A yeast infection happens when a fungus called Candida, which normally lives in small amounts in the vagina, multiplies beyond what the body can keep in check. About 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 introduced from outside the body in most cases. It’s already there, waiting for conditions to shift in its favor.
What Candida Needs to Overgrow
Your vagina naturally hosts a mix of bacteria and fungi. The dominant bacteria, called lactobacilli, produce lactic acid that keeps the environment acidic, typically at a pH between 3.8 and 4.5. This acidity suppresses Candida and other potential troublemakers. A yeast infection develops when something disrupts that balance, giving Candida room to multiply rapidly.
Several things can tip the scales. The most common is antibiotics. Because antibiotics kill bacteria broadly, they can wipe out the protective lactobacilli along with whatever infection they were prescribed for. With fewer bacteria producing acid and competing for space, Candida faces less resistance and begins to grow. This is why yeast infections so often follow a course of antibiotics for a sinus infection, urinary tract infection, or other unrelated illness.
How Hormones Play a Role
Estrogen influences the vaginal environment by affecting how cells store glycogen, a sugar that feeds both bacteria and yeast. Higher estrogen levels, such as during pregnancy, while taking oral contraceptives, or during certain phases of the menstrual cycle, change the nutrient landscape inside the vagina. The relationship between estrogen and glycogen is more complex than once thought (research suggests the link isn’t as straightforward as “more estrogen equals more glycogen”), but hormonal shifts clearly correlate with yeast infection timing.
Pregnancy is one of the strongest hormonal risk factors. Estrogen levels rise dramatically, and the immune system partially suppresses itself to protect the fetus. Both of these changes create a more hospitable environment for Candida. Many women who never had a yeast infection before will experience their first one during pregnancy.
Immune System and Blood Sugar
Your immune system normally keeps Candida populations small. Anything that weakens immune function can allow overgrowth. HIV, immunosuppressive medications taken after organ transplants, and chemotherapy all raise the risk significantly. Even chronic stress and poor sleep, which modestly suppress immune responses, can make infections more likely in people who are already prone to them.
Diabetes is another major risk factor, particularly when blood sugar is poorly controlled. Elevated glucose in the blood translates to elevated glucose in vaginal secretions, essentially giving Candida extra fuel. Women with uncontrolled type 2 diabetes experience yeast infections at notably higher rates, and recurrent yeast infections in someone without other obvious risk factors sometimes prompt doctors to screen for diabetes.
Moisture, Clothing, and Daily Habits
Candida thrives in warm, moist environments. Anything that traps heat and moisture against the vulva creates better growing conditions. Tight-fitting synthetic underwear, leggings worn for extended periods after exercise, and wet swimsuits all contribute. Cotton underwear wicks away excess sweat and moisture that yeast thrive on. Even underwear made from synthetic fabric with a cotton crotch panel doesn’t fully protect you, because the surrounding material still limits airflow.
Douching is another common disruptor. It washes away the protective bacteria and alters vaginal pH, which can trigger both yeast infections and bacterial vaginosis. Scented soaps, bubble baths, and vaginal deodorants can have a similar effect by irritating the vaginal lining and disturbing the microbial balance.
What a Yeast Infection Feels Like
The hallmark symptoms are intense itching and irritation of the vulva and vaginal opening. Most women also notice a thick, white discharge that’s often compared to cottage cheese. It typically doesn’t have a strong odor, which is one way to distinguish it from bacterial vaginosis (which produces a fishy smell). Burning during urination and pain during sex are also common, caused by inflammation of the irritated tissue.
Symptoms can range from mild itching to severe swelling and redness that makes sitting uncomfortable. The severity often depends on how long the infection has been developing and whether the skin has become cracked or raw from scratching.
Not All Yeast Infections Are the Same
Most vaginal yeast infections are caused by Candida albicans, which responds well to standard antifungal treatments available over the counter. But other species can cause infections too. Candida glabrata is the second most common species in North America and is naturally less responsive to the most widely used antifungal medications. If you’ve treated a suspected yeast infection with an over-the-counter product and symptoms persist, a non-albicans species could be the reason. These infections typically require different medications that a doctor can prescribe after confirming the species through a lab test.
Why Some People Get Them Repeatedly
Recurrent yeast infections, defined as three or more symptomatic episodes in a single year, affect fewer than 5% of women. For some, there’s a clear trigger: a recurring antibiotic prescription, ongoing hormonal contraceptive use, or unmanaged diabetes. For others, the cause is harder to pin down. Some women appear to have a genetic predisposition that makes their immune system less effective at controlling Candida specifically, even while functioning normally in every other respect.
Recurrent infections can also develop when a previous infection wasn’t fully cleared. Using a treatment course that’s too short or stopping early because symptoms improve can leave enough Candida alive to rebound within weeks. If you’re experiencing recurrent infections, getting a confirmed diagnosis (rather than self-treating) matters, because roughly half of women who assume they have a yeast infection based on symptoms alone actually have something else, like bacterial vaginosis or contact dermatitis, which require completely different treatment.
The Basics of Treatment
Uncomplicated yeast infections are treated with antifungal medications, available as vaginal creams, suppositories, or a single oral pill. Over-the-counter options work well for most first-time or occasional infections caused by Candida albicans. Symptoms typically begin improving within two to three days, with full resolution within a week.
For recurrent infections, treatment usually involves a longer initial course followed by a maintenance regimen, often a weekly oral antifungal for six months. This approach reduces recurrence significantly, though some women experience infections again once they stop maintenance therapy. Identifying and addressing underlying triggers, whether that’s switching contraceptive methods, improving blood sugar control, or changing clothing habits, makes a meaningful difference in long-term outcomes.