A vaginal infection is an inflammation or imbalance in the vagina that causes symptoms like unusual discharge, itching, burning, or odor. The three most common types are bacterial vaginosis, yeast infections, and trichomoniasis. Together, these account for the vast majority of cases, though non-infectious causes like hormonal changes or chemical irritants make up another 5% to 10%.
How the Vagina Normally Protects Itself
A healthy vagina maintains a pH between 3.8 and 4.5, which is acidic enough to keep harmful microbes in check. This acidity comes from beneficial bacteria, primarily Lactobacillus species, that dominate the vaginal microbiome. These bacteria produce lactic acid and other compounds that create an environment hostile to pathogens. When something disrupts this balance, whether it’s antibiotics, hormonal shifts, sexual contact, or irritants, the door opens for an infection to take hold.
Bacterial Vaginosis
Bacterial vaginosis (BV) is the most common cause of vaginal symptoms, responsible for 40% to 50% of cases. It’s not technically an infection in the traditional sense. Instead, it’s a shift in the vaginal ecosystem: the population of protective Lactobacillus bacteria drops sharply, and anaerobic bacteria (organisms that thrive without oxygen) multiply by 100 to 1,000 times their normal levels.
The hallmark of BV is a clear, heavy discharge with a noticeable fishy smell. The odor is often stronger after sex. Unlike yeast infections, BV typically doesn’t cause significant itching or redness. Many people with BV have no symptoms at all, which is part of what makes it tricky. Left untreated, BV can increase the risk of other infections and cause complications during pregnancy.
BV is treated with prescription antibiotics, either taken orally or applied as a vaginal gel or cream. A typical course runs five to seven days. The problem is recurrence: BV comes back frequently. Early research into specially designed probiotics containing multiple strains of Lactobacillus crispatus has shown promise. In one study, two-thirds of participants who received these probiotics had protective bacteria colonizing their vaginas within five weeks, and those women were significantly less likely to experience BV again.
Yeast Infections
Yeast infections (vulvovaginal candidiasis) account for 20% to 25% of vaginal infection cases. They happen when Candida, a type of fungus that normally lives in the vagina in small numbers, multiplies beyond what the body can control.
The symptoms are distinct from BV. Yeast infections cause intense itching and irritation of the vagina and vulva, along with a thick, white, cottage cheese-like discharge that has little or no odor. You may also notice burning during urination or sex, redness, and swelling around the vaginal opening.
Several things can trigger an overgrowth:
- Antibiotics, which kill protective bacteria along with the targeted infection
- Pregnancy, due to shifting hormone levels
- Poorly managed diabetes, because elevated blood sugar feeds yeast growth
- A weakened immune system
- Hormonal birth control or hormone therapy that raises estrogen levels
Mild yeast infections often respond to over-the-counter antifungal creams or suppositories. More severe or recurring infections typically require a prescription antifungal. If you’ve never had a yeast infection before, it’s worth getting a diagnosis rather than self-treating, since the symptoms overlap with other conditions that need different treatment.
Trichomoniasis
Trichomoniasis is the only one of the three common vaginal infections that’s sexually transmitted. It’s caused by a tiny parasite called Trichomonas vaginalis, which passes between partners during genital contact, including vaginal, oral, or anal sex. It can spread from a penis to a vagina, from a vagina to a penis, or from one vagina to another.
The discharge from trichomoniasis is thin or frothy with a foul smell, and it can be clear, white, yellow, or green. Along with the discharge, you may experience genital burning, soreness, itching, pain during urination or sex, and lower abdominal discomfort. Men can carry and spread the parasite too, though their symptoms tend to be milder: irritation inside the penis, burning with urination, or a clear discharge.
Trichomoniasis is treated with prescription oral antibiotics, and both you and your sexual partner need treatment at the same time to prevent reinfection. Without treatment, the infection doesn’t resolve on its own and can be passed back and forth indefinitely.
Non-Infectious Causes
Not every vaginal irritation is caused by a microbe. Non-infectious vaginitis accounts for 5% to 10% of cases and can mimic the symptoms of an infection closely enough to cause confusion.
Atrophic vaginitis is one of the most common non-infectious types. It happens when estrogen levels drop, causing vaginal tissues to become thinner, drier, and more fragile. This occurs most often after menopause or during perimenopause, but it can also happen during breastfeeding, after surgical removal of the ovaries, during certain cancer treatments, or while taking medications that lower estrogen. Symptoms include vaginal dryness, burning, itching, a thin watery discharge, pain during sex, and more frequent urinary tract infections.
Irritant or allergic vaginitis is another possibility. Scented soaps, douches, laundry detergents, fabric softeners, spermicides, and even certain types of underwear fabric can trigger inflammation that looks and feels like an infection. If symptoms come and go with product use, an irritant is the likely culprit.
How to Tell Which Type You Have
The differences in discharge are the most useful clue. A thick, white, odorless discharge that looks like cottage cheese points toward a yeast infection. A thin, clear discharge with a fishy smell suggests BV. A frothy, foul-smelling discharge that’s yellow or green is more consistent with trichomoniasis. Itching is the dominant complaint with yeast infections, while odor is the standout feature of BV.
That said, these patterns aren’t always clear-cut, and it’s common for more than one type of infection to be present at the same time. A healthcare provider can usually distinguish between them with a simple in-office exam that involves checking the pH of your vaginal fluid and looking at a sample under a microscope. This takes just a few minutes and removes the guesswork.
Reducing Your Risk
Because vaginal infections are fundamentally about microbial balance, most prevention strategies focus on protecting the vaginal ecosystem. Avoid douching, which strips away protective bacteria and raises vaginal pH. Choose unscented soaps and detergents for anything that contacts the vulvar area. Wear breathable cotton underwear, and change out of wet swimsuits or sweaty workout clothes promptly. If you’re taking antibiotics for another condition, be aware that a yeast infection is a common side effect.
For trichomoniasis specifically, consistent condom use reduces transmission risk. For BV and yeast infections, the picture is more complex since these aren’t classic sexually transmitted infections, but new sexual partners and unprotected sex are associated with higher rates of BV.
Probiotic approaches are gaining traction for people who deal with recurrent BV. The goal is to reintroduce protective Lactobacillus bacteria that can recolonize the vagina and restore its natural defenses. While commercial probiotic supplements vary widely in quality and evidence, clinical research on targeted strains designed for vaginal health is showing encouraging early results.