Yeast infections happen when a fungus called Candida, which naturally lives in the vagina in small amounts, grows out of control. About 75% of women will get at least one vaginal yeast infection in their lifetime. The triggers range from hormonal shifts and antibiotics to everyday habits like wearing tight clothing. Understanding what disrupts the vaginal environment helps explain why these infections are so common.
What Happens Inside the Body
Your vagina normally hosts a balanced community of bacteria and yeast. Lactobacillus bacteria dominate this environment, keeping the vaginal pH between 3.8 and 4.5. At this acidity level, Candida exists in small numbers without causing problems. When something disrupts that bacterial balance, Candida can shift from a harmless, round yeast form into an aggressive, thread-like form that burrows into vaginal tissue and triggers inflammation.
Interestingly, yeast infections don’t raise vaginal pH the way bacterial infections do. The pH typically stays below 4.5 during a Candida infection. In fact, research suggests that lower pH levels can actually provoke a stress response in Candida, causing it to become more aggressive. This is one reason yeast infections can develop even when your vaginal chemistry seems otherwise normal.
Antibiotics Are the Most Common Trigger
Antibiotics kill bacteria, and they don’t distinguish between harmful bacteria and the protective Lactobacillus in your vagina. When you take antibiotics for a sinus infection, UTI, or any other illness, the resulting drop in beneficial bacteria gives Candida room to multiply unchecked. This is the single most well-documented trigger for vaginal yeast infections, and it can happen with both short and long courses of antibiotics.
Hormonal Changes That Shift the Balance
Estrogen plays a direct role in Candida growth. Higher estrogen levels increase the amount of glycogen (a sugar) stored in vaginal cells, which feeds yeast. This is why yeast infections are more common during pregnancy, in the second half of the menstrual cycle, and among women using hormonal birth control with higher estrogen doses.
The hormonal link also explains why yeast infections are rare before puberty and become less frequent after menopause, when estrogen levels drop significantly. If you notice infections clustering around certain points in your cycle, the hormonal connection is likely a factor.
Blood Sugar and Diabetes
Poorly controlled blood sugar creates an environment where yeast thrives. When blood glucose runs high, the body releases excess sugar through urine and vaginal secretions, essentially feeding Candida. Women with uncontrolled type 1 or type 2 diabetes are significantly more likely to develop recurrent yeast infections. Getting blood sugar under consistent control often reduces the frequency of infections.
Clothing, Moisture, and Everyday Habits
Candida grows best in warm, moist environments. Several everyday habits can create exactly those conditions:
- Tight, synthetic clothing. Non-breathable fabrics trap heat and moisture against the vulva. The CDC specifically recommends wearing cotton underwear and breathable, loose-fitting clothing to reduce risk.
- Sitting in wet clothes. Staying in a wet swimsuit or sweaty workout gear for hours keeps the area damp, which encourages yeast overgrowth.
- Douching and scented products. Douching washes away protective bacteria. Scented soaps, sprays, and bubble baths can irritate vaginal tissue and alter the microbial balance. Keeping the area clean with plain water is sufficient.
A Weakened Immune System
Your immune system normally keeps Candida populations in check. Anything that suppresses immune function, from HIV to chemotherapy to long-term corticosteroid use, raises the risk of yeast overgrowth. Chronic stress and sleep deprivation can also weaken immune defenses enough to tip the balance, though these factors are harder to quantify.
Sex Can Play a Role, but It’s Not an STI
Yeast infections are not sexually transmitted infections. You can get one without ever having sex. That said, sexual activity can contribute. Oral sex, vaginal sex, and anal sex can all introduce or redistribute yeast between partners. About 15% of male partners develop an itchy rash on the penis after unprotected sex with a woman who has an active yeast infection.
If you have a male partner, his risk of infection is low, and routine treatment of partners isn’t typically necessary. Condoms and dental dams can reduce the chance of passing yeast back and forth. If you notice that infections keep returning after sex, it’s worth considering whether reinfection from a partner could be a factor.
What a Yeast Infection Feels Like
The hallmark symptoms are intense itching and irritation of the vulva and vagina. Most women also notice a thick, white discharge that looks like cottage cheese and typically has no strong odor (a key difference from bacterial vaginosis, which produces a fishy smell). Other common symptoms include soreness, burning during urination, and pain during sex. The vulva may appear swollen, red, or cracked in more severe cases.
Why Some Women Get Them Repeatedly
Between 5% and 10% of women develop recurrent yeast infections, defined as four or more episodes in a single year. Recurrence doesn’t mean you’re doing something wrong. Some women are genetically more susceptible because of differences in how their immune system responds to Candida. Others have persistent triggers they can’t easily avoid, like a medication they need to stay on or a hormonal pattern tied to their cycle.
Recurrent infections sometimes involve Candida species other than the most common one, which can be more resistant to standard over-the-counter treatments. If you’re dealing with frequent infections, getting a lab culture rather than relying on self-diagnosis helps identify whether a resistant strain is involved and guides more effective treatment.