Yeast infections occur when a fungus called Candida, which normally lives in small amounts in the vagina, multiplies beyond what the body can keep in check. An estimated 75% of women will experience at least one yeast infection in their lifetime, and 40% to 45% will have two or more. The infection isn’t usually caused by exposure to something new. It’s caused by a shift in conditions that lets an organism already present gain the upper hand.
What Happens Inside the Body
A healthy vagina contains a mix of bacteria and a small population of Candida yeast. Beneficial bacteria, particularly a type called Lactobacillus, keep the environment acidic (a pH of roughly 4.0 to 4.5 during reproductive years). That acidity suppresses yeast growth and keeps the microbial community in balance.
When something disrupts that balance, Candida cells begin to multiply rapidly. More importantly, the yeast undergoes a physical transformation. Individual round cells shift into long, branching, tube-like structures that can penetrate the vaginal lining. This shape change, triggered by shifts in temperature, pH, and the local chemical environment, is what turns harmless yeast into an active infection. The branching structures invade tissue and form dense colonies called biofilms, which is why symptoms can feel so persistent once they take hold.
Common Triggers
Antibiotics
Broad-spectrum antibiotics are one of the most common triggers. These drugs don’t just kill the bacteria causing your sinus infection or bronchitis. They also wipe out the Lactobacillus bacteria that maintain vaginal acidity. Without that protective population, the vaginal environment becomes less acidic and more hospitable to yeast. A yeast infection can develop during or shortly after finishing a course of antibiotics.
Hormonal Changes
High estrogen levels increase the amount of glycogen (a type of sugar) stored in vaginal cells. While Lactobacillus bacteria feed on glycogen to produce the acid that keeps yeast in check, elevated estrogen can tip the balance too far, fueling yeast overgrowth. This is why yeast infections are more common during pregnancy, while taking birth control pills with higher estrogen doses, or after starting vaginal estrogen therapy during menopause.
Menopause creates a different kind of vulnerability. As estrogen drops, vaginal cells lose glycogen. Lactobacillus populations decline because they depend on glycogen for fuel, and the loss of those protective bacteria can open the door to yeast overgrowth from the opposite direction.
Elevated Blood Sugar
Poorly controlled diabetes creates conditions that favor yeast at the cellular level. Higher glucose concentrations in vaginal tissue increase the ability of Candida cells to stick to and invade the tissue lining. Sugar also enhances several of the yeast’s survival mechanisms, including its ability to resist the immune system and tolerate antifungal treatments. If you notice recurring infections and haven’t had your blood sugar checked recently, it’s worth a conversation with your doctor.
Other Contributing Factors
- Weakened immune system: Conditions or medications that suppress immune function give Candida more room to grow unchecked.
- Moisture and warmth: Tight, non-breathable clothing or sitting in wet swimwear creates an environment where yeast thrives.
- Douching or fragranced products: These can disrupt the vaginal bacterial balance much the way antibiotics do, removing protective bacteria.
What a Yeast Infection Feels Like
The hallmark symptom is itching, often intense, around the vulva and vaginal opening. Many people also experience a thick, white discharge that looks like cottage cheese and has little to no odor. The lack of a strong smell is actually one of the distinguishing features. Bacterial infections of the vagina typically produce a fishy odor, while yeast infections generally do not. Burning during urination or sex, redness, and swelling of the vulvar tissue are also common.
Not every case looks the same. Some infections cause heavy discharge with minimal itching, while others cause significant irritation with almost no discharge. Mild infections may involve only slight discomfort, while severe ones can cause cracking or tiny tears in the skin from swelling and scratching.
How Yeast Infections Are Treated
Most uncomplicated yeast infections respond well to antifungal treatment, either as a single oral dose or as a vaginal cream or suppository used for one to seven days. With a single oral dose, symptoms typically begin improving within one to three days. Over-the-counter vaginal antifungal treatments follow a similar timeline, though multi-day regimens may take slightly longer for full relief.
If you’ve never had a yeast infection before, getting a proper diagnosis matters. The symptoms overlap with bacterial vaginosis and certain sexually transmitted infections, and treating the wrong condition delays relief and can make things worse.
Why Some People Get Recurring Infections
Some people deal with yeast infections four or more times a year, a pattern that affects a meaningful subset of that 40% to 45% who get repeat infections. Recurrence often points to an underlying factor that keeps resetting the conditions for overgrowth: ongoing antibiotic use, hormonal fluctuations, uncontrolled blood sugar, or an immune system that can’t fully suppress the yeast.
In recurrent cases, treatment usually extends beyond a single dose. The goal shifts from clearing one infection to suppressing yeast over a longer period while addressing whatever root cause is enabling the cycle. Identifying and managing the underlying trigger, whether it’s switching a medication, improving blood sugar control, or adjusting a hormonal contraceptive, is often more effective than repeatedly treating individual episodes.