About 75% of women will get at least one vaginal yeast infection in their lifetime, and up to 45% will get two or more. So if you’re dealing with one right now, you’re far from alone. The reason it happened comes down to a shift in the balance of organisms that naturally live in your vagina. A type of yeast called Candida is a normal resident there, but when something disrupts the environment that keeps it in check, the yeast multiplies and causes symptoms.
Understanding what tipped that balance helps you make sense of what’s happening and, more importantly, how to avoid it next time.
How Yeast Overgrows in the First Place
Your vagina naturally contains both bacteria and yeast. In a healthy state, beneficial bacteria (particularly a species called Lactobacillus crispatus) form a protective layer along the vaginal walls and produce acid that keeps the environment at a pH between 3.8 and 4.5. That acidity suppresses the growth of yeast and other potential troublemakers. Lactobacillus essentially starves Candida of resources and blocks its ability to shift into a more aggressive form.
When something reduces the number of these protective bacteria or changes the vaginal environment, Candida gets room to grow. The yeast can then switch from a harmless, round cell form into elongated filaments that burrow into the vaginal lining. It can also form a sticky layer called a biofilm that makes it harder for your body (and antifungal treatments) to clear it. That transition from quiet resident to active infection is what causes the itching, burning, and thick white discharge.
Antibiotics Are the Most Common Trigger
If your yeast infection started during or shortly after a course of antibiotics, that’s almost certainly the connection. Antibiotics are designed to kill bacteria, but they can’t distinguish between the harmful bacteria causing your sinus infection or UTI and the beneficial Lactobacillus keeping your vagina healthy. When those protective bacteria are wiped out, the acidic environment weakens, and Candida fills the gap.
Broad-spectrum antibiotics, the kind prescribed for a wide range of infections, carry the highest risk because they kill the widest variety of bacteria. This doesn’t mean you should skip antibiotics when you need them, but it does explain why a yeast infection can show up as an unwelcome side effect of treating something else entirely.
Hormonal Shifts and Estrogen
Estrogen plays a direct role in the vaginal ecosystem. It stimulates the cells lining the vagina to produce glycogen, a sugar compound that feeds Lactobacillus. When estrogen is high, there’s more glycogen, more Lactobacillus, and a stable acidic environment. But this system is sensitive to change.
Pregnancy raises estrogen levels significantly, which sounds like it should help, but the surge can actually create conditions that favor yeast overgrowth. Hormonal birth control, especially high-estrogen formulations, has a similar effect. On the other end of the spectrum, menopause drops estrogen levels so low that the vaginal lining loses glycogen. Without that food source, Lactobacillus populations decline, the pH rises, and yeast can take over more easily.
Even normal fluctuations during your menstrual cycle can make you more susceptible at certain times of the month. Many women notice yeast infections tend to crop up in the week before their period, when hormonal shifts are most dramatic.
High Blood Sugar Feeds Yeast Directly
If you have diabetes or prediabetes, elevated blood sugar is a significant risk factor. When blood sugar runs high, excess sugar shows up in vaginal secretions and urine, essentially giving Candida an extra food supply. The CDC specifically identifies diabetes as a risk factor for vaginal yeast infections, and poorly controlled blood sugar makes the problem worse.
This connection also works in reverse as a clue. If you’re getting yeast infections frequently and don’t have another obvious trigger, it may be worth checking your blood sugar levels. Recurrent infections are sometimes the first sign that blood sugar isn’t being managed well.
Products That Disrupt Your Vaginal Balance
Your vagina is self-cleaning, but a lot of products marketed for “feminine hygiene” can actually do more harm than good. Douches, vaginal steams, scented washes, and even some lubricants can alter your vaginal pH and kill off protective bacteria. According to Mayo Clinic gynecologists, there’s no need to use douching products, and vaginal steams or herbal inserts can directly affect the bacterial balance that keeps yeast in check.
Semen also temporarily raises vaginal pH, which is why some women notice infections after unprotected sex. Even boric acid suppositories, sometimes recommended for yeast infections, can irritate the vaginal lining and disrupt its natural flora if overused. The simplest approach to vaginal hygiene is warm water on the external area and nothing inside.
A Weakened Immune System
Your immune system normally keeps Candida populations small, even when the vaginal environment shifts slightly. But anything that weakens your immune response, whether that’s HIV, cancer treatment, long-term steroid use, or chemotherapy, reduces your body’s ability to control yeast growth. Corticosteroids, including inhaled steroids for asthma, are a commonly overlooked trigger.
Chronic stress and sleep deprivation also suppress immune function over time. While a single bad night won’t cause a yeast infection, prolonged periods of running yourself down can lower your body’s defenses enough to make infections more likely.
How to Tell It’s Actually a Yeast Infection
Not every itch or unusual discharge is a yeast infection, and treating the wrong thing can make the actual problem worse. Two conditions in particular are easy to confuse.
Yeast infections typically produce thick, white, odorless discharge, sometimes described as resembling cottage cheese. Itching and burning are usually the dominant symptoms, and the vulva may appear red or swollen. Bacterial vaginosis (BV), on the other hand, produces thinner, grayish, foamy discharge with a noticeable fishy smell. BV requires a different treatment entirely, so the distinction matters.
If you’ve had a yeast infection before and the symptoms feel identical, over-the-counter antifungal treatments are reasonable. But if this is your first time, if the symptoms are different from what you’ve experienced before, or if treatment isn’t working, getting a proper diagnosis prevents you from cycling through the wrong remedies.
Why It Keeps Coming Back
Some women deal with yeast infections over and over. Clinically, having multiple episodes within a year is considered recurrent vulvovaginal candidiasis, and it affects a substantial number of women since 40 to 45% will have at least two infections. Recurrent infections involve specific behaviors of the Candida organism itself: the yeast forms biofilms that resist treatment and can persist at low levels even after symptoms clear.
Research has also found that women with recurrent infections tend to have lower levels of the most protective Lactobacillus species and higher levels of a less helpful species called Lactobacillus iners, which is associated with a less stable vaginal environment. Genetic differences in immune response also play a role, meaning some women are simply more prone to yeast infections regardless of what they do.
If you’re dealing with frequent infections, identifying and addressing your specific triggers (antibiotics, blood sugar, hormonal contraception, hygiene products) is the most effective long-term strategy. In many cases, a combination of factors rather than a single cause is what keeps the cycle going.