About three-quarters of women will get at least one vaginal yeast infection in their lifetime. It happens when a fungus called Candida, which normally lives in small amounts inside the vagina, grows out of control. The vagina has a built-in defense system that keeps Candida in check, but several common triggers can throw that system off balance.
What Keeps Yeast Under Control
Your vagina is home to a community of beneficial bacteria, primarily a species called Lactobacillus. These bacteria do two important things: they produce acid that keeps the vaginal pH between 3.8 and 4.5, and they physically occupy space on the vaginal walls, blocking yeast from attaching and spreading. Think of them as a living barrier.
As long as this bacterial community is thriving and your immune system is functioning normally, Candida stays in its harmless yeast form. When something disrupts that ecosystem, Candida can shift into an aggressive form that sends root-like filaments into vaginal tissue, causing the itching, burning, and discharge that characterize a yeast infection. The vaginal pH during a yeast infection typically stays in the normal range (4 to 4.5), which is one reason it can be tricky to distinguish from other vaginal infections without a proper exam.
Antibiotics Are the Most Common Trigger
Broad-spectrum antibiotics are one of the best-documented causes of yeast infections. These medications don’t just kill the bacteria making you sick. They also wipe out the Lactobacillus that protect your vagina. With that bacterial barrier gone, Candida has open real estate to multiply. The longer the course of antibiotics and the broader their spectrum, the greater the risk. Even antibiotics prescribed for something completely unrelated to your reproductive system, like a sinus infection or acne, can set off a vaginal yeast infection.
Hormonal Changes That Fuel Yeast Growth
Estrogen plays a direct role in yeast infection risk. High estrogen levels increase the amount of glycogen (a type of sugar) stored in vaginal cells, which creates a richer food source for both beneficial bacteria and yeast. When estrogen surges, the extra glycogen can tip the balance in favor of Candida overgrowth.
This is why yeast infections are more common during pregnancy, when estrogen levels are significantly elevated. Women on combination birth control pills or hormone replacement therapy with estrogen also report more frequent infections. On the flip side, after menopause, dropping estrogen levels cause vaginal cells to lose glycogen. The beneficial bacteria that depend on glycogen for food decline, which can also leave the door open for yeast. Women placed on vaginal estrogen therapy for menopause symptoms sometimes notice a return of yeast infections for the same reason: the estrogen feeds the cycle again.
Blood Sugar and Diabetes
Poorly controlled blood sugar is a well-established risk factor. When glucose levels in your blood run high, excess sugar shows up in vaginal secretions and urine. Yeast thrives on sugar, so this creates an ideal growth environment. Women with type 2 diabetes who have difficulty managing their blood sugar are particularly vulnerable to recurring infections. Getting blood sugar under tighter control often reduces the frequency of yeast infections significantly.
A Weakened Immune System
Your immune system actively monitors Candida and keeps its population small. Anything that suppresses immune function can allow yeast to proliferate. HIV/AIDS, cancer treatment, chemotherapy, and long-term use of corticosteroids (including inhaled steroids for asthma) all increase the risk of Candida overgrowth. Even high stress or poor sleep over extended periods can impair immune responses enough to make infections more likely.
Hygiene Products That Backfire
Douching is one of the most counterproductive things you can do to your vaginal health. It strips away the normal bacteria that maintain the acidic environment, directly enabling yeast and harmful bacteria to take over. The vagina is self-cleaning, and introducing water, vinegar, or commercial douching solutions disrupts the very ecosystem that prevents infections.
Scented tampons, pads, powders, and sprays pose a similar problem. The chemicals in fragranced products can irritate vaginal tissue and alter the bacterial balance. Unscented, simple products are a safer choice.
Clothing and Moisture
Candida grows best in warm, moist environments. Tight, non-breathable clothing, especially synthetic underwear or workout leggings worn for hours, traps heat and moisture against the vulva. The CDC specifically recommends cotton underwear and breathable, loose-fitting clothing as a preventive measure. Sitting in a wet bathing suit or sweaty gym clothes for extended periods creates the same problem. Changing into dry clothes promptly after swimming or exercise reduces the window of opportunity for yeast.
Why Some Women Get Recurring Infections
Around 10% of women who get yeast infections develop a recurring pattern, typically defined as four or more episodes per year. For many of these women, the triggers aren’t always obvious. The interaction between Candida, the vaginal immune response, and the bacterial ecosystem is complex, and researchers still don’t fully understand why some women’s bodies repeatedly fail to keep the fungus in check.
What is clear is that recurring infections aren’t simply a hygiene issue. They often involve a combination of genetic susceptibility, hormonal patterns, and shifts in the vaginal microbiome that make certain women’s bodies more hospitable to Candida. Even with appropriate treatment, at least half of women with recurrent infections experience a relapse once treatment stops, which points to underlying factors beyond just the immediate trigger.
Reducing Your Risk
You can’t eliminate every risk factor, but several practical steps lower the odds. Avoid douching entirely. Choose cotton underwear and change out of wet or sweaty clothing quickly. If you’re prescribed antibiotics, be aware that a yeast infection may follow, and talk to your provider about whether a preventive antifungal makes sense. If you have diabetes, keeping blood sugar well controlled is one of the most effective things you can do.
Skip scented products in the vaginal area. Use mild, unscented soap on the external vulva only, and let the vagina handle its own internal cleaning. If you’re on hormonal contraception and noticing frequent yeast infections, a different formulation with lower estrogen may help.