About 75% of women will get at least one vaginal yeast infection in their lifetime, and up to 45% will get two or more. Yeast infections happen when a fungus called Candida, which normally lives in small amounts in the vagina, grows out of control. Understanding what triggers that overgrowth can help you avoid repeat infections.
What Causes Yeast to Overgrow
A healthy vagina contains a mix of bacteria and a small amount of yeast. Beneficial bacteria, especially a species called Lactobacillus, keep the environment acidic and compete with yeast for space on the vaginal walls. This balance keeps Candida in check.
When something disrupts that balance, Candida can shift from a harmless form into a more aggressive one that multiplies rapidly and penetrates vaginal tissue. The disruption can come from inside your body (hormonal shifts, a weakened immune system) or from external factors (medications, hygiene habits). In many cases, a yeast infection isn’t caused by a single trigger but by a combination of factors tipping the scales at the same time.
Antibiotics Are a Leading Trigger
Antibiotics kill bacteria, but they don’t distinguish between harmful bacteria and the protective Lactobacillus in your vagina. When a course of antibiotics wipes out those beneficial bacteria, yeast loses its main competitor and can multiply freely. This is one of the most common reasons women develop a yeast infection seemingly out of nowhere. It can happen with any antibiotic, whether you’re taking it for a sinus infection, a urinary tract infection, or anything else.
Hormonal Changes and Estrogen
Elevated estrogen levels change the vaginal environment in ways that favor yeast growth. Higher estrogen increases glycogen (a type of sugar) in the vaginal lining, which can feed Candida. Several situations raise estrogen levels significantly:
- Pregnancy: Estrogen rises steadily throughout pregnancy, making yeast infections especially common in the second and third trimesters.
- Hormonal birth control: Pills, patches, or rings that contain estrogen can shift the vaginal ecosystem enough to encourage yeast overgrowth in some women.
- Hormone replacement therapy: Estrogen-based treatments used during menopause carry a similar effect.
Not every woman on birth control or going through pregnancy will get a yeast infection, but these hormonal shifts are a well-documented risk factor.
High Blood Sugar Feeds Yeast
Women with uncontrolled or poorly managed diabetes are at higher risk for recurrent yeast infections. When blood sugar stays elevated, excess sugar can show up in vaginal secretions and urine, creating a rich food source for Candida. If you’re getting yeast infections frequently and haven’t had your blood sugar checked recently, it’s worth looking into. Getting blood sugar under better control often reduces the frequency of infections.
Weakened Immune System
Your immune system plays a central role in keeping vaginal yeast in its harmless state. Conditions or treatments that suppress immune function, such as HIV, chemotherapy, or long-term corticosteroid use, remove one of the body’s key defenses against Candida overgrowth. Women who are otherwise healthy but under significant physical stress (recovering from surgery, fighting off another illness) may also be more susceptible.
Douching and Scented Products
Douching is one of the clearest lifestyle-related risk factors. It strips away the normal bacteria that protect against infection and disrupts the vagina’s naturally acidic pH. That acidic environment is your body’s built-in defense, and flushing it out gives yeast room to take over. The vagina is self-cleaning, so douching offers no health benefit and carries real risk.
Scented tampons, pads, sprays, and powders can cause similar problems. These products introduce chemicals that irritate vaginal tissue and alter the microbial balance. Switching to unscented products is a simple change that can make a real difference for women prone to infections.
Moisture and Clothing Choices
Yeast thrives in warm, moist environments. Sitting in a wet swimsuit, wearing sweaty workout clothes for hours, or choosing underwear made from synthetic fabrics all create conditions that encourage fungal growth. Cotton underwear is breathable and wicks moisture away from the skin, making it significantly better for vaginal health. Underwear labeled as having a “cotton crotch panel” in an otherwise synthetic garment doesn’t provide the same level of protection, since the synthetic fabric still traps heat and moisture around the surrounding area.
Tight-fitting pants and leggings can compound the problem by reducing airflow. If you’re dealing with recurrent infections, switching to looser, more breathable clothing, especially during warmer months, is a practical step.
Can You Get a Yeast Infection From Sex
A yeast infection is not classified as a sexually transmitted infection because you can develop one without any sexual contact. That said, it is possible to get a yeast infection from a sexual partner. Condoms and dental dams can help reduce the risk of passing yeast between partners during vaginal, oral, or anal sex.
If your partner is male, his risk of developing symptoms is relatively low. About 15% of men develop an itchy rash on the penis after unprotected sex with a woman who has an active yeast infection. If your partner is female, the risk of transmission is higher, and she should get tested if she develops symptoms. In couples where yeast infections keep bouncing back and forth, treating both partners at the same time can help break the cycle.
Why Some Women Get Them Repeatedly
For some women, yeast infections are a one-time inconvenience. For others, they come back four or more times a year, a pattern known as recurrent vulvovaginal candidiasis. Recurrent infections often involve the same underlying triggers: ongoing antibiotic use, persistent hormonal changes, chronically elevated blood sugar, or an immune system that isn’t functioning at full capacity. Sometimes, the specific strain of Candida involved is naturally harder for the body to control.
If you’re dealing with frequent infections, identifying and addressing the root cause is more effective than simply treating each episode as it comes. Tracking when infections happen in relation to your menstrual cycle, medications, or lifestyle habits can reveal a pattern that points to the primary trigger.