Women get trichomoniasis through sexual contact with an infected partner. The infection is caused by a single-celled parasite called Trichomonas vaginalis, which passes between people during vaginal sex. It affects roughly 3.7 million people in the United States, with an estimated prevalence of 3.1% among women.
How the Parasite Spreads
Trichomoniasis spreads when the parasite moves from one person’s genitals to another’s during unprotected vaginal intercourse. The parasite travels in genital fluids and can pass from a penis to a vagina, from a vagina to a penis, or between two vaginas. Unlike some other sexually transmitted infections, trichomoniasis does not typically spread through oral or anal sex.
Once the parasite reaches the female genital tract, it colonizes the lower reproductive area: the vulva, vagina, cervix, or urethra. It attaches to the surface cells lining these tissues and feeds on them, which is what eventually triggers inflammation and symptoms. The incubation period, meaning the gap between exposure and the first signs of infection, ranges from 5 to 28 days.
Can You Get It Without Sex?
Non-sexual transmission is possible but extremely rare. The parasite is very sensitive to drying, though it can survive for several hours in body fluids or on moist objects like sponges and towels. In theory, sharing a damp towel or washcloth with an infected person could transfer the parasite, but this is not considered a meaningful route of infection in practice. The overwhelming majority of cases result from direct genital-to-genital contact.
Why Women Are More Vulnerable Than Men
Women are significantly more likely to carry trichomoniasis than men. National survey data from the CDC found that infection prevalence was 1.8% in women compared to just 0.5% in men. After adjusting for other factors, women had more than five times the odds of being infected compared to men. Part of this disparity is biological: the warm, moist environment of the vagina is an ideal habitat for the parasite, which allows it to establish itself more easily and persist longer than it does in the male urethra, where it is more often flushed out during urination.
Risk Factors That Increase Your Chances
Several factors raise the likelihood of getting trichomoniasis beyond simply having vaginal sex with an infected partner:
- Multiple sexual partners. More partners means more potential exposure to the parasite.
- Not using condoms. Consistent condom use reduces but does not completely eliminate risk, since the parasite can live on skin areas a condom doesn’t cover.
- Smoking. Active smokers had nearly nine times the odds of infection compared to people with no nicotine exposure in a large national survey. Smoking may impair the immune defenses of the vaginal lining.
- Lower income. People living below the federal poverty level had about seven times the odds of infection compared to those earning more than three times that threshold, likely reflecting differences in access to screening and treatment.
Many Women Have No Symptoms at All
A large portion of women with trichomoniasis never realize they’re infected. The infection can persist for months or even years without causing noticeable problems, which makes it easy to unknowingly pass to a partner. When symptoms do appear, they typically include a frothy, yellow-green vaginal discharge with a strong odor, itching or irritation around the vagina, and discomfort during urination or sex. These symptoms can come and go, which sometimes leads women to dismiss them as a yeast infection or bacterial vaginosis.
This high rate of silent infection is one reason trichomoniasis is so common. People who don’t know they’re infected don’t seek treatment and continue to transmit the parasite to new partners.
Reinfection Is Surprisingly Common
Getting treated once doesn’t protect you from getting trichomoniasis again. Reinfection rates are high enough that the CDC recommends all sexually active women get retested about three months after completing treatment, regardless of whether their partner was also treated. If that three-month window isn’t possible, retesting should happen at the next medical visit within 12 months.
Reinfection usually happens for one of two reasons: either a sexual partner wasn’t treated and passes the parasite right back, or a new partner carries the infection. Both partners need to be treated at the same time and should avoid sex until the treatment course is finished and symptoms have resolved. Without that coordination, the parasite simply bounces back and forth between partners.
How Testing Works
Trichomoniasis is diagnosed through a lab test on vaginal fluid. Your provider may collect a swab during a pelvic exam, or in some settings you can provide a self-collected swab. The most accurate tests use a method that detects the parasite’s genetic material, which catches infections that older microscope-based methods sometimes miss. Because so many cases are asymptomatic, testing is the only reliable way to know if you’re infected. If you’re sexually active and have a new partner, or if a partner has been diagnosed, requesting a test is straightforward and often covered by insurance or available at low-cost clinics.