Yeast infections happen when a fungus called Candida, which naturally lives in the vagina in small amounts, grows out of control. About 75% of women will experience at least one yeast infection in their lifetime, and understanding what triggers that overgrowth is the key to preventing it. The causes range from medications and hormonal shifts to everyday habits you might not think twice about.
Candida is present in the vaginas of 10% to 20% of women at any given time without causing any symptoms. It only becomes an infection when something disrupts the balance between Candida and the protective bacteria that normally keep it in check.
Antibiotics Are the Most Common Trigger
Antibiotics kill bacteria, and that includes the beneficial bacteria in the vagina that suppress Candida growth. When those protective bacteria are wiped out, yeast has room to multiply rapidly. This is why yeast infections frequently show up during or shortly after a course of antibiotics, even ones prescribed for something completely unrelated like a sinus infection or urinary tract infection. The broader the antibiotic (meaning it targets many types of bacteria), the higher the risk.
Hormonal Changes That Fuel Yeast Growth
Elevated estrogen levels create conditions that favor Candida. Higher estrogen increases the amount of glycogen (a sugar the body stores in cells) in vaginal tissue, which essentially feeds the yeast. This is why yeast infections are more common during pregnancy, when estrogen levels surge dramatically. Hormonal birth control pills carry the same risk, particularly higher-dose formulations.
The hormonal fluctuations around your menstrual cycle can also play a role. Some women notice recurring infections at the same point in their cycle each month, typically in the days before their period when hormone levels shift.
Moisture, Heat, and What You Wear
Candida thrives in warm, moist environments. Synthetic fabrics like nylon and spandex trap heat and moisture against the skin, creating ideal conditions for yeast to multiply. Cotton underwear, by contrast, allows air to circulate and moisture to evaporate. Sitting in a wet swimsuit or sweaty workout clothes for extended periods has the same effect: you’re giving yeast exactly the environment it prefers.
Tight-fitting clothing compounds the problem by reducing airflow to the groin area. Switching to looser pants and breathable fabrics, especially in warmer weather or after exercise, can make a noticeable difference for people who get frequent infections.
Douching and Scented Products
Vaginal douching increases the risk of yeast infections roughly fourfold. Douching flushes out the protective bacteria that keep Candida in check, leaving the vaginal environment vulnerable to overgrowth. The vagina is self-cleaning, and introducing water, vinegar, or commercial douching solutions disrupts that natural process.
Scented tampons, pads, and feminine sprays pose a similar risk. Fragrances, essential oils (including lavender, mint, and aloe vera), chlorine, and titanium dioxide can all irritate vaginal tissue and disrupt the balance of bacteria and pH levels. Unscented, fragrance-free products are the safer choice for anything that contacts the vulva or vagina.
Weakened Immune System
Your immune system normally helps keep Candida populations small. When that system is compromised, yeast has an easier time overgrowing. The CDC lists several conditions that raise the risk: HIV/AIDS, cancer (particularly blood cancers like leukemia and lymphoma), and diabetes. Uncontrolled diabetes is an especially significant risk factor because elevated blood sugar provides extra fuel for yeast, both in the vagina and elsewhere in the body.
Medications that suppress immune function also increase vulnerability. Corticosteroids, including inhaled steroids used for asthma, and chemotherapy drugs both reduce the body’s ability to control Candida. If you’re on long-term immunosuppressive treatment and experiencing recurrent infections, that connection is worth discussing with your provider.
Can You Get a Yeast Infection From Sex?
Candida is not classified as a sexually transmitted infection because it naturally exists in the body. That said, it can sometimes pass between partners during sex. The research on this is somewhat counterintuitive: being married or having a steady sexual partner more than doubles the risk of transmission, while having many sexual partners does not appear to increase a woman’s risk. Studies have also found no clear link between oral sex and yeast infections, and no evidence of Candida transmission between women in steady same-sex relationships.
Male partners with balanitis (inflammation of the head of the penis) can harbor high concentrations of Candida, and poor hygiene plays a major role in that condition. If you’re getting recurrent infections and your partner has symptoms like redness, irritation, or a rash on the penis, treating both partners may help break the cycle.
Why Some People Get Recurring Infections
Recurrent yeast infections, defined as four or more episodes in a single year, affect a significant number of women. What makes this frustrating is that the cause is often unclear. The CDC notes that the majority of women with recurrent infections have no obvious predisposing condition. Their immune systems are healthy, they aren’t on antibiotics, and no single identifiable trigger explains the pattern.
For those who can identify a trigger, addressing it directly is the most effective prevention strategy: switching to cotton underwear, stopping douching, changing birth control methods, or managing blood sugar more tightly if diabetic. For those without an identifiable cause, longer courses of antifungal treatment or suppressive therapy can reduce the frequency of episodes. Importantly, finding Candida on a routine culture without any symptoms is not a reason for treatment. Carrying the yeast without symptoms is normal and common.