Yeast infections are caused by an overgrowth of a fungus called Candida that naturally lives in your body. About 75% of women develop at least one vaginal yeast infection in their lifetime. The fungus is normally kept in check by beneficial bacteria and your immune system, but when that balance gets disrupted, Candida multiplies rapidly and causes symptoms like itching, burning, and thick discharge.
Understanding what tips that balance helps explain why yeast infections happen, and more importantly, what makes some people prone to getting them repeatedly.
What Happens Inside Your Body
Candida, most commonly a species called Candida albicans, lives on your skin and mucous membranes without causing problems. In the vagina, it coexists with a community of beneficial bacteria, primarily Lactobacillus species. These bacteria produce lactic acid and other compounds that keep the vaginal environment slightly acidic (around pH 3.8 to 4.5), which suppresses Candida growth. The bacteria also physically block yeast from latching onto vaginal tissue and secrete substances that directly inhibit fungal activity.
When something disrupts this microbial community, Candida seizes the opportunity. The fungus shifts from its harmless round yeast form into an invasive form with long, branching filaments called hyphae. This shape change is one of Candida’s most important tricks: the filaments burrow into the lining of vaginal tissue, resist the immune system’s attempts to engulf them, and cause the inflammation and irritation you feel as symptoms. It’s not that you “catch” Candida from somewhere. It’s already there, waiting for the right conditions.
Antibiotics Are the Most Common Trigger
Broad-spectrum antibiotics are one of the most frequent causes of yeast infections. These medications are designed to kill harmful bacteria, but they also wipe out the protective Lactobacillus in your vagina. Without those bacteria maintaining an acidic environment and producing anti-fungal compounds, Candida can grow unchecked. The longer the course of antibiotics, the greater the disruption. This is why many women develop a yeast infection during or shortly after finishing a round of antibiotics for a completely unrelated issue like a sinus infection or urinary tract infection.
How Hormones Play a Role
Estrogen has a direct effect on the vaginal environment. It promotes the buildup of glycogen (a stored sugar) in the cells lining your vagina. Lactobacillus bacteria feed on this glycogen to survive and produce the lactic acid that keeps Candida suppressed. When estrogen levels are high, as during pregnancy or while taking certain birth control pills, glycogen levels rise significantly. This can shift conditions in favor of yeast growth, which is why pregnant women are especially susceptible.
The relationship works in the opposite direction too. During and after menopause, estrogen drops sharply. The vaginal lining thins, glycogen decreases, and Lactobacillus populations decline because they’ve lost their food source. With fewer protective bacteria, the vagina becomes more vulnerable to overgrowth by yeast and other organisms. Hormone replacement therapy can sometimes restore this balance, but the hormonal shifts themselves create windows of vulnerability.
Blood Sugar and Diabetes
High blood sugar creates a favorable environment for Candida throughout the body. When blood glucose stays elevated, excess sugar can appear in vaginal secretions and urine, essentially feeding the yeast. Women with diabetes, particularly those whose blood sugar is poorly controlled, face a significantly higher risk of yeast infections. The CDC identifies recurrent yeast infections as a notable concern for women with diabetes.
Even without a diabetes diagnosis, consistently high sugar intake may contribute. Yeast thrives on simple sugars, and some healthcare providers recommend reducing refined sugar and processed carbohydrates as part of managing recurrent infections. The evidence on diet alone is not as strong as the evidence for blood sugar control in diabetes, but the biological logic is straightforward: more available sugar means more fuel for Candida.
Immune System and Other Medical Factors
Your immune system is the other major line of defense against Candida overgrowth. Anything that weakens immune function raises your risk. This includes HIV/AIDS, immunosuppressive medications taken after organ transplants, chemotherapy, and chronic stress or sleep deprivation that wear down immune responses over time. In a healthy immune system, white blood cells recognize early Candida overgrowth and keep it contained. When that surveillance falters, the fungus can transition to its invasive form more easily.
Hygiene Products That Backfire
Douching is one of the clearest lifestyle risk factors. The practice of flushing water or cleaning solutions into the vagina disrupts the natural bacterial balance and can directly cause yeast overgrowth. The Office on Women’s Health advises against douching entirely, noting it can lead to both yeast infections and bacterial vaginosis.
Scented tampons, pads, powders, and vaginal sprays carry similar risks. These products can irritate vaginal tissue and alter the chemical environment that keeps Candida in check. The vagina is self-cleaning, and introducing fragrances or chemicals does more harm than good. Wearing tight, non-breathable clothing or staying in wet swimwear for long periods also creates the warm, moist conditions where yeast flourishes.
Why Some People Get Them Repeatedly
Recurrent yeast infections, defined as three or more episodes within a single year, affect fewer than 5% of women. For these individuals, the causes are often layered. Ongoing antibiotic use for a chronic condition, poorly managed diabetes, hormonal fluctuations, and genetic differences in immune response can all overlap to create a cycle of infection. Some women carry Candida strains that are more aggressive at invading tissue and detaching vaginal cells, making the infection harder to clear completely.
Non-albicans species like Candida glabrata also play a role in recurrent cases. These species are more likely to resist standard antifungal treatments, which means a treatment that clears one infection may not work on the next. If you’ve treated a yeast infection with over-the-counter medication and symptoms keep returning, a different Candida species could be the reason.
Less Obvious Contributing Factors
Sexual activity doesn’t cause yeast infections in the way a sexually transmitted infection spreads, but it can contribute. Friction and the introduction of new bacteria during intercourse can shift the vaginal environment enough to trigger overgrowth in someone already predisposed. Spermicides and certain lubricants may also irritate tissue and alter pH.
Stress is another underappreciated factor. Chronic stress raises cortisol levels, which suppresses parts of the immune system responsible for keeping fungal populations in check. Combined with the sleep disruption and dietary changes that often accompany stressful periods, this creates conditions where Candida can gain a foothold. Many women notice a pattern of infections during particularly demanding stretches of their lives, and this connection is real, not coincidental.