Yeast infections happen when a fungus called Candida, which normally lives in small amounts in your vagina, grows out of control. You didn’t necessarily “catch” it from somewhere. The yeast was almost certainly already there. Something shifted the balance of your vaginal environment and allowed it to multiply. Understanding what that something was can help you avoid it next time.
How Your Vaginal Balance Works
Your vagina hosts a community of bacteria that keep yeast in check. The most important players are Lactobacillus bacteria, which produce lactic acid and maintain an acidic environment (a pH below 4.5) that prevents Candida from growing aggressively. When that bacterial population shrinks or weakens, Candida seizes the opportunity.
Not all protective bacteria are equally effective. Research shows that vaginas dominated by a species called Lactobacillus crispatus are significantly less likely to harbor Candida than those dominated by Lactobacillus iners. L. crispatus produces more lactic acid and inhibits yeast growth more effectively. You can’t control which species you carry, but this helps explain why some people get yeast infections more easily than others, even when their habits are identical.
Antibiotics Are the Most Common Trigger
If you recently finished a course of antibiotics, that’s likely your answer. Antibiotics kill bacteria indiscriminately, wiping out the Lactobacillus that keep yeast in check. This is the single most common trigger for yeast infections.
Not all antibiotics carry the same risk. A 2025 analysis of medical records found that azithromycin (a common antibiotic for respiratory and skin infections) more than doubled the risk of a yeast infection, with doxycycline (frequently prescribed for acne) also raising risk significantly. Azithromycin carried about 66% more risk than doxycycline. Interestingly, minocycline and erythromycin didn’t show a statistically significant increase, suggesting the type of antibiotic matters. If you’re prone to yeast infections and your doctor prescribes antibiotics, it’s worth asking whether a lower-risk option exists.
Hormonal Changes
Estrogen plays a complicated role in vaginal health. It stimulates the vaginal lining to produce glycogen, a sugar that feeds Lactobacillus bacteria and helps maintain acidity. But estrogen also directly affects Candida itself, influencing genes involved in the fungus’s ability to shift into a more aggressive form.
This is why yeast infections cluster around specific life moments. Pregnancy dramatically raises estrogen levels, making yeast infections much more common, especially in the second and third trimesters. Hormonal birth control (particularly higher-estrogen formulations) can do the same. Many people notice infections tend to appear right before their period, when hormone levels shift. If you recently started or changed a hormonal contraceptive, that could be the connection.
Blood Sugar and Diabetes
Candida thrives in high-sugar conditions. When blood glucose is elevated, vaginal secretions contain more sugar, creating a more hospitable environment for yeast. People with type 2 diabetes face a well-documented elevated risk of yeast infections, and poor blood sugar control amplifies that risk further.
You don’t need a diabetes diagnosis for this to apply. Even temporary blood sugar spikes from illness, stress, or steroid medications (like prednisone) can create conditions that favor yeast growth. If you’re getting recurrent yeast infections without an obvious cause, it’s worth checking your blood sugar levels, as repeated infections are sometimes the first sign of undiagnosed diabetes or prediabetes.
Moisture, Clothing, and Hygiene Products
Yeast loves warm, moist environments. Sitting in a wet swimsuit, wearing tight synthetic underwear, or spending long hours in sweaty workout clothes creates ideal conditions for Candida to multiply. Switching to cotton underwear and changing out of damp clothing promptly removes one of the simplest triggers.
Douching is another common culprit. It disrupts the natural bacterial balance and can directly cause yeast overgrowth. Scented tampons, pads, powders, and vaginal sprays carry similar risks. Your vagina is self-cleaning. Plain water on the external area is all it needs.
Can You Get It From Sex?
Yeast infections aren’t classified as sexually transmitted infections, but sex can play a role. About 15% of male partners will develop symptoms of a penile yeast infection after intercourse with someone who has one. Transmission can go both directions, and reinfection from a partner is possible. Oral sex can also introduce yeast.
Sex can trigger a yeast infection even without transmission. Friction, lubricants, spermicides, and condom materials can irritate vaginal tissue and shift the microbial balance. If your infections tend to follow sexual activity, the cause may be mechanical rather than infectious.
Other Contributing Factors
A weakened immune system makes yeast infections more likely. This includes people taking immunosuppressive medications, those undergoing chemotherapy, and people living with HIV. Chronic stress and sleep deprivation can suppress immune function enough to tip the balance as well, though these are harder to quantify.
Diet is often discussed but less clearly supported by evidence. The idea that eating sugar directly causes yeast infections is an oversimplification. What matters is your blood sugar level, not necessarily how much sugar you eat in a given meal (unless it’s raising your blood glucose significantly).
How to Tell It’s Actually a Yeast Infection
Before treating yourself, make sure you’re dealing with the right condition. Yeast infections produce thick, white, odorless discharge, often described as resembling cottage cheese, along with itching, burning, and redness. If your discharge is grayish, foamy, or has a fishy smell, that points to bacterial vaginosis, which requires a completely different treatment. Using antifungal cream for BV won’t help and delays proper care.
A vaginal pH below 4.5 is consistent with a yeast infection, while BV typically raises pH above that threshold. If you’ve never had a yeast infection before, or if over-the-counter treatments aren’t working, getting a proper diagnosis matters. A clinician can examine a sample under a microscope or send a culture to confirm Candida is actually the problem. Studies show that self-diagnosis is wrong roughly half the time.
When Yeast Infections Keep Coming Back
If you’re experiencing four or more yeast infections in a single year, that’s considered recurrent. At that point, over-the-counter treatments alone are unlikely to break the cycle, and longer-term management strategies become necessary. Recurrent infections warrant a clinical evaluation to rule out underlying causes like uncontrolled blood sugar, a resistant Candida species, or an immune issue. A culture can identify the specific yeast species involved, since some respond poorly to standard treatments.