Yeast infections are caused by an overgrowth of a fungus called Candida that already lives on your body. About 75% of women will experience at least one vaginal yeast infection in their lifetime, and 40% to 45% will have two or more. The infection isn’t usually about “catching” something new. It’s about conditions shifting inside your body in ways that let a normally harmless organism multiply out of control.
Candida Already Lives in Your Body
Candida, most commonly the species Candida albicans, is a normal part of your body’s microbial community. It lives on your skin, in your gut, in your mouth, and in the vagina without causing problems. In a healthy person, it exists in a quiet, rounded yeast form that coexists peacefully with other microorganisms and your immune system.
The trouble starts when something disrupts this balance. Candida responds to changes in its environment by shifting its shape, switching from that harmless rounded form into long, thread-like filaments that can penetrate tissue and trigger inflammation. This is what transforms it from a silent resident into an active infection. The organism essentially reads signals from its surroundings, and when conditions favor growth, it ramps up the genes that make it more aggressive.
Antibiotics Are the Most Common Trigger
Your vagina maintains a naturally acidic environment, with a healthy pH between 3.8 and 4.5. This acidity is largely maintained by beneficial Lactobacillus bacteria, which produce lactic acid and keep Candida populations in check. When you take broad-spectrum antibiotics for a bacterial infection elsewhere in your body, those drugs don’t distinguish between harmful bacteria and the protective Lactobacillus in your vagina. The protective bacteria die off, the acidic environment weakens, and Candida seizes the opportunity to multiply.
This is why yeast infections so often follow a course of antibiotics. The antimicrobial therapy eliminates the commensal organisms that were acting as a natural barrier, leaving you more susceptible to fungal overgrowth. It’s also why recurrent yeast infections can become a cycle: treating one infection can sometimes set the stage for the next.
High Blood Sugar Feeds the Fungus
Candida feeds on sugar. When blood glucose levels are elevated, as happens with poorly controlled diabetes, excess sugar can show up in vaginal secretions and urine. This creates a glucose-rich environment where yeast thrives. The CDC lists diabetes as a specific risk factor for vaginal, oral, and invasive forms of candidiasis.
You don’t need to have diabetes for this to matter. Blood sugar spikes from other causes can contribute, though the risk is most significant and well-documented in people with chronically elevated glucose levels.
Hormonal Changes Shift the Environment
Pregnancy, hormonal contraceptives, and the normal fluctuations of your menstrual cycle all change the vaginal environment in ways that can encourage yeast growth. Pregnancy in particular is a well-established risk factor. Rising hormone levels alter the composition of vaginal secretions and may increase glycogen (a form of stored sugar) in vaginal tissue, providing more fuel for Candida.
The relationship between hormones and yeast infections is more complex than it might seem. Research on young women has found that the connection between estrogen levels and vaginal glycogen isn’t as straightforward as once thought, suggesting that hormones influence yeast risk through multiple pathways rather than a single simple mechanism. What’s clear is that times of hormonal change correlate with higher infection rates.
A Weakened Immune System Loses Control
Your immune system is the primary force keeping Candida in its harmless form. Anything that suppresses immune function can tip the balance. HIV/AIDS, cancer, chemotherapy, corticosteroids (including inhaled steroids for asthma), and organ transplant medications all increase the risk of candidiasis. The organism essentially monitors the immune status of its host and shifts toward a more aggressive lifestyle when immune defenses weaken.
Even temporary immune suppression from stress, illness, or lack of sleep can play a role, though the risk is most pronounced with significant, sustained immune compromise.
Moisture and Clothing Create Ideal Conditions
Candida thrives in warm, dark, moist environments. Sitting in a wet bathing suit, exercising in non-breathable synthetic fabrics, or wearing tight underwear all create exactly these conditions. The moisture gets trapped against the skin, raising the local temperature and humidity to levels that promote fungal growth.
Simple changes make a real difference here. Cotton underwear allows more airflow than synthetic materials. Moisture-wicking workout clothes help sweat evaporate faster. Changing out of wet swimwear promptly removes one of the easiest-to-avoid risk factors. Loose-fitting clothing, especially in warmer months, reduces the trapped heat and moisture that Candida depends on.
Douching Disrupts Natural Defenses
Douching is one of the most counterproductive things you can do for vaginal health. A healthy vagina maintains its own balance of bacteria and acidity. Douching washes away the normal protective bacteria and disrupts the acidic pH that keeps harmful organisms in check. According to the Office on Women’s Health, douching can directly cause an overgrowth of harmful bacteria and lead to yeast infections.
The vagina is self-cleaning. The discharge you produce is part of that process. Washing the external area with mild soap and water is sufficient. Internal rinsing removes the very defenses your body uses to prevent infections like candidiasis.
Multiple Factors Often Overlap
In practice, yeast infections rarely have a single clean cause. A person taking antibiotics who also wears tight synthetic underwear and is under significant stress has compounding risk factors. Someone with diabetes who becomes pregnant faces overlapping metabolic and hormonal shifts. Understanding the full range of triggers helps explain why some people get frequent infections while others rarely do, even when their immediate circumstances seem similar.
Recurrent yeast infections, defined as four or more episodes in a year, sometimes involve non-albicans Candida species like Candida glabrata. These species can be more resistant to standard antifungal treatments, which is one reason infections keep returning despite treatment. If you’re dealing with frequent recurrences, the specific type of Candida involved may matter for finding an effective treatment approach.