Yeast infections come from an overgrowth of a fungus called Candida that already lives in your vagina in small amounts. About 75% of women will get at least one yeast infection in their lifetime, and 40% to 45% will have two or more. The fungus isn’t something you “catch” from the outside. It’s a normal part of your vaginal ecosystem that only causes problems when something shifts the balance and lets it multiply out of control.
How Candida Goes From Harmless to Harmful
Candida normally exists in a compact, rounded yeast form that coexists peacefully with the other microorganisms in your vagina. The trouble starts when it shifts into a different shape, sprouting long, branching filaments that can latch onto and burrow into the cells lining your vaginal walls. This shape-shifting is the core event behind every yeast infection. Once in filament form, Candida produces a toxin that punches tiny holes in your cells, causing the irritation, swelling, and discharge you feel as symptoms.
Your immune system detects that damage and sends waves of infection-fighting cells to the area. Ironically, this immune response is responsible for much of the discomfort. The redness, itching, and swelling are largely your own body’s inflammatory reaction to the tissue damage Candida is causing.
What Normally Keeps Candida in Check
The main line of defense is a group of beneficial bacteria called Lactobacillus. These bacteria produce lactic acid that keeps your vaginal pH at around 3.8 to 4.5, an acidic environment that limits Candida’s ability to shift into its harmful filament form. Lactobacillus species also produce compounds like hydrogen peroxide and natural surfactants that directly interfere with Candida’s growth and prevent it from sticking to vaginal tissue.
When this bacterial population is healthy and dominant, Candida stays small and harmless. Nearly every cause of a yeast infection traces back to something that either weakens those protective bacteria, feeds the fungus extra fuel, or suppresses the immune responses that keep it contained.
Antibiotics
Antibiotics are one of the most common triggers. Broad-spectrum antibiotics, the kind prescribed for sinus infections, strep throat, or urinary tract infections, don’t just kill the bacteria making you sick. They also wipe out the Lactobacillus in your vagina. With those protective bacteria diminished, the acidic environment weakens, and Candida faces far less competition. The result is a yeast infection that can show up during or shortly after your antibiotic course. If you’re someone who tends to get yeast infections after antibiotics, it’s worth mentioning that pattern to your doctor before starting a new prescription.
Hormonal Changes
Estrogen has a direct effect on Candida. Higher estrogen levels stimulate the fungus to sprout those harmful filaments more aggressively and grow them longer. This is why yeast infections are more common during pregnancy, when estrogen surges dramatically. Hormonal birth control that raises estrogen levels carries a similar, though smaller, risk. The hormonal fluctuations around your period can also create windows of vulnerability, which is why some women notice a pattern of infections at certain points in their cycle.
High Blood Sugar
Candida feeds on sugar. When blood sugar is elevated, excess glucose shows up in vaginal secretions and urine, essentially giving the fungus extra fuel. This is why yeast infections are significantly more common in women with diabetes, particularly when blood sugar is poorly controlled. Even in women without diabetes, periods of consistently high sugar intake can nudge conditions in Candida’s favor, though the effect is much less dramatic than the impact of actual hyperglycemia.
Hygiene Products That Backfire
Many products marketed for vaginal cleanliness actually increase infection risk. A University of Guelph study found that women using gel sanitizers were eight times more likely to have a yeast infection. Those using lubricants or moisturizers were two and a half times as likely. Feminine washes, wipes, scented tampons, and douches all disrupt the natural bacterial balance and pH that keep Candida suppressed. Soaps and detergents can have the same effect.
The vagina is self-cleaning. Plain warm water on the external vulva is all that’s needed. The American College of Obstetricians and Gynecologists specifically recommends against feminine hygiene sprays, scented tampons, and douching.
A Weakened Immune System
Your immune system actively monitors Candida through a specific pathway involving cells that produce a signaling molecule called IL-17. These cells coordinate the inflammatory response that clears the fungus before it can establish an infection. Anything that suppresses this arm of the immune system raises your risk. That includes HIV, immunosuppressive medications taken after organ transplants, chemotherapy, and chronic stress or sleep deprivation that gradually wears down immune function. Some people have genetic variations that make this particular immune pathway less effective, which helps explain why a small percentage of women (under 5%) experience recurrent infections, defined as three or more episodes in a single year.
Other Contributing Factors
Tight, non-breathable clothing and synthetic underwear trap heat and moisture against the vulva, creating conditions where Candida thrives. Sitting in a wet swimsuit for extended periods does the same thing. Cotton underwear and changing out of damp clothing promptly reduce this risk.
Sexual activity doesn’t cause yeast infections in the way a sexually transmitted infection spreads, but friction and the introduction of saliva, lubricants, or a partner’s natural chemistry can alter your vaginal environment enough to trigger one. Using condoms can reduce this effect.
How to Tell It’s a Yeast Infection
Yeast infections produce a thick, white, odorless discharge, often described as resembling cottage cheese. You may also notice a white coating in and around the vagina, along with intense itching, redness, and burning during urination or sex. This is different from bacterial vaginosis, which causes a thinner, grayish, foamy discharge with a noticeable fishy smell. The distinction matters because the two conditions require completely different treatments, and self-treating for the wrong one can make things worse.
Reducing Your Risk
Prevention comes down to protecting the bacterial ecosystem that naturally suppresses Candida. Skip the scented products and douches entirely. Wear breathable cotton underwear and change out of wet or sweaty clothing quickly. Clean menstrual cups, diaphragms, and similar devices thoroughly after each use. If you’re prone to infections after antibiotics, ask your provider about preventive options before you start a course. For women with diabetes, keeping blood sugar well managed is one of the most effective ways to reduce recurrent infections.