Yeast infections happen when a fungus called Candida, which normally lives in small amounts in the vagina, grows out of control. This isn’t caused by poor hygiene or sexual contact. It’s an internal imbalance, and roughly three out of four women will experience at least one yeast infection in their lifetime. Understanding what tips that balance helps explain why they happen and how to reduce the risk.
What Keeps Yeast in Check
A healthy vagina maintains an acidic environment populated by beneficial bacteria, particularly a species called Lactobacillus. These bacteria produce lactic acid, which suppresses Candida growth and keeps the fungal population small. When something disrupts this bacterial community or changes the vaginal environment, Candida can multiply rapidly and cause symptoms.
Not all protective bacteria are equally effective. Research published in the American Journal of Obstetrics and Gynecology found that women whose vaginal bacteria were dominated by one particular Lactobacillus strain were nearly three times more likely to harbor Candida compared to women with a different, more acid-producing strain. This helps explain why some women seem more prone to yeast infections than others, even without an obvious trigger.
How Hormones Fuel Yeast Growth
Estrogen plays a direct role. It stimulates the cells lining the vagina to produce glycogen, a sugar-like molecule that Candida albicans (the most common species behind yeast infections) uses as food. During times of higher estrogen, free glycogen in the vagina can reach levels roughly ten times higher than glucose, creating an environment where yeast thrives.
This is why yeast infections cluster around specific life stages and hormonal shifts:
- Puberty: Rising estrogen levels create a new vaginal environment that Candida can exploit, making yeast infections possible for the first time.
- The menstrual cycle: Estrogen peaks around ovulation, which is why some women notice recurring infections mid-cycle.
- Pregnancy: Sustained high estrogen levels make yeast infections significantly more common during pregnancy.
- Hormonal birth control: Methods containing estrogen can raise glycogen production and shift the balance toward yeast overgrowth.
Before puberty, yeast infections are less common precisely because estrogen levels are low. When they do occur in younger girls, the triggers are usually external irritants or antibiotics rather than hormonal shifts.
Antibiotics Are a Major Trigger
Taking antibiotics is one of the most well-documented causes of yeast infections. Antibiotics kill bacteria indiscriminately, wiping out the protective Lactobacillus along with whatever infection they’re treating. With less lactic acid being produced, the vaginal pH rises and Candida can multiply freely.
A study in the American Journal of Obstetrics and Gynecology found that women who used antibiotics in the month before a clinic visit had 75% higher odds of developing a symptomatic yeast infection compared to women who hadn’t taken antibiotics. The type of antibiotic didn’t matter. Broad-spectrum and narrow-spectrum antibiotics carried similar risk. This is why yeast infections so often show up a few days into or just after finishing a course of antibiotics for something completely unrelated, like a sinus infection or urinary tract infection.
High Blood Sugar and Immune Changes
Poorly controlled diabetes creates a particularly hospitable environment for yeast. When blood sugar runs high, excess sugar can appear in vaginal secretions and urine, essentially feeding Candida directly. Women and girls with uncontrolled diabetes are more likely to experience yeast infections, and these infections can be harder to clear until blood sugar is better managed.
Any condition or medication that weakens the immune system can also open the door. Corticosteroids, chemotherapy, and conditions like HIV reduce the body’s ability to keep Candida populations in check. Even everyday factors like significant stress or lack of sleep can temporarily suppress immune function enough to allow overgrowth in someone already prone to infections.
Moisture, Clothing, and Irritants
Yeast thrives in warm, moist environments. Wearing underwear made from synthetic materials like nylon traps heat and sweat against the skin, creating conditions that encourage Candida growth. Cotton underwear wicks moisture away and allows airflow, which is why it’s consistently recommended for prevention. Tight clothing, wet swimsuits left on too long, and exercise clothes worn for extended periods all contribute to the same problem.
For younger girls, especially those still learning bathroom habits, wiping back to front can introduce intestinal yeast (Candida naturally lives in the gut) to the vaginal area. Bubble baths, scented soaps, and other chemical irritants can also disrupt the delicate skin and bacterial balance around the vulva, making infection more likely even before puberty.
Douching Disrupts the Natural Balance
Douching, or flushing the vagina with water or a cleansing solution, is one of the most counterproductive things you can do for vaginal health. It strips away the beneficial bacteria and alters the natural acidity that keeps infections at bay. The Office on Women’s Health states plainly that douching can cause an overgrowth of harmful organisms, leading directly to yeast infections or bacterial vaginosis. If an infection is already present, douching can push the organisms deeper into the reproductive tract. The vagina is self-cleaning, and no internal washing is needed.
Yeast Infections Are Not Sexually Transmitted
A yeast infection is not a sexually transmitted infection. You can get one without ever having had sex, which is why they occur in children, teenagers, and adults alike. Sexual activity can sometimes contribute to changes in vaginal bacteria or introduce minor irritation, but Candida overgrowth is fundamentally an internal process driven by the factors above. You don’t “catch” a yeast infection from another person the way you would chlamydia or gonorrhea.
Recognizing the Symptoms
The hallmark symptoms are intense itching and redness of the vulva and vaginal opening, often accompanied by a thick, white discharge that looks like cottage cheese. The discharge typically has no odor, which is one way to distinguish a yeast infection from bacterial vaginosis (thin, grayish discharge with a fishy smell) or trichomoniasis (gray-green discharge that may also smell). Burning during urination or during sex is also common.
If you’ve had a yeast infection before and recognize the symptoms, over-the-counter antifungal creams and suppositories are effective for uncomplicated cases. These treatments range from single-dose options to courses lasting up to a week. A single-dose oral antifungal pill is also available by prescription. For women who experience four or more yeast infections in a year, or who have diabetes or a weakened immune system, a longer or more tailored treatment approach is typically needed.
Reducing Your Risk
You can’t eliminate the possibility of yeast infections entirely, but you can reduce how often they happen. Wearing breathable cotton underwear, changing out of wet or sweaty clothes promptly, and avoiding scented products in the vaginal area all help maintain a stable environment. Skipping douching entirely removes one of the biggest controllable risk factors. If you notice a pattern of yeast infections following antibiotic use, that’s worth mentioning to your healthcare provider, as preventive steps can sometimes be taken alongside antibiotic treatment.
For girls going through puberty, knowing that occasional yeast infections are a normal (if annoying) consequence of hormonal changes can be reassuring. The same basic prevention strategies apply at every age: keep the area dry, avoid irritating products, and let the body’s natural defenses do their job.