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. Up to 75% of women will experience at least one vaginal yeast infection in their lifetime, making it one of the most common infections. The triggers are surprisingly ordinary: antibiotics, hormonal shifts, clothing choices, and even the soap you use can tip the balance.
What Actually Happens in Your Body
Candida lives in your vagina all the time, and that’s perfectly normal. A healthy vaginal environment keeps it in check through two main defenses: beneficial bacteria (primarily Lactobacillus) and a naturally acidic pH. The Lactobacillus bacteria produce lactic acid, which maintains that acidity and prevents Candida from switching into its aggressive form.
When something disrupts this balance, Candida transforms. It shifts from a round, passive yeast shape into long, branching filaments that can physically push into the cells lining your vaginal walls. In this invasive form, the fungus releases a toxin called candidalysin that damages tissue and triggers the inflammation responsible for the itching, burning, and discharge you feel. The low pH of a healthy vagina actually blocks this shape-shifting process, which is why anything that raises your vaginal pH or kills off protective bacteria can open the door to infection.
Antibiotics Are the Most Common Trigger
Broad-spectrum antibiotics are designed to kill a wide range of bacteria, but they can’t distinguish between harmful bacteria and the beneficial Lactobacillus in your vagina. When those protective bacteria are wiped out, the acidic environment weakens, and Candida has room to multiply unchecked. This is why yeast infections frequently show up during or shortly after a course of antibiotics for something completely unrelated, like a sinus infection or urinary tract infection.
Hormonal Changes That Raise Your Risk
Estrogen plays a direct role in yeast infection susceptibility. Higher estrogen levels increase the amount of glycogen (a sugar stored in cells) in the vaginal lining, which feeds Candida and can promote its shift into the invasive filament form. This is why yeast infections are more common at certain points in life:
- Pregnancy: The surge in estrogen during pregnancy creates a favorable environment for Candida. About 20% of pregnant women develop a vaginal yeast infection, and that number climbs to roughly 30% in the third trimester.
- Hormonal contraceptives: Birth control methods that contain estrogen can raise your baseline risk.
- Menstrual cycle fluctuations: Some women notice infections tend to appear at the same point in their cycle, typically when estrogen peaks.
High Blood Sugar Fuels Yeast Growth
Women with diabetes face a higher risk of yeast infections, particularly when blood sugar is poorly controlled. When glucose levels run high, excess sugar can end up in vaginal secretions and urine, essentially providing an all-you-can-eat buffet for Candida. This doesn’t apply only to people with a diabetes diagnosis. Anyone experiencing frequent blood sugar spikes, whether from undiagnosed diabetes or prediabetes, may notice more frequent infections.
Products That Disrupt Your Vaginal Environment
Your vagina is self-cleaning, and many of the products marketed for “feminine hygiene” actively work against it. Douching is one of the biggest offenders. It flushes out the protective bacteria and disrupts the natural acidity that keeps Candida in check, directly leading to overgrowth. Scented tampons, pads, powders, and sprays carry the same risk. They introduce chemicals that can irritate the vaginal lining and alter its microbial balance.
The simplest approach is also the safest: wash the external area with warm water and, if needed, a mild unscented soap. Skip everything else.
Clothing and Moisture
Candida thrives in warm, moist environments. Tight-fitting pants, leggings, and synthetic underwear trap heat and moisture against your skin, creating ideal conditions for fungal growth. Cotton underwear is the best choice because it wicks away sweat and moisture that yeast feeds on. Underwear made from synthetic fabrics with just a small cotton crotch panel doesn’t offer the same protection, since the surrounding synthetic material still traps moisture.
Sitting in a wet bathing suit or sweaty workout clothes for extended periods has the same effect. Changing into dry clothes promptly makes a real difference, especially in warm weather.
Can You Get a Yeast Infection From Sex?
A yeast infection is not considered a sexually transmitted infection because you can develop one without any sexual contact at all. That said, you can get a yeast infection from a sexual partner. About 15% of men develop an itchy rash on the penis after unprotected sex with a woman who has an active yeast infection. Condoms and dental dams reduce the risk of passing the infection through vaginal, oral, or anal sex.
If your partner is a woman, she may also be at risk and should be tested if she develops symptoms. For male partners, the risk is lower overall but increases for men who are uncircumcised, use antibiotics long-term, have diabetes, or have a weakened immune system.
Men Get Yeast Infections Too
Penile yeast infections (balanitis) happen through the same basic mechanism. Candida is already present on the skin, and certain conditions let it overgrow. The head of the penis becomes red, swollen, and itchy, sometimes with white patches or discharge. Risk factors for men include being uncircumcised (the warm, moist environment under the foreskin favors fungal growth), long-term antibiotic use, diabetes, a weakened immune system, and being overweight. Poor hygiene also contributes, since Candida accumulates in skin folds that aren’t kept clean and dry.
Other Factors That Lower Your Defenses
Anything that weakens your immune system gives Candida an advantage. This includes conditions like HIV, cancer treatment, and long-term use of corticosteroids. Even high stress and sleep deprivation can suppress immune function enough to make you more vulnerable, though these are harder to measure precisely.
The type of bacteria that naturally dominate your vaginal environment also matters. Some women have a vaginal microbiome dominated by a less protective species of Lactobacillus, which produces a more inflammatory environment and actually encourages Candida to form the filaments and biofilms associated with active infection. This is one reason some women seem to get yeast infections repeatedly while others rarely do, even with similar lifestyles.