Yeast infections happen when a fungus called Candida, which normally lives in small amounts in and on your body, grows out of control. About 75% of women will get at least one vaginal yeast infection in their lifetime, and 40% to 45% will get two or more. The triggers range from hormonal shifts and antibiotics to everyday habits like the underwear you choose.
What Happens Inside Your Body
Candida lives harmlessly in the vagina alongside protective bacteria, primarily lactobacillus, which keep the fungus in check by maintaining an acidic environment. When something disrupts that balance, Candida shifts from a passive, rounded yeast form into an aggressive, thread-like form that can physically penetrate the cells lining the vaginal wall. This shape change is the key moment: the elongated threads anchor themselves to the tissue, release enzymes that damage cells, and trigger an intense inflammatory response. That inflammation is what produces the itching, swelling, and discharge you feel.
Once Candida starts growing in its thread-like form, it can also create a biofilm, a thin, sticky layer that helps it cling to tissue and resist your body’s immune defenses. This is one reason yeast infections sometimes persist or come back quickly after treatment.
Antibiotics Are the Most Common Trigger
Antibiotics kill bacteria, but they don’t distinguish between harmful bacteria and the protective lactobacillus in your vagina. When those beneficial bacteria are wiped out, the acidic environment that keeps Candida dormant weakens, and the fungus multiplies. This is why yeast infections frequently show up during or shortly after a course of antibiotics for something completely unrelated, like a sinus infection or urinary tract infection.
Hormones and Estrogen
High estrogen levels create a more hospitable environment for Candida. Estrogen increases glycogen (a type of sugar stored in vaginal tissue), which feeds the fungus and promotes its shift into the invasive, thread-like form. This explains why yeast infections are more common during pregnancy, in the second half of the menstrual cycle when estrogen peaks, and in people using hormonal contraceptives or hormone replacement therapy. Postmenopausal women with low estrogen levels, by contrast, get yeast infections far less often.
Blood Sugar and Diabetes
Yeast feeds on sugar. When blood sugar runs high, excess glucose can show up in vaginal secretions and urine, essentially giving Candida a steady food supply. People with poorly controlled type 1 or type 2 diabetes are significantly more likely to develop recurrent yeast infections. Getting blood sugar under better control often reduces the frequency of infections on its own.
Clothing and Moisture
Candida thrives in warm, moist environments. Tight clothing and synthetic fabrics trap heat and sweat against the skin, creating ideal conditions for overgrowth. Cotton underwear is the best choice because it wicks moisture and allows airflow. A small cotton panel sewn into synthetic underwear doesn’t fully protect you, since the surrounding fabric still traps moisture.
A few practical habits that reduce risk:
- Change out of wet swimsuits and sweaty workout clothes as soon as possible.
- Sleep without underwear or in loose-fitting shorts or pajamas to increase airflow, especially if you’re already dealing with irritation.
- Skip panty liners for daily use, as they decrease breathability and can cause irritation.
Douching and Scented Products
The vagina is self-cleaning. Douching, which involves flushing the inside of the vagina with water mixed with vinegar, baking soda, or iodine, strips away protective bacteria and disrupts the natural acidity that keeps Candida in check. This can directly cause yeast overgrowth. Scented tampons, pads, powders, and sprays carry similar risks because the chemical fragrances can irritate vaginal tissue and alter the microbial balance. Warm water on the outside of the vulva is all you need. If you prefer soap, stick to a mild, unscented one.
Can You Get It From Sex?
Yes, yeast infections can pass between sexual partners, most commonly from someone with a penis to someone with a vagina during vaginal sex, or between two people with vaginas during genital-to-genital contact. That said, yeast infections are not classified as sexually transmitted infections because they frequently develop without any sexual contact at all. You don’t need to be sexually active to get one, and having one doesn’t mean your partner gave it to you.
Other Risk Factors
A weakened immune system, whether from conditions like HIV, from medications that suppress immunity, or from high-dose corticosteroids, makes it harder for your body to keep Candida in check. Chronic stress and sleep deprivation can also subtly weaken immune function enough to tip the balance. Some people simply seem more prone to yeast infections due to individual differences in their vaginal microbiome. A vagina dominated by certain strains of bacteria, particularly one called Lactobacillus iners, tends to create a more inflammatory environment that actually encourages Candida to shift into its invasive form.
How to Tell It’s a Yeast Infection
The hallmark symptoms are intense itching and irritation around the vulva and vaginal opening, along with a thick, white, odorless discharge that’s often compared to cottage cheese. You may also notice redness, swelling, and a burning sensation during urination or sex. The key distinction from bacterial vaginosis, the other common vaginal infection, is the smell: BV typically produces a thin, grayish, fishy-smelling discharge, while yeast infection discharge has no strong odor. If you’re unsure which you’re dealing with, the two require different treatments, so getting the right diagnosis matters.
Why Some People Get Them Repeatedly
If you’re getting four or more yeast infections a year, that pattern is considered recurrent. Recurrent infections often trace back to one of the risk factors above, particularly ongoing antibiotic use, uncontrolled blood sugar, or high estrogen levels. But in some cases, the Candida strain involved is one that’s naturally more resistant to standard antifungal treatments, or the fungus has formed a persistent biofilm that keeps reseeding the infection. Identifying and addressing the underlying trigger is usually more effective than treating each episode individually.