Yeast infections happen when a fungus called Candida, which normally lives on your skin and inside your body in small amounts, grows out of control. This overgrowth is usually triggered by something that disrupts the body’s natural balance, whether that’s antibiotics, hormonal changes, excess moisture, or a weakened immune system. Around 138 million women worldwide deal with recurrent yeast infections every year, and most women will experience at least one in their lifetime. Men can get them too, though less commonly.
What Happens Inside Your Body
Candida is part of your normal flora. In the vagina, beneficial bacteria called lactobacilli act as a biological barrier. They compete with Candida for space on the vaginal lining and help maintain an acidic environment that keeps fungal growth in check. As long as this ecosystem stays balanced, Candida causes no problems.
When something disrupts that balance, Candida shifts from a harmless yeast form into a more aggressive form that can penetrate tissue and trigger inflammation. This transition is what turns a quiet, coexisting organism into an active infection with itching, burning, and discharge. The disruption can come from inside your body (like immune changes or blood sugar spikes) or from outside factors (like medications or moisture).
Antibiotics Are the Most Common Trigger
Antibiotics kill bacteria, and they don’t distinguish between harmful bacteria and the protective lactobacilli in your vagina. When those beneficial bacteria are wiped out, Candida has fewer competitors and more room to multiply. This is why yeast infections so often follow a course of antibiotics for something completely unrelated, like a sinus infection or urinary tract infection. The longer you take antibiotics, the higher the risk.
Hormonal Shifts and Pregnancy
Estrogen plays a direct role in how hospitable your body is to Candida. Higher estrogen levels increase the glycogen (a type of sugar) stored in vaginal cells, which feeds the fungus. This is why yeast infections are more common during pregnancy, in the days before your period, and when taking hormonal birth control with higher estrogen doses. Women in their reproductive years are far more likely to get yeast infections than those who haven’t started menstruating or those who have gone through menopause.
Blood Sugar and Diabetes
Chronically high blood sugar creates ideal conditions for Candida. Elevated glucose in the blood means elevated glucose in vaginal secretions and skin surfaces, essentially giving the fungus a steady food supply. High blood sugar also weakens immune function and disrupts the vaginal microbiome, compounding the problem. People with poorly controlled diabetes are significantly more prone to yeast infections, and recurrent infections can sometimes be the first sign that blood sugar isn’t well managed. Certain diabetes medications that work by flushing excess sugar through the urinary tract can also raise the risk of genital yeast infections as a side effect.
Moisture, Clothing, and Heat
Candida thrives in warm, moist environments. Anything that traps heat and moisture against your skin creates favorable conditions for overgrowth. Wearing underwear made from synthetic fabrics, sitting in a wet swimsuit for hours, or spending long stretches in tight, non-breathable clothing can all contribute. Cotton underwear, or at least underwear with a cotton lining, allows air circulation and wicks moisture away from the skin. Changing out of sweaty workout clothes or wet swimwear promptly makes a real difference, especially in hot weather.
Douching and Scented Products
The vagina is self-cleaning. Douching, which involves flushing the vaginal canal with water or a mixture of fluids, disrupts the natural balance of bacteria and acidity that keeps infections at bay. The Office on Women’s Health states directly that douching can cause an overgrowth of harmful organisms, leading to yeast infections or bacterial vaginosis.
Scented tampons, pads, powders, sprays, and bubble baths can cause similar disruption. These products introduce chemicals that irritate vaginal tissue and alter its pH, making it easier for Candida to gain a foothold. Washing the external genital area with plain water or a mild, unscented soap is all that’s needed.
Sex Can Play a Role
Yeast infections are not classified as sexually transmitted infections because people who have never had sex get them regularly. That said, sexual activity does increase the risk. There’s a higher likelihood of vaginal yeast infections when you first become sexually active, and you can develop one after having sex with a partner who has a yeast infection. Oral-genital contact has also been linked to vaginal yeast infections. If you or a partner keeps getting reinfected, it’s worth considering whether the fungus is being passed back and forth.
Weakened Immune System
Your immune system is the other major line of defense against Candida overgrowth. When immune function is compromised, whether from HIV, chemotherapy, organ transplant medications, chronic stress, or sleep deprivation, the body becomes less effective at keeping fungal populations in check. Even temporary dips in immune function during illness or periods of intense physical stress can open the door to an infection.
How Men Get Yeast Infections
Men develop yeast infections most often on the head of the penis, a condition called balanitis. The Candida fungus lives on moist skin, and when it overgrows, it causes redness, irritation, and sometimes a white, patchy coating. Men who are uncircumcised have a higher risk because the foreskin creates a warm, moist environment where Candida can flourish. Other risk factors for men include long-term antibiotic use, diabetes, a weakened immune system, being overweight, and poor hygiene. Having sex with a partner who has a vaginal yeast infection also raises the risk.
When Infections Keep Coming Back
If you’re getting three or more yeast infections in a single year, that’s considered recurrent. This affects fewer than 5% of women, but the impact on quality of life is significant. Recurrent infections aren’t always caused by something you’re doing wrong. Some people are simply more genetically susceptible to Candida overgrowth, or they carry a species of Candida that’s harder to clear. In these cases, the standard short-course treatment often isn’t enough, and a longer management plan is typically needed. If your infections keep returning, it’s also worth having your blood sugar checked, since recurrent yeast infections can be an early indicator of prediabetes or diabetes that hasn’t been diagnosed yet.