Trichomoniasis spreads through sexual contact with an infected person. It is caused by a microscopic parasite called Trichomonas vaginalis, and it passes between partners during vaginal sex. With roughly 156 million new cases worldwide each year, it is one of the most common sexually transmitted infections, yet many people who carry it have no idea they’re infected.
How Trichomoniasis Spreads
The parasite travels in genital fluids and passes from one person to another during unprotected vaginal intercourse. In women, it infects the vagina, cervix, and urethra. In men, it typically lives inside the urethra or under the foreskin. Transmission happens when these tissues come into direct contact during sex.
Trichomoniasis is not typically spread through oral sex, anal sex, kissing, or casual contact like hugging or sharing food. While the parasite has been found alive on damp objects like wet towels and washcloths, fomites have not been proven to play any real role in spreading infection. The likelihood of catching it outside of sexual contact is extremely low.
Asymptomatic Carriers Are the Biggest Factor
What makes trichomoniasis so easy to contract is that most people who have it don’t know. The majority of infected men never develop symptoms. Among women, just over half notice vaginal discharge, and the rest can carry the parasite silently. Because there are no visible signs in many cases, the infection gets passed along by partners who genuinely believe they’re healthy.
Asymptomatic carriers are still contagious. The parasite lives in the genital tract whether or not it causes irritation, which means someone can transmit it during any unprotected sexual encounter. This is also why reinfection is so common: about 1 in 5 people who get treated for trichomoniasis pick it up again within three months, usually because their partner wasn’t treated at the same time.
What Raises Your Risk
Several factors increase the chance of contracting trichomoniasis:
- Unprotected vaginal sex. Condoms significantly reduce transmission, though they don’t eliminate risk entirely since the parasite can live on skin not covered by a condom.
- Multiple sexual partners. More partners means more potential exposure to someone carrying the parasite unknowingly.
- A partner who hasn’t been tested or treated. Because most carriers are asymptomatic, the infection circulates among people who assume they’re in the clear.
- A previous trichomoniasis infection. Having been infected once doesn’t create immunity. You can get it again immediately if exposed.
Symptoms When They Do Appear
When trichomoniasis does cause symptoms, they typically show up within 5 to 28 days of exposure, though some people don’t notice anything for much longer. Women may experience a frothy, yellow-green vaginal discharge with a strong odor, along with itching, burning, or soreness around the genitals. Pain during urination or sex is also common.
Men are far less likely to have symptoms, but some develop a mild discharge from the penis, irritation inside it, or a slight burning after urination or ejaculation. These symptoms can be easy to dismiss or mistake for something else, which contributes to the infection going undiagnosed.
How It Gets Diagnosed
Trichomoniasis won’t show up on a standard STI panel unless your provider specifically tests for it. The most accurate method is a nucleic acid amplification test, which detects the parasite’s genetic material with about 97% sensitivity. Older methods are less reliable. A traditional microscope exam of vaginal fluid catches only 51 to 66% of infections, meaning it misses roughly a third to half of cases. Rapid antigen tests and cultures fall somewhere in between, with sensitivity around 85 to 90%.
If you’re concerned about exposure, ask your provider specifically for a trichomoniasis test. It’s often left out of routine screenings, particularly for men, where testing options have historically been more limited.
Why Partner Treatment Matters
Trichomoniasis is curable with a single course of antiparasitic medication, but the treatment only works long-term if both you and your sexual partner are treated at the same time. Without concurrent treatment, the parasite simply passes back and forth. The CDC recommends retesting about three months after treatment regardless of whether you believe your partner was treated, precisely because reinfection rates are so high.
If your partner is untreated or you resume unprotected sex before both of you have completed treatment, you will very likely get reinfected. This ping-pong pattern is one of the main reasons trichomoniasis remains so widespread despite being easy to cure.