Yeast infections happen when a fungus called Candida, which normally lives in small amounts on your skin and mucous membranes, grows out of control. About three-quarters of women will experience at least one vaginal yeast infection in their lifetime, and roughly 10% of those will deal with recurrent infections. The fungus doesn’t come from nowhere. It’s already there, kept in check by your immune system and the balance of bacteria in your body, until something tips that balance.
What Happens Inside Your Body
Candida exists on your body in a harmless yeast form most of the time. Your vaginal lining, for instance, can tolerate small amounts of this yeast without triggering any symptoms. The problem starts when conditions change and the fungus shifts into an aggressive form, sprouting long filaments called hyphae that can physically invade tissue. This shape-shifting is one of Candida’s most effective survival tricks: the filaments resist your immune cells and can even disguise their surface markers so your immune system doesn’t recognize them as quickly.
When this transition happens on a large scale, the cells lining your vaginal wall can no longer tolerate the fungal load. They launch an intense inflammatory response, which is what produces the hallmark symptoms: itching, burning, swelling, and thick white discharge. The infection itself is essentially your body reacting to a fungus it previously coexisted with peacefully.
Antibiotics Are a Common Trigger
Taking antibiotics is one of the most well-known causes of yeast infections. Antibiotics kill bacteria, but they don’t distinguish between harmful bacteria and the protective bacteria (especially Lactobacillus species) that help keep Candida in check. When those protective populations drop, Candida has room to expand. Not all antibiotics carry the same risk. A study comparing acne medications found that azithromycin more than doubled the risk of a vaginal yeast infection afterward, while doxycycline raised the risk by about 24%. Broad-spectrum antibiotics that wipe out a wider range of bacteria tend to cause the most disruption.
Hormones and Blood Sugar
Estrogen plays a direct role in creating an environment where yeast can thrive. Higher estrogen levels cause vaginal cells to accumulate more glycogen, a stored sugar that can exceed free glucose levels in the vagina by roughly tenfold. This sugar-rich environment gives Candida more fuel. That’s why yeast infections are more common during pregnancy, in the days around ovulation, and in people taking hormonal contraceptives with higher estrogen doses.
Diabetes creates a similar problem through a different route. When blood sugar runs high, excess glucose can show up in urine and vaginal secretions, feeding yeast and bacteria. People with poorly controlled diabetes are significantly more prone to yeast infections, and managing blood sugar levels is often a key part of reducing recurrence.
Clothing, Moisture, and Everyday Habits
Yeast thrives in warm, moist environments. Synthetic fabrics like nylon and spandex trap heat and moisture against the skin, creating ideal conditions for overgrowth. Cotton underwear allows the area to breathe and helps reduce that risk. Beyond fabric choice, sitting in a wet swimsuit for hours, wearing tight leggings during long workouts, or using scented soaps and douches can all shift the vaginal environment in ways that favor Candida. The vagina is largely self-cleaning, and introducing harsh products disrupts its natural chemistry.
Weakened Immune Defenses
Your immune system is the main reason Candida stays in its harmless yeast form most of the time. A specific branch of immune cells, T cells, plays a central role in keeping the fungus suppressed. Anything that weakens T cell function can open the door to yeast overgrowth. HIV, chemotherapy, long-term corticosteroid use, and organ transplant medications all significantly raise the risk. Some people have inherited immune conditions that specifically impair their ability to fight Candida, leading to chronic infections of the mouth, skin, and genitals that keep returning despite treatment.
Can You Get It From a Partner?
Yeast infections are not classified as sexually transmitted infections, but they can be passed between partners during sex. About 15% of men develop symptoms of a penile yeast infection after intercourse with an infected female partner. Oral sex can also transmit yeast, potentially causing thrush (an oral yeast infection). A male partner with a yeast infection can pass it back to a female partner as well. That said, the vast majority of yeast infections arise from changes in your own body’s balance rather than from sexual contact.
How Men Get Yeast Infections
Men can develop yeast infections too, most commonly on the head of the penis. Being uncircumcised is the biggest risk factor: about 1 in 30 uncircumcised men will experience a penile yeast infection. The foreskin creates a warm, moist fold of skin where Candida thrives, especially if the area isn’t cleaned and dried thoroughly. Not rinsing soap completely from under the foreskin, using harsh cleansers, and poor overall hygiene all increase the risk. The same systemic factors that affect women, like diabetes, antibiotics, and immune suppression, also apply to men.
Why Some People Get Repeated Infections
Recurrent yeast infections, defined as four or more episodes per year, affect up to 9% of women who get them. Even with proper antifungal treatment followed by months of maintenance therapy, about half of women relapse once that treatment ends. Recurrence often points to an underlying factor that hasn’t been addressed: ongoing antibiotic use, uncontrolled blood sugar, a hormonal pattern, or a subtle immune issue. Some research suggests that certain probiotic strains, particularly Lactobacillus acidophilus and Lactobacillus rhamnosus taken alongside standard antifungal treatment, may help reduce recurrence when used during the premenstrual period each month. The evidence is still mixed, but the logic is straightforward: replenishing protective bacteria makes it harder for Candida to regain a foothold.
For people dealing with frequent infections, identifying and addressing the specific trigger is usually more effective than treating each episode individually. Keeping blood sugar stable, switching to a narrower-spectrum antibiotic when possible, choosing breathable fabrics, and avoiding products that disrupt vaginal pH all reduce the odds of another round.