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 women will get at least one vaginal yeast infection in their lifetime, and 40% to 45% will get two or more. While vaginal infections are the most common type, yeast infections can also affect men, the mouth, and skin folds. The triggers are surprisingly varied, ranging from antibiotics to tight clothing to hormonal shifts.
What Causes Candida to Overgrow
Candida is a normal part of your body’s microbiome. In the vagina, beneficial bacteria (primarily Lactobacillus) keep Candida populations in check by maintaining an acidic environment with a pH between 3.8 and 4.5. A yeast infection develops when something disrupts this balance, giving Candida the opportunity to multiply rapidly.
Once conditions shift in Candida’s favor, the fungus transitions from a harmless round shape into an elongated form that can penetrate tissue. It attaches to the cells lining the vaginal wall, forms protective clusters called biofilms, and releases enzymes that break down surrounding tissue. This is what produces the itching, burning, and thick discharge that characterize a yeast infection.
Antibiotics Are the Most Common Trigger
Taking antibiotics is one of the most frequent causes of yeast infections. Antibiotics kill bacteria indiscriminately, wiping out the protective Lactobacillus alongside whatever infection you’re treating. With those beneficial bacteria gone, Candida faces little competition and can multiply freely. This is why yeast infections often show up toward the end of an antibiotic course or shortly after finishing one.
Broad-spectrum antibiotics, the type prescribed for a wide range of bacterial infections, carry the highest risk because they affect the greatest variety of bacteria in your body.
How Hormones Play a Role
Estrogen directly influences your risk of yeast infections. Higher estrogen levels cause vaginal cells to store more glycogen, a form of sugar that Candida feeds on. Free glycogen in the vagina can exceed glucose levels by roughly tenfold during peak estrogen phases. This explains why yeast infections are more common during certain points in the menstrual cycle, particularly around ovulation when estrogen peaks.
Pregnancy dramatically raises estrogen levels, making yeast infections especially common during the second and third trimesters. Hormonal birth control that contains estrogen can have a similar effect, though the risk varies from person to person. On the other end of the spectrum, yeast infections are rare before puberty and less common after menopause, when estrogen levels are naturally lower.
Blood Sugar and Diabetes
Yeast feeds on sugar, so elevated blood sugar creates ideal growth conditions. If you have diabetes that isn’t well controlled, glucose levels in vaginal secretions and other body fluids rise along with your blood sugar. This gives Candida a rich food supply and is one reason people with unmanaged diabetes experience recurrent yeast infections. Getting blood sugar under tighter control often reduces the frequency of infections significantly.
Even without a diabetes diagnosis, diets very high in refined sugar may contribute to yeast overgrowth in some people, though the evidence for this is less clear-cut than for clinical hyperglycemia.
Clothing, Moisture, and Heat
Candida thrives in warm, dark, moist environments. Sitting in a wet bathing suit after swimming, staying in sweaty workout clothes, or wearing tight synthetic underwear all create exactly those conditions. The longer moisture stays trapped against your skin, the more opportunity yeast has to grow.
A few practical changes lower your risk considerably:
- Change out of wet clothes immediately after swimming or exercising
- Choose cotton underwear and loose-fitting bottoms, especially in warm weather
- Wear moisture-wicking fabrics during workouts to help sweat evaporate faster
- Avoid hot tubs and very hot baths, which create the warmth and humidity Candida loves
A Weakened Immune System
Your immune system normally keeps Candida populations small. Anything that suppresses immune function can tip the balance. This includes conditions like HIV, medications such as corticosteroids or chemotherapy, chronic stress, and severe sleep deprivation. People who are immunocompromised tend to get yeast infections more frequently and may find them harder to clear.
Yeast Infections in Men
Men get yeast infections too, though less commonly. The infection typically develops on the head of the penis, causing redness, itching, and sometimes a white, patchy discharge. Uncircumcised men face the highest risk because the foreskin creates a warm, moist environment where Candida can grow. About 1 in 30 uncircumcised men will develop a penile yeast infection.
Risk factors for men include poor hygiene, not rinsing soap off the foreskin completely, not drying off thoroughly, and having a tight foreskin that can’t be pulled back easily. Diabetes and immunosuppression raise the risk in men just as they do in women.
Can You Get One From a Partner?
A yeast infection is not classified as a sexually transmitted infection because you can develop one without any sexual contact. That said, transmission between partners is possible. If a male partner has unprotected sex with someone who has an active yeast infection, there’s about a 15% chance he’ll develop an itchy rash on the penis. A female partner is at higher risk and should watch for symptoms. Condoms and dental dams reduce the chance of passing the infection during vaginal, oral, or anal sex.
Other Contributing Factors
Douching and scented vaginal products disrupt the natural bacterial balance and can set the stage for yeast overgrowth. The vagina is self-cleaning, and introducing soaps, sprays, or douches inside it does more harm than good. Spermicides may also irritate vaginal tissue and shift the microbial environment in Candida’s favor.
Stress deserves mention as well. Chronic stress raises cortisol levels, which suppresses parts of the immune response that normally keep fungal growth in check. Many people notice a pattern of yeast infections during particularly stressful periods, and the biology supports the connection.