Yeast infections happen when a fungus called Candida, which normally lives on your skin and mucous membranes without causing problems, grows out of control. An estimated 75% of women will have at least one vaginal yeast infection in their lifetime, and 40% to 45% will have two or more. But yeast infections aren’t limited to the vagina. They can develop in the mouth, on the penis, in skin folds, and anywhere else warm, moist conditions let Candida thrive.
Why Yeast Grows Out of Control
Candida lives on most people’s bodies as a harmless resident. Your immune system and the other microbes sharing that space keep it in check. Problems start when one of three things breaks down: the local community of bacteria gets disrupted, the tissue barrier weakens, or the immune system can’t do its job properly.
When conditions shift in Candida’s favor, the fungus changes form. It transitions from a round yeast shape into elongated filaments that can physically invade tissue. In this invasive form, it produces a toxin called candidalysin that damages cells and triggers inflammation. That’s when you start feeling symptoms like itching, burning, and discharge. The fungus hasn’t appeared out of nowhere. It was already there, waiting for the balance to tip.
Antibiotics Are the Most Common Trigger
Taking antibiotics is one of the fastest ways to develop a yeast infection. Antibiotics kill bacteria, and that includes the beneficial bacteria that normally compete with Candida for space and resources. In the vagina, species of Lactobacillus maintain an acidic environment that keeps yeast populations small. When antibiotics wipe out these bacteria, the pH shifts, Candida faces less competition, and overgrowth follows. This is why yeast infections so often show up during or just after a course of antibiotics for something completely unrelated, like a sinus infection or urinary tract infection.
Hormones and Estrogen
Estrogen plays a direct role in creating conditions that favor yeast. Higher estrogen levels cause the vaginal lining to accumulate more glycogen, a sugar that Candida feeds on. Free glycogen in the vagina can exceed glucose levels by roughly tenfold. This is why yeast infections are more common during pregnancy, when estrogen surges dramatically, and in people using estrogen-containing birth control or hormone replacement therapy.
The menstrual cycle matters too. Yeast infections are more likely around the ovulatory phase, when estrogen peaks and glycogen stores are at their highest. Before puberty and after menopause, when estrogen levels are low, vaginal yeast infections are much less common.
Blood Sugar and Diabetes
Yeast thrives in high-sugar conditions. People with diabetes, particularly those with poorly controlled blood sugar, face a significantly higher risk of yeast infections in multiple areas of the body, including the vagina, mouth, and skin folds. Elevated blood glucose gives Candida more fuel to grow, but that’s not the only mechanism at work. Diabetes also alters immune signaling, shifts the balance of the normal microbiome in the mouth and vagina, and often leads to more frequent use of antibiotics and steroids, all of which independently raise yeast infection risk.
If you’re getting frequent yeast infections and haven’t been screened for diabetes or prediabetes, it’s worth investigating. Recurring infections can sometimes be an early sign that blood sugar isn’t well regulated.
Hygiene Products That Backfire
The vagina is self-cleaning and maintains its own acidic pH to ward off infections. Douching disrupts this system by washing away the protective bacteria and altering the natural acidity, which can cause an overgrowth of harmful organisms including Candida. Scented tampons, pads, powders, and sprays can also increase your chances of developing a vaginal infection. Even mild soaps can cause dryness and irritation if you have sensitive skin or an existing infection.
The simplest approach is to wash the external genital area with warm water, or at most a very gentle, unscented cleanser. Nothing needs to go inside the vaginal canal.
Clothing and Moisture
Candida grows best in warm, moist environments. Cotton underwear is the best choice because it’s breathable and wicks away excess sweat and moisture. Synthetic fabrics trap heat and dampness against the skin, creating conditions that favor yeast. Even underwear made from synthetic material with a small cotton crotch panel doesn’t fully protect you, since the surrounding synthetic fabric still limits airflow.
Sitting in a wet swimsuit or sweaty workout clothes for hours creates the same problem. Changing into dry clothes promptly after swimming or exercising reduces the window of time yeast has to multiply.
Sexual Activity
Yeast infections are not considered sexually transmitted infections because you can get one without having sex. But sexual contact can play a role. You can get a yeast infection from a partner during vaginal, oral, or anal sex. If a male partner has unprotected sex with someone who has a vaginal yeast infection, about 15% of men will develop an itchy rash on the penis. Female partners are more likely to pick up the infection and should get tested if symptoms appear.
Sex can also contribute to yeast infections indirectly. Friction and irritation can compromise the tissue barrier, lubricants and spermicides can alter vaginal pH, and saliva introduced during oral sex can disrupt the local microbial balance.
How Men Get Yeast Infections
Men develop yeast infections most often on the head of the penis, a condition called balanitis. The same Candida fungus is responsible. Being uncircumcised is the biggest anatomical risk factor, because the foreskin creates a warm, moist fold where yeast can accumulate. Other risk factors mirror those for vaginal yeast infections: long-term antibiotic use, diabetes, a weakened immune system, being overweight, and poor hygiene. Sex with a partner who has a vaginal yeast infection also increases the risk.
Weakened Immune System
Anything that compromises immune function gives Candida an opening. This includes HIV, chemotherapy, organ transplant medications, and long-term use of corticosteroids (oral or inhaled). People using inhaled steroids for asthma, for example, are more prone to oral yeast infections, commonly known as thrush. Rinsing the mouth after using an inhaler helps reduce this risk.
Chronic stress and sleep deprivation can also weaken immune surveillance enough to let yeast gain a foothold, though these factors are harder to quantify than medication effects.
Recurrent Yeast Infections
Some people deal with yeast infections over and over. The medical threshold for “recurrent” is typically three or more episodes in a single year. At that point, the pattern usually signals an underlying factor that hasn’t been addressed: uncontrolled blood sugar, ongoing antibiotic use, a hormonal shift, or sometimes a strain of Candida that doesn’t respond well to standard treatments. About 5% to 8% of women with vaginal yeast infections fall into this recurrent category, and they often need a different treatment approach than someone dealing with a one-time episode.
If your yeast infections keep coming back, tracking potential triggers like antibiotic courses, menstrual cycle timing, or new products can help identify what’s driving the pattern.