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. Most of the time, your immune system and the balance of bacteria in your body keep Candida in check. When something disrupts that balance, the fungus multiplies rapidly and causes symptoms like itching, burning, and discharge.
About 75% of women will experience at least one vaginal yeast infection in their lifetime, but yeast infections can also affect men, the mouth, throat, and other parts of the body. Understanding what tips the balance helps you recognize why they happen and what you can do to lower your risk.
The Role of Your Body’s Natural Balance
Your body hosts Candida as a normal resident. In the vagina, beneficial bacteria (primarily Lactobacillus species) produce lactic acid that keeps the environment slightly acidic, with a healthy pH below 4.5. This acidity suppresses Candida growth and prevents it from shifting into its more aggressive form. When something reduces these protective bacteria or changes the local environment, Candida seizes the opportunity.
The exact biological trigger that flips Candida from a harmless passenger to a problem-causer isn’t fully understood. What researchers do know is that the fungus can change its behavior, growing thread-like structures that penetrate tissue and provoke inflammation. Several well-established factors make this transition more likely.
Antibiotics Are a Leading Trigger
Antibiotics kill bacteria, but they don’t discriminate. A course of broad-spectrum antibiotics wipes out harmful bacteria along with the protective ones that keep Candida in check. Research published in the American Journal of Obstetrics & Gynecology found that women who used antibiotics in the month before developing a yeast infection were about 75% more likely to have one compared to women who hadn’t taken antibiotics. Nearly one in five women with a Candida infection had used antibiotics recently, compared to roughly one in eight in the control group.
This doesn’t mean you should avoid antibiotics when you need them. It does explain why yeast infections so often follow treatment for a sinus infection, UTI, or strep throat.
Hormones and Blood Sugar
Estrogen plays a significant role. Higher estrogen levels increase the amount of glycogen (a sugar the body stores) in vaginal tissue, and Candida feeds on sugar. This is why yeast infections are more common during pregnancy, when estrogen surges, and why some women notice them more frequently while taking certain hormonal contraceptives.
Diabetes creates a similar problem through a different path. When blood sugar runs high, excess sugar can end up in vaginal secretions and urine, creating an environment where yeast thrives. The CDC lists diabetes as a standalone risk factor for vaginal yeast infections, oral thrush, and even more serious internal Candida infections. Women with diabetes who struggle to manage their blood sugar are particularly vulnerable.
Immune System Suppression
Your immune system is the primary force holding Candida in check, so anything that weakens it raises your risk. The CDC identifies several conditions and treatments that increase susceptibility to yeast infections:
- HIV/AIDS, which impairs the immune cells that normally fight fungal infections
- Cancer and chemotherapy, which suppress the immune system broadly
- Corticosteroids, including inhaled steroids used for asthma, which can cause oral thrush when the medication deposits in the mouth and throat
People with severely weakened immune systems face not only surface-level yeast infections but also the risk of invasive candidiasis, where the fungus enters the bloodstream. This is a much more serious condition, but it primarily affects hospitalized or critically ill patients.
Clothing, Moisture, and Everyday Habits
Candida thrives in warm, moist environments. Anything that traps heat and moisture against your skin creates conditions the fungus loves. The Cleveland Clinic recommends cotton underwear specifically because it wicks away sweat and moisture that yeast feed on. Synthetic fabrics hold moisture against the skin. Even underwear labeled with a “cotton crotch panel” doesn’t offer the same breathability as fully cotton fabric.
Other everyday factors that create a yeast-friendly environment include sitting in a wet swimsuit for extended periods, wearing very tight pants or leggings regularly, and using scented soaps, douches, or sprays in the genital area. These products can disrupt the natural bacterial balance, opening the door for Candida overgrowth. The vagina is self-cleaning, and adding products to it tends to cause more problems than it solves.
Can You Get a Yeast Infection From Sex?
Yeast infections aren’t classified as sexually transmitted infections, but sex can play a role. According to the Mayo Clinic, your risk of developing a yeast infection increases if you have sex with a partner who currently has one. The friction of intercourse can also cause small irritations that make tissue more vulnerable to fungal overgrowth.
Men can get yeast infections too, typically as balanitis, an infection of the head of the penis. Risk factors for men include being uncircumcised, having diabetes, long-term antibiotic use, being overweight, and poor hygiene. The Candida fungus naturally lives on moist skin, and when conditions favor its growth, men can develop redness, itching, and irritation just as women do.
Yeast Infections Beyond the Vagina
While vaginal yeast infections get the most attention, Candida can cause problems in several areas. Oral thrush appears as white patches on the tongue, inner cheeks, and throat. It’s more common in people using inhaled corticosteroids, those with diabetes, and people living with HIV/AIDS. Rinsing your mouth after using an inhaler significantly reduces this risk.
Esophageal candidiasis, a yeast infection in the tube connecting the throat to the stomach, is one of the most common infections in people with HIV/AIDS. Skin yeast infections tend to develop in warm folds, under breasts, in the groin, and between fingers, particularly in people who are overweight or who sweat heavily.
When Yeast Infections Keep Coming Back
Most people get an occasional yeast infection that clears up with treatment. But for a smaller group, fewer than 5% of women, the infections recur three or more times within a single year. This is classified as recurrent vulvovaginal candidiasis, and it requires a different management approach than a one-time infection.
Recurrent infections sometimes signal an underlying issue worth investigating: undiagnosed diabetes, an immune deficiency, or a non-albicans Candida species that doesn’t respond to standard treatments. If you’re dealing with frequent yeast infections, identifying and addressing the root cause matters more than repeatedly treating symptoms. Some people also find that certain patterns in their life, like antibiotic use for a chronic condition or hormonal fluctuations tied to their cycle, correlate closely with their episodes.