About 75% of women will get at least one vaginal yeast infection in their lifetime, and 40% to 45% will get two or more. The reason comes down to a delicate ecosystem inside the vagina that can tip out of balance surprisingly easily. Yeast (most commonly a fungus called Candida albicans) lives naturally in the vaginal tract in small amounts. It only becomes an infection when something disrupts the conditions that normally keep it in check.
How the Vaginal Ecosystem Keeps Yeast Under Control
A healthy vagina maintains a slightly acidic environment, largely thanks to beneficial bacteria called Lactobacillus. These bacteria feed on glycogen (a form of sugar stored in the cells lining the vaginal walls) and produce lactic acid as a byproduct. That lactic acid keeps the pH low enough to suppress yeast growth. When this system works well, Candida stays at harmless levels.
Not all Lactobacillus species are equally effective at this job. One strain, Lactobacillus crispatus, produces significantly more lactic acid than another common strain called Lactobacillus iners, giving it a stronger ability to inhibit Candida growth. Women whose vaginal microbiome is dominated by L. crispatus tend to have better protection against yeast colonization. The balance between these bacterial populations matters, and it varies from person to person.
The immune system also plays a role locally. Specialized immune cells in the vaginal lining produce signaling molecules that help clear Candida when it starts to multiply. When this immune response is weakened or misdirected, it can allow yeast to transition from a harmless resident to an active infection, sometimes triggering inflammation that makes symptoms worse.
Hormones Are a Major Driver
Estrogen and progesterone directly influence yeast infection risk because they control how much glycogen is stored in vaginal tissue. Higher estrogen levels mean more glycogen, which feeds Lactobacillus and supports the acidic environment that keeps yeast suppressed. This is why yeast infections are most common during reproductive years, when estrogen is at its peak.
But this relationship cuts both ways. Hormonal fluctuations during the menstrual cycle, pregnancy, or from hormonal birth control can temporarily shift the balance. Pregnancy raises estrogen dramatically, which is one reason yeast infections are more frequent during pregnancy. Hormonal contraceptives, particularly higher-dose options, can have a similar effect by altering the vaginal environment.
During menopause, estrogen drops significantly. The cells lining the vagina lose glycogen, and without enough glycogen to feed on, Lactobacillus populations decline. This makes the vaginal environment more vulnerable to overgrowth by yeast and other organisms. It seems counterintuitive that both high and low estrogen states can increase risk, but they do so through different mechanisms: high estrogen can create excess sugar that feeds yeast directly, while low estrogen removes the food source for the protective bacteria.
Antibiotics Wipe Out Protective Bacteria
Antibiotics are one of the most common triggers for yeast infections. They kill bacteria broadly, not selectively, which means a course of antibiotics for a sinus infection or urinary tract infection can devastate the Lactobacillus population in the vagina at the same time. With those protective bacteria gone, the acidic environment weakens and Candida can multiply rapidly. This is why many women develop a yeast infection shortly after finishing antibiotics.
Blood Sugar and Diabetes
Women with diabetes, particularly when blood sugar is poorly controlled, face a higher risk of yeast infections. The mechanism is straightforward: when blood sugar runs high, excess sugar can appear in vaginal secretions and urine, creating a richer food supply for yeast. Candida thrives on sugar, so chronically elevated glucose essentially fertilizes the fungus. Managing blood sugar levels effectively reduces this risk.
Habits That Shift the Balance
Several everyday habits can disrupt the vaginal microbiome enough to trigger an infection. Douching is one of the most well-documented. It washes away beneficial bacteria and alters the natural acidity of the vagina, which can lead directly to yeast overgrowth. Women who douche weekly are five times more likely to develop bacterial imbalances than women who don’t, and yeast infections follow the same pattern.
Scented tampons, pads, powders, and sprays also increase infection risk by introducing chemicals that irritate vaginal tissue and disturb the microbial balance. The vagina is self-cleaning, and these products work against that natural process rather than supporting it.
Wearing tight, non-breathable clothing or staying in wet swimwear creates a warm, moist environment where yeast multiplies more easily. Cotton underwear and changing out of damp clothing promptly are simple ways to reduce this risk.
Weakened Immunity
Anything that suppresses your immune system can increase vulnerability to yeast infections. This includes conditions like HIV, medications such as corticosteroids, chemotherapy, and even prolonged stress or sleep deprivation. The vaginal immune response depends on specialized cells that actively monitor and suppress Candida. When that surveillance weakens, yeast that was previously kept at low levels can grow unchecked.
Why Some Women Get Repeated Infections
For some women, yeast infections become a recurring problem, defined as four or more episodes in a single year. This can happen for several overlapping reasons. Some women naturally have a vaginal microbiome that’s less effective at suppressing Candida, particularly if their Lactobacillus population is dominated by less protective strains. Genetic differences in the local immune response also play a role. In some cases, an overactive inflammatory response in the vaginal lining actually worsens symptoms and creates conditions that allow reinfection.
Recurrent infections can also involve non-albicans species of Candida, such as Candida glabrata, which are harder to treat with standard antifungal medications. If over-the-counter treatments keep failing, a different species may be responsible, and a lab culture can help identify it.
What Yeast Infections Feel Like
The classic symptoms are intense itching and irritation of the vulva and vaginal opening, along with a thick, white discharge often described as resembling cottage cheese. Burning during urination or intercourse is also common. The skin around the vulva may appear red and swollen. Symptoms can range from mildly annoying to severe enough to disrupt daily life.
These symptoms overlap with other conditions, including bacterial vaginosis and some sexually transmitted infections. If you’ve never had a yeast infection before, or if your symptoms don’t improve with treatment, getting a proper diagnosis matters. About two-thirds of women who self-diagnose a yeast infection actually have something else.
Reducing Your Risk
You can’t eliminate the possibility of yeast infections entirely, but several strategies lower the odds. Avoiding douching and scented products protects your vaginal microbiome. Wearing breathable fabrics and changing out of wet clothing helps keep the environment less hospitable to yeast. If you’re on antibiotics, being aware that a yeast infection may follow lets you respond quickly. For women with diabetes, keeping blood sugar within target range is one of the most effective preventive measures.
Probiotics containing Lactobacillus strains are widely marketed for vaginal health, but the evidence supporting them is mixed. Some studies suggest benefit, particularly from L. crispatus, while others show no significant effect. They’re unlikely to cause harm, but they’re not a guaranteed solution either.