Trichomoniasis spreads through sexual contact, most commonly during vaginal sex without a condom with someone who is already infected. The parasite passes from a penis to a vagina, from a vagina to a penis, or from one vagina to another. What makes trich especially easy to catch is that 70% to 85% of infected people have minimal or no symptoms, meaning your partner may not know they’re carrying it.
The Main Way Trich Spreads
Trichomoniasis is caused by a single-celled parasite called Trichomonas vaginalis. Unlike bacteria or viruses, this is a tiny living organism that thrives in the urogenital tract. It passes between partners during unprotected penile-vaginal sex or through shared vaginal fluids between female partners.
The parasite does not commonly infect the mouth, throat, or anus. A large study from the Netherlands tested thousands of patients at all three body sites and found that throat and rectal infections were extremely rare, with positivity rates of just 0.1% and 0.2% respectively, compared to 0.5% for urogenital infections. The researchers concluded that testing outside the genital area isn’t warranted because the rates are so low. In practical terms, trich is a genital infection spread through genital contact.
Why You Can Get It Without Knowing
The biggest reason trich spreads so easily is that most people who have it don’t realize it. Between 70% and 85% of infected individuals show minimal or no symptoms, and without treatment, the infection can persist for months or even years. During that entire time, the parasite can pass to sexual partners.
When symptoms do appear, they typically show up 5 to 28 days after exposure. In women, symptoms can include unusual vaginal discharge, itching, burning, or discomfort during urination or sex. In men, symptoms are even less common, but can include irritation inside the penis or mild discharge. Because men so rarely have noticeable symptoms, they often unknowingly pass the infection to partners.
Can You Get Trich From a Toilet Seat or Towel?
This is one of the most common questions about trichomoniasis, and the answer is more nuanced than a flat “no.” Lab studies have shown that the parasite can survive outside the body for surprisingly long periods. After one hour on surfaces, live parasites were detected in 89% to 100% of samples depending on the surface type. On non-absorbent surfaces like plastic, one strain remained viable for up to 24 hours.
That said, surviving on a surface in a lab and actually causing an infection are different things. The parasite would need to transfer from a surface to the genital tract in sufficient numbers, which is an unlikely chain of events in everyday life. Sexual contact remains the overwhelmingly dominant route of transmission. Still, these survival findings do leave a small theoretical window for non-sexual transmission through shared damp towels or washcloths, which some researchers have noted as a possible explanation for rare cases in people who report no sexual exposure.
How the Parasite Takes Hold
Once the parasite reaches the genital tract, it uses specialized surface proteins to latch onto the cells lining the urogenital tissue. Some strains are significantly better at this than others. More adhesive strains release tiny packets (called extracellular vesicles) that can actually boost the sticking ability of nearby parasites, making the whole population more infectious. One adhesion-related protein, when overproduced in lab experiments, increased the parasite’s ability to bind to host cells by roughly 11-fold. This helps explain why some exposures lead to infection while others don’t: the strain matters.
What Raises Your Risk
The single biggest risk factor is having unprotected vaginal sex with someone whose infection status you don’t know. Beyond that, a few factors increase vulnerability:
- Multiple sexual partners: More partners means more chances of encountering someone who carries the parasite without symptoms.
- Not using condoms: Condoms provide a significant barrier. Studies have shown that consistent condom use reduces the risk of trich along with other STIs, though no study has pinpointed an exact percentage of protection for trichomoniasis alone.
- Having another STI: Trich can make you more susceptible to other infections and vice versa. The inflammation it causes can compromise the protective lining of the genital tract.
- A previous trich infection: Having been treated successfully in the past does not give you immunity. You can be reinfected immediately.
How Condoms and Testing Help
Condoms are the most practical prevention tool. While research on their effectiveness specifically against trich has produced mixed results across different populations, studies in younger women have shown that using condoms for 100% of sex acts significantly reduced the combined incidence of trich and other common STIs. Condoms won’t eliminate the risk entirely, especially since the parasite can potentially contact skin areas not covered by a condom, but they substantially lower it.
Because so many infections are silent, testing is the other critical tool. If you’re sexually active and concerned about exposure, a simple test can detect the parasite. The most sensitive lab method takes 3 to 7 days for results, but faster options exist including nucleic acid tests that many clinics now use as their standard. If you’ve had a new sexual partner or unprotected sex, getting tested is the only reliable way to know your status, since waiting for symptoms means you’ll miss the majority of infections that never produce any.
If you test positive, your current sexual partner needs treatment too. Otherwise, you’ll pass the infection back and forth. Both partners should be treated at the same time and avoid sex until treatment is complete and symptoms (if any) have resolved.