Yeast infections happen when a fungus called Candida, which already lives on your skin and in your body, grows out of control. Up to 75% of women will experience at least one vaginal yeast infection in their lifetime, making it one of the most common infections there is. The fungus isn’t something you “catch” from the outside. It’s already present in small amounts, kept in check by the bacteria that naturally live alongside it. When something disrupts that balance, yeast multiplies fast.
The Balance That Keeps Yeast in Check
Your body hosts a community of bacteria and fungi that coexist in a careful equilibrium. In the vagina, beneficial bacteria (especially a group called Lactobacilli) maintain an acidic environment that prevents yeast from taking over. As long as these protective bacteria are thriving, Candida stays at low, harmless levels.
When something knocks that bacterial population down or changes the local environment, Candida seizes the opportunity. It shifts from a passive, rounded form into an aggressive one that can dig into tissue and trigger the itching, burning, and discharge that characterize a yeast infection. The triggers that tip this balance fall into several categories, and most people encounter at least one of them regularly.
Antibiotics Are the Most Common Trigger
Antibiotics kill bacteria. That’s the point. But they don’t distinguish between harmful bacteria causing your sinus infection and the beneficial bacteria keeping yeast under control in your vagina or on your skin. A course of antibiotics can wipe out enough protective Lactobacilli to leave yeast essentially unopposed. This is why yeast infections so often show up a few days into or just after finishing an antibiotic prescription.
Broad-spectrum antibiotics, the kind prescribed for a wide range of infections, carry the highest risk because they eliminate the widest variety of bacteria. If you’ve noticed a pattern of getting yeast infections after taking antibiotics, you’re not imagining it. It’s one of the best-documented risk factors.
Hormones Play a Major Role
Estrogen directly affects how hospitable your body is to yeast. Higher estrogen levels increase the amount of glycogen (a sugar that yeast feeds on) in vaginal tissue, and estrogen also suppresses parts of the local immune response that would normally keep fungal growth in check. Research has shown that estrogen signaling actually influences gene expression in Candida, helping the fungus grow and become more virulent.
This explains why yeast infections are more common during pregnancy, when estrogen levels surge. It also explains the link to hormonal contraceptives, particularly higher-dose estrogen pills, and to hormone replacement therapy in postmenopausal women. Fluctuations during your menstrual cycle can play a role too. Many people notice yeast infections tend to appear in the days just before their period, when hormone shifts are at their peak.
High Blood Sugar Feeds the Fungus
Yeast thrives on sugar. When blood glucose levels run high, your body tries to clear the excess through urine and other secretions, which raises sugar levels in the genital area and creates ideal conditions for Candida to multiply. People with diabetes, particularly those with poorly controlled blood sugar, experience yeast infections at significantly higher rates. Even prediabetes can increase risk.
If you’re getting frequent yeast infections without an obvious trigger like antibiotics, it’s worth checking your blood sugar levels. Recurrent infections are sometimes the symptom that first points toward a blood sugar problem.
Moisture, Clothing, and Hygiene Habits
Candida grows best in warm, moist environments. Anything that traps heat and moisture against your skin creates a friendlier climate for yeast. Synthetic underwear is a common culprit. Cotton is breathable and wicks moisture away, while nylon, polyester, and similar fabrics hold sweat against the skin. Even underwear marketed as having a “cotton crotch panel” doesn’t fully protect you, because the surrounding synthetic material still limits airflow.
Sitting in a wet swimsuit or sweaty workout clothes for hours has the same effect. Panty liners worn daily (outside of your period) also reduce breathability and can contribute to irritation. Going without underwear at night, or wearing loose pajamas, increases airflow and can help if you’re prone to infections.
Douching is one of the most direct ways to disrupt the vaginal environment. A healthy vagina maintains its own acidity, and douching strips away both the protective bacteria and the acidic conditions they create. The U.S. Office on Women’s Health specifically warns that douching can cause yeast overgrowth. Scented tampons, pads, powders, and sprays carry similar risks by introducing chemicals that alter the vaginal flora.
Yeast Infections in Men
Men get yeast infections too, though less frequently. The infection typically affects the head of the penis (called balanitis) and causes redness, itching, and sometimes a white, patchy coating. Candida thrives in the warm, moist space under the foreskin, which is why uncircumcised men and children under four have the highest rates. A condition called phimosis, where the foreskin can’t be fully pulled back, further increases risk by trapping moisture.
Poor hygiene, harsh soaps, and not rinsing or drying thoroughly after bathing all contribute. Men can also develop yeast infections after sex with a partner who has one, though yeast infections are not classified as sexually transmitted infections because they originate from fungus already present on the body.
When Yeast Infections Keep Coming Back
Most yeast infections are isolated events that clear up with treatment. But some people deal with them repeatedly. Recurrent vulvovaginal candidiasis is defined as three or more episodes within a single year, and it affects fewer than 5% of women. Globally, though, that still translates to roughly 138 million women dealing with recurrent infections annually.
Recurrent infections often involve multiple overlapping risk factors: a genetic predisposition to weaker local immune responses, ongoing hormonal influences, chronic high blood sugar, or repeated antibiotic use. If your infections keep returning, the cause usually isn’t a single habit you can change but a combination of factors that need to be addressed together. Identifying the specific triggers in your case, whether hormonal, metabolic, or environmental, is the most effective path to breaking the cycle.