Yeast infections happen when a fungus called Candida, which normally lives in small amounts in the vagina, grows out of control. An estimated 75% of women will have at least one yeast infection in their lifetime, and 40% to 45% will have two or more. The trigger is almost always something that disrupted the environment keeping that fungus in check.
Your Vaginal Bacteria Keep Yeast in Check
A healthy vagina is home to beneficial bacteria, primarily Lactobacillus, that produce lactic acid and maintain an acidic environment. That acidity is what prevents Candida from multiplying. When something reduces those bacteria or shifts the pH, Candida takes the opportunity to overgrow.
Not all Lactobacillus species offer the same protection. Research published in the American Journal of Obstetrics and Gynecology found that women whose vaginal bacteria were dominated by one particular species, L. crispatus, were significantly less likely to harbor Candida than women dominated by L. iners, a less protective species that tends to colonize after the vaginal environment has already been disturbed. L. crispatus produces more lactic acid, which directly inhibits yeast growth. You can’t control which species you have, but understanding this helps explain why some women seem more prone to infections than others even when they’re doing everything “right.”
Antibiotics Are One of the Most Common Triggers
If your yeast infection showed up during or shortly after a course of antibiotics, that’s likely the cause. Antibiotics kill bacteria indiscriminately, wiping out the protective Lactobacillus along with whatever infection they were prescribed for. A study of over 1,500 women found that those who used antibiotics in the previous month were 75% more likely to develop a yeast infection compared to those who hadn’t taken any. The longer the antibiotic course, the higher the risk. Women with a history of past yeast infections were especially vulnerable to recurrence after antibiotics.
This doesn’t mean you should skip a prescribed antibiotic. But if you know you’re prone to yeast infections, it’s worth having a plan in place with your provider before starting one.
Hormonal Changes Play a Bigger Role Than You’d Think
Estrogen directly affects how well Candida can attach to vaginal tissue. High estrogen levels change the cell lining of the vagina in ways that make it more hospitable to yeast. Candida cells even have receptors for estrogen, which helps the fungus shift into a more aggressive growth form.
This is why yeast infections are more common during pregnancy, in the second half of the menstrual cycle (when estrogen peaks), and in women taking hormonal contraceptives with higher estrogen doses. If you notice a pattern of infections around the same point in your cycle, hormonal fluctuation is a likely explanation.
High Blood Sugar Feeds the Fungus
When blood sugar runs high, excess glucose shows up in vaginal secretions and urine, essentially feeding Candida. Women with diabetes have a notably higher risk of yeast infections, particularly when their blood sugar is poorly controlled. But you don’t need a diabetes diagnosis for this to matter. Periods of consistently high sugar intake or insulin resistance can create a similar effect on a smaller scale.
If you’re getting recurrent yeast infections and don’t have an obvious cause, it’s worth checking your blood sugar levels. Undiagnosed or early-stage diabetes sometimes shows up as repeated vaginal infections before other symptoms appear.
Products That Disrupt Your Vaginal Environment
Douching is one of the most well-documented risk factors. It strips away normal bacteria, shifts vaginal pH, and directly causes the kind of microbial imbalance that lets yeast flourish. The Office on Women’s Health notes that douching can cause overgrowth of harmful organisms and lead to yeast infections or bacterial vaginosis. Women who douche weekly are five times more likely to develop bacterial vaginosis than those who don’t.
Scented soaps, bubble baths, vaginal deodorants, and scented tampons or pads can have a similar, if milder, effect. The vagina is self-cleaning. Warm water on the external area is all that’s needed.
Clothing, Moisture, and Warmth
Candida thrives in warm, moist environments. Tight synthetic underwear and leggings trap heat and moisture against the skin, creating ideal conditions for fungal growth. Cotton underwear wicks away sweat and moisture far more effectively. Cleveland Clinic notes that even synthetic underwear with a cotton crotch panel doesn’t fully protect you, since the surrounding synthetic fabric still limits airflow.
Sitting in a wet swimsuit or sweaty workout clothes for extended periods is a classic setup for a yeast infection. Changing promptly after swimming or exercise makes a real difference. Going without underwear at night, or wearing loose pajamas, increases airflow and can help prevent infections or speed healing during one.
Immune Suppression and Medications
Your immune system normally keeps Candida populations small. Anything that weakens immune function raises your risk. Corticosteroids (often prescribed for asthma, autoimmune conditions, or inflammation), chemotherapy, and conditions like HIV all reduce the body’s ability to control fungal growth. Even significant stress or sleep deprivation can temporarily lower immune defenses enough to tip the balance.
Reducing Your Risk of Recurrence
If you’ve had one yeast infection, you already know how uncomfortable they are. A few practical changes lower the odds of another one:
- Wear 100% cotton underwear and change out of damp clothing quickly.
- Skip douching and scented products in the vaginal area entirely.
- Ask about prevention if you’re prescribed antibiotics and have a history of yeast infections.
- Monitor blood sugar if infections keep coming back without a clear trigger.
Probiotics are a popular option, and there’s some evidence they help. A pooled analysis of three clinical trials found that adding probiotics to standard antifungal treatment reduced one-month relapse rates by about 66%. One trial tracked women for six months and found recurrence dropped from 100% in the control group to 29% in women taking a Lactobacillus-based probiotic. However, other trials have found no significant benefit, and the overall evidence quality is mixed. If you’re dealing with recurrent infections (three or more per year, which affects fewer than 5% of women), probiotics may be worth trying alongside standard treatment rather than as a replacement.
Most yeast infections come down to one or more of these triggers creating an opening for a fungus that was already there. Identifying which factor applies to you is the most useful step toward keeping it from happening again.