Yeast infections happen when a fungus called Candida, which normally lives in small amounts on your skin and inside your body, grows out of control. About 75% of all women will have at least one vaginal yeast infection in their lifetime, and up to 45% will have two or more. But yeast infections aren’t exclusive to women, and understanding what triggers that overgrowth can help you avoid repeat episodes.
What Happens Inside Your Body
Candida lives on your skin and mucous membranes all the time, usually without causing problems. In the vagina, beneficial bacteria (primarily Lactobacillus species) produce lactic acid that keeps the environment acidic, with a pH below 4.5. That acidity does two important things: it limits how much Candida can grow, and it prevents the fungus from shifting into a more aggressive form.
When something disrupts that acidic environment, Candida transforms. The fungus shifts from a round, passive yeast shape into long, branching filaments called hyphae. These filaments can physically push into the cells lining the vaginal wall and release a toxin called candidalysin that damages tissue and triggers inflammation. That inflammation is what produces the hallmark symptoms: itching, burning, swelling, and thick white discharge. If the overgrowth continues, Candida can form a layered structure called a biofilm that continuously releases new fungal cells, making the infection harder to clear and potentially leading to chronic or recurring episodes.
Antibiotics Are a Common Trigger
Taking antibiotics is one of the most frequent causes of yeast infections. Antibiotics kill bacteria, and they don’t distinguish between harmful bacteria and the protective Lactobacillus in your vagina or gut. When those beneficial bacteria are wiped out, the acidic environment they maintain collapses, and Candida seizes the opportunity to multiply. Broad-spectrum antibiotics (the kind prescribed for ear infections, sinus infections, or urinary tract infections) carry the highest risk because they affect the widest range of bacteria.
Making things worse, Candida can actually block Lactobacillus from recolonizing after a course of antibiotics. This means the window of vulnerability can last longer than the antibiotic course itself. If you’ve noticed a pattern of yeast infections following antibiotics, that connection is well established and worth mentioning to your prescriber.
Hormonal Changes
Estrogen plays a direct role in how hospitable the vaginal environment is for Candida. Higher estrogen levels increase the amount of glycogen (a sugar that feeds both Lactobacillus and yeast) stored in vaginal tissue. Situations that raise estrogen include pregnancy, hormone replacement therapy, and some birth control pills. Pregnancy is a particularly common trigger because estrogen levels climb steadily throughout all three trimesters, creating conditions where Candida thrives even when Lactobacillus is still present.
Hormonal shifts during the menstrual cycle also explain why some women notice symptoms flaring just before their period, when estrogen and progesterone levels change rapidly.
High Blood Sugar Feeds Yeast
People with uncontrolled diabetes face a significantly higher risk. When blood sugar is elevated, excess sugar can be released through urine and vaginal secretions, essentially feeding Candida directly. The CDC specifically notes this connection for women with diabetes. The risk drops substantially when blood sugar is well managed, which is one reason doctors check for diabetes in people with recurring yeast infections that don’t respond to standard treatment.
A Weakened Immune System
Your immune system normally keeps Candida populations in check. Anything that suppresses immune function opens the door to overgrowth. This includes HIV/AIDS, chemotherapy, organ transplant medications, and long-term use of corticosteroids (like prednisone). People receiving these treatments are at higher risk for yeast infections not just vaginally but in the mouth (oral thrush), throat, and even the bloodstream in severe cases.
Stress and sleep deprivation also dampen immune responses, though their contribution is harder to quantify than the effect of immunosuppressive medications.
Products That Disrupt Vaginal pH
Douching is one of the clearest lifestyle risk factors. The vagina is self-cleaning, and flushing it with water or commercial douching solutions strips away the protective bacteria and alters the natural acidity. The Office on Women’s Health states directly that douching can cause an overgrowth of harmful bacteria and lead to yeast infections.
Other products that can disrupt the vaginal environment include scented tampons, scented pads, vaginal deodorant sprays, and perfumed soaps. Even bubble baths and certain laundry detergents can be irritating. The safest approach is washing the external genital area with warm water, or at most a mild, unscented soap, and avoiding putting any product inside the vagina.
Clothing and Moisture
Candida thrives in warm, moist environments. Tight-fitting clothing, synthetic underwear, wet swimsuits, and sweaty workout gear create exactly those conditions. Cotton underwear allows airflow and wicks moisture, which helps keep the skin dry. Changing out of wet or sweaty clothing promptly reduces the time Candida has to grow in ideal conditions.
Sexual Activity and Transmission
Yeast infections are not classified as sexually transmitted infections because you can absolutely get one without any sexual contact. However, sexual activity does play a role. You can get a yeast infection from a sexual partner, and you can pass one on through vaginal, oral, or anal sex. Condoms and dental dams reduce that risk.
If your partner is male, his risk of developing symptoms from exposure is relatively low. About 15% of men develop an itchy rash on the penis after unprotected sex with a partner who has a vaginal yeast infection. Whether a male partner needs treatment at the same time is something to consider if infections keep coming back.
Men Get Yeast Infections Too
Yeast infections in men typically appear as balanitis, a condition where the head of the penis becomes swollen, red, or itchy. Signs include moist skin on the penis, a thick white substance collecting in skin folds, shiny white patches, and a burning sensation. Men who are uncircumcised have a higher risk because the foreskin creates a warm, moist space where Candida grows easily.
Other risk factors for men are the same as for women: long-term antibiotic use, diabetes, a weakened immune system, being overweight, and poor hygiene. The fungus is often already present on the skin, and it only becomes a problem when conditions shift in its favor.
Recurrent Yeast Infections
If you’re getting three or more yeast infections in a single year, that’s classified as recurrent vulvovaginal candidiasis. It affects fewer than 5% of women, but it carries a real quality-of-life burden. Recurrent infections sometimes involve a different species of Candida that’s harder to treat with standard antifungal medications, or they point to an underlying issue like undiagnosed diabetes or immune suppression. A healthcare provider can test to identify the specific type of yeast involved and adjust treatment accordingly.
People with recurrent infections often benefit from longer courses of antifungal treatment or a maintenance regimen designed to keep Candida suppressed over several months. Addressing underlying triggers, whether that’s switching birth control, managing blood sugar, or eliminating irritating products, is just as important as treating the infection itself.