Yeast infections happen when a fungus that already lives in your body grows out of control. About 75% of women will have at least one vaginal yeast infection in their lifetime, and 40% to 45% will deal with two or more. The triggers range from medications and hormonal shifts to everyday habits you might not suspect.
How a Yeast Infection Starts
A yeast called Candida albicans naturally lives on your skin and inside your body, including in the vagina and digestive tract. Normally, healthy bacteria keep this yeast in check by maintaining an acidic environment where Candida can’t multiply freely. A yeast infection develops when something disrupts that bacterial balance and gives the yeast room to overgrow.
Almost anything that shifts your body’s internal chemistry, weakens your immune defenses, or changes conditions in the vaginal environment can tip the scale. The sections below cover the most common culprits.
Antibiotics
Antibiotics are one of the most well-established triggers. They work by killing bacteria, but they don’t distinguish between the harmful bacteria causing your illness and the beneficial bacteria keeping Candida in check. When those protective bacteria are wiped out, yeast can multiply rapidly in the gap they leave behind.
Research published in Cell Host & Microbe found that antibiotics enhanced susceptibility to invasive fungal infection by disrupting immune signaling in the gut. Even a single type of antibiotic was enough to increase fungal overgrowth and impair the body’s antifungal defenses. This is why yeast infections commonly show up during or right after a course of antibiotics, whether you took them for a sinus infection, a UTI, or anything else.
Hormonal Changes
Estrogen plays a direct role in yeast growth. High estrogen levels increase the amount of glycogen (a type of sugar) stored in vaginal tissue, which feeds Candida. This is why yeast infections are more common during pregnancy, when estrogen surges dramatically. Hormonal birth control that contains estrogen can have a similar effect.
The connection works in both directions. During menopause, fluctuating hormone levels can also alter vaginal chemistry enough to trigger recurrent infections in some women. Any major hormonal shift, whether from a new contraceptive, pregnancy, or a phase of your menstrual cycle, can change your susceptibility.
Diabetes and High Blood Sugar
Yeast feeds on sugar, so chronically elevated blood sugar creates an ideal environment for Candida to thrive. If you have diabetes, especially when blood sugar levels aren’t well controlled, several things work against you at once. The excess sugar in your blood and tissues gives yeast more fuel to grow. High blood sugar also changes vaginal pH, making it less acidic and less hostile to fungal overgrowth. On top of that, diabetes can weaken your immune system’s ability to fight off infections.
Certain diabetes medications that work by flushing excess sugar out through your urine can also increase yeast infection risk, because they concentrate sugar in the urinary and genital tract. If you notice frequent yeast infections and haven’t had your blood sugar checked recently, that’s worth looking into.
Douching and Scented Products
The vagina is self-cleaning, and douching disrupts the bacterial balance that keeps it healthy. Douching washes away the protective bacteria and changes the natural acidity of the vaginal environment. With those defenses removed, harmful organisms including yeast can overgrow. The U.S. Office on Women’s Health directly links douching to increased risk of yeast infections and bacterial vaginosis.
Scented tampons, pads, powders, and sprays can cause similar problems. These products introduce chemicals that irritate vaginal tissue and alter the microbial balance. Even mild soaps can cause dryness and irritation for those with sensitive skin or an existing infection. Plain water, or at most an unscented, gentle cleanser on the external area only, is all that’s needed.
Tight or Synthetic Clothing
Candida thrives in warm, moist environments. Tight-fitting clothing made from synthetic materials like nylon and spandex traps heat and moisture against the skin, creating exactly those conditions. Cotton underwear is breathable and absorbent, which helps keep the area dry and less hospitable to yeast.
This matters most during exercise and overnight. Moisture-wicking underwear is a better choice for workouts, and sleeping without underwear can help the area breathe and prevent moisture buildup. If you deal with recurring infections, these small changes in what you wear can make a noticeable difference.
Diet
There’s a reason “Candida diets” have gained attention. Yeast feeds on simple sugars, and a diet high in refined sugar, white flour, and white rice may contribute to recurring infections. Some practitioners recommend reducing foods made with yeast, fermented foods, and simple sugars to limit the fuel available for Candida growth.
You don’t necessarily need to eliminate these foods entirely. Even modest reductions in sugar intake, combined with eating more whole grains, vegetables, and protein, can shift the balance. The connection between dietary sugar and yeast infections is strongest when blood sugar levels are consistently elevated, so this overlaps heavily with the diabetes risk factor.
Sexual Activity
A yeast infection is not a sexually transmitted infection, because you can develop one without any sexual contact. However, it is possible to pass yeast to a partner during vaginal, oral, or anal sex. About 15% of men develop an itchy rash on the penis after unprotected sex with a woman who has an active yeast infection.
Sex can also trigger yeast infections indirectly. Semen is alkaline, which temporarily raises vaginal pH and can disrupt the acidic environment that keeps Candida in check. Lubricants and spermicides may contain ingredients that irritate vaginal tissue. Condoms and dental dams reduce the risk of passing yeast between partners.
A Weakened Immune System
Your immune system is the last line of defense against Candida overgrowth. Anything that suppresses immune function, including HIV, chemotherapy, organ transplant medications, or long-term corticosteroid use, raises your risk significantly. Chronic stress and sleep deprivation also dampen immune responses, though their effect is less dramatic than immunosuppressive medications.
When the immune system is severely compromised, Candida can cause more than a surface-level vaginal or skin infection. It can enter the bloodstream and become invasive, which is a serious medical condition primarily seen in hospitalized patients. For most people, though, the concern is simply that a run-down immune system makes ordinary yeast infections more frequent and harder to resolve.
Multiple Triggers at Once
Yeast infections rarely have a single, clean cause. More often, several factors stack up. You take antibiotics for bronchitis, you’re stressed and sleeping poorly, and you’ve been wearing leggings to the gym every day. Each factor nudges the balance a little further in favor of Candida, and together they tip it over the edge. If you get yeast infections frequently, identifying which combination of triggers applies to you is the most effective way to reduce them. Keeping a simple log of when infections happen and what preceded them (medications, cycle timing, diet changes, clothing choices) can reveal patterns that aren’t obvious in the moment.