Yeast infections are caused by an overgrowth of Candida, a fungus that naturally lives in your body in small amounts. About 75% of women will experience at least one vaginal yeast infection in their lifetime, and the triggers range from medications and hormonal shifts to everyday habits like the underwear you choose.
The most common species involved is Candida albicans. Under normal conditions, it coexists peacefully with protective bacteria in the vagina. But when something disrupts that balance, Candida shifts into a more aggressive, thread-like form that produces a toxin called candidalysin, which damages surrounding cells and triggers inflammation. That’s when symptoms like itching, burning, and thick discharge appear.
How Protective Bacteria Keep Yeast in Check
Your vagina maintains a slightly acidic environment, largely thanks to Lactobacillus bacteria. These bacteria produce lactic acid and other compounds that suppress Candida growth and prevent it from gaining a foothold. When Lactobacillus populations drop, the vaginal pH rises, and yeast has the opening it needs to multiply.
Nearly every cause of yeast infections traces back to this same core mechanism: something knocks out the protective bacteria, weakens your immune response, or creates conditions that let Candida thrive. The specific triggers fall into several categories.
Antibiotics
Broad-spectrum antibiotics are one of the most common causes of yeast infections. These drugs don’t distinguish between harmful bacteria and the beneficial Lactobacillus in your vagina. When antibiotics wipe out that protective flora, yeast faces less competition and proliferates quickly. A significant number of women develop candidiasis during or shortly after a course of antibiotics, and the resulting disruption can also increase susceptibility to reinfection by resistant organisms.
If you’re prescribed antibiotics for a bacterial infection, this doesn’t mean you should skip them. But it helps to be aware that a yeast infection may follow, so you can recognize the symptoms early.
Hormonal Changes
Estrogen plays a direct role in yeast infection risk. High estrogen levels increase glycogen (a type of sugar) in vaginal tissue, which feeds Candida. This is why yeast infections are more common during pregnancy, in the second half of the menstrual cycle, and among women taking hormonal birth control with higher estrogen doses.
Vaginal estrogen therapy, sometimes prescribed during menopause to treat dryness and irritation, can also trigger yeast overgrowth for the same reason. The hormone itself creates a more hospitable environment for the fungus. Women going through perimenopause may notice a pattern of infections that aligns with their fluctuating hormone levels.
Uncontrolled Blood Sugar
Diabetes is a well-established risk factor for yeast infections. When blood sugar runs high, excess glucose shows up in vaginal secretions and urine, essentially providing a steady food supply for Candida. The CDC notes that elevated blood sugar encourages both yeast and bacteria to grow in the genital area.
This connection isn’t limited to people with diagnosed diabetes. Any condition or dietary pattern that keeps blood sugar consistently elevated can increase your risk. Women with poorly controlled type 1 or type 2 diabetes often experience recurrent yeast infections, defined as four or more episodes in a single year. Getting blood sugar under better control typically reduces the frequency of infections.
A Weakened Immune System
Your immune system is what normally prevents Candida from shifting into its harmful form. When immune function is suppressed, the body loses its ability to contain the fungus. HIV is the most well-known example, but it’s far from the only one.
Systemic corticosteroids (medications like prednisone used for conditions such as asthma, lupus, or inflammatory bowel disease) increase susceptibility to fungal infections through multiple pathways. They affect how white blood cells function and can even directly influence Candida’s growth and ability to cause damage. Chemotherapy, organ transplant medications, and other immunosuppressive treatments carry similar risks. People on long-term steroid therapy are particularly vulnerable to recurrent infections.
Douching and Scented Products
Douching remains surprisingly common, with estimates suggesting 27% to 59% of women practice it. The impact on vaginal health is significant. In one study, 22.2% of women who douched tested positive for bacterial vaginosis compared to just 7.9% of women who didn’t. While bacterial vaginosis and yeast infections are different conditions, both stem from disrupted vaginal flora, and both become more likely when the natural bacterial balance is disturbed.
Scented soaps, bubble baths, vaginal sprays, and scented tampons or pads can cause similar disruption. These products introduce chemicals that irritate vaginal tissue and alter its pH. The vagina is self-cleaning, and most gynecologists recommend washing only the external area with mild, unscented soap or water alone.
Moisture and Clothing Choices
Candida thrives in warm, dark, moist environments. Sitting in a wet bathing suit, wearing sweaty workout clothes for hours, or choosing tight synthetic underwear all create exactly those conditions. The trapped moisture and heat give yeast an ideal environment to multiply.
Simple changes can reduce this risk: switch out of wet swimwear or exercise clothes promptly, choose cotton underwear (or at least cotton-lined), and opt for looser-fitting pants or skirts when possible, especially in warmer months. Moisture-wicking athletic fabrics help moisture evaporate faster during exercise.
Diet and Sugar Intake
The relationship between dietary sugar and yeast infections isn’t as straightforward as some wellness sites suggest, but there is a connection. Yeast feeds on sugar, and diets high in simple sugars and refined carbohydrates can contribute to recurring infections, particularly in women who are already prone to them.
Some practitioners recommend a “Candida diet” that limits white flour, white rice, foods fermented with yeast, and foods high in simple sugars. The evidence behind strict elimination diets is limited, but cutting back on refined sugar in moderate amounts may help reduce the frequency of infections, especially when combined with other lifestyle changes.
Other Contributing Factors
Several less obvious factors can also set the stage for a yeast infection. Stress affects immune function, and chronic stress can make you more susceptible. Sleep deprivation has a similar effect. Sexual activity doesn’t cause yeast infections directly (they’re not considered sexually transmitted), but friction and the introduction of new bacteria can sometimes tip the balance. Spermicides and certain lubricants may also irritate vaginal tissue.
For some women, yeast infections seem to appear without an identifiable trigger. Recurrent vulvovaginal candidiasis, four or more episodes per year, affects a subset of women and may involve genetic differences in immune response rather than any particular behavior or exposure. If you’re dealing with frequent infections despite addressing the common causes, that pattern itself is worth discussing with a healthcare provider, as treatment approaches for recurrent cases differ from one-time infections.