
The presence of oral probiotics and food-based microbes in stool and vaginal samples indicate that ingested microbes can be transferred to the vagina (likely due to its proximity to the rectum). In a few small studies, some women exhibited lower Candida colonization and had fewer episodes of VVC after eating yogurt each day for several months, but these results were inconsistent.
Limited evidence suggests that diets low in sugary foods and beverages could be a protective factor, but without controlling for other variables, no firm conclusions can be drawn about the relationship between dietary sugar intake and VVC.
One study found that undergarments made of cotton or medical-grade silk infused with an antimicrobial compound improved the symptoms and recurrence of yeast infections in women receiving antifungal treatment. 
Under normal circumstances, Lactobacilli bacteria are dominant microbes of the vaginal microbiome, but there are a number of factors that can disrupt the balance and provide Candida with an opportunity to multiply, including hormonal changes during puberty or pregnancy, uncontrolled diabetes, immunosuppression, and the overuse of antibiotics.
Weaker evidence suggests that other behaviors could also increase the risk of VVC, such as the use of estrogen-containing oral contraceptives, spermicides, douching, and frequently wearing tight, synthetic pants or undergarments (e.g., leggings, damp swimsuits).
VVC isn’t a sexually-transmitted disease (because it isn’t contracted exclusively through sexual activity) but it may be possible to contract it from a sexual partner. Condoms and hygienic sexual practices (like washing both sex toys and the external genitalia before and after sexual activity) can help prevent VVC from occurring by reducing the transfer of abnormal (or fecal) microbiota into the vagina.