Trichomoniasis: the common, curable STI behind the discharge
Last updated September 3, 2026.
Trichomoniasis (the trich) is the common sexually transmitted infection caused by the microscopic parasite: the frothy yellow-green discharge, the itching, and the soreness in women, and usually no symptoms at all in men. It is the commonest curable STI (millions of US cases yearly), most of the infected have no symptoms, and it is cured with the short antibiotic course: the partners treated together, or the ping-pong re-infection follows.
What are the symptoms?
In the women (when they come, the 5-to-28 days after): the increased discharge (the thin, the frothy, the yellow-green, the fishy-smelling), the itching and the soreness of the vulva-and-vagina, the burning on the urination, and the discomfort during the sex. In the men: usually nothing, occasionally the mild discharge or the burning after the urination. About 7-in-10 of the infected have no symptoms at all, which is why it circulates so widely.
Why does it matter if it is mild?
The three reasons the mild infection deserves the treatment: it inflames the genital tract in the way that increases the HIV acquisition-and-transmission risk, in the pregnancy it links to the early delivery and the low birth weight (the treated kind is the protected kind), and the untreated infection persists for the months-to-years (it does not burn out on its own). It is not dangerous in the dramatic sense, but it is not the nothing-to-do either.
How is it tested and treated?
- The test: the vaginal swab (the self-taken kind at many clinics) or the urine test, the results in the days; the full STI screen usually done together.
- The treatment: the metronidazole or the tinidazole (the single large dose or the week course): the cure in the great majority, with the no-alcohol-during-and-48-hours-after rule (the reaction is the severe flushing-and-vomiting).
- The partners treated together: the current partners get the medication without the waiting for their own test (the expedited approach), and the no-sex until everyone has finished.
- The re-test: recommended at the 3 months (the re-infection is common: about 1-in-5 within the months when the partners go untreated).
When does it need the prompt care?
The prompt (the days) testing for the discharge, the irritation, or the exposure. The pregnancy with the discharge gets the prompt review (the treatment is safe and the early treatment protects the pregnancy), and the severe pelvic pain with the fever is the same-day (the different problem: the pelvic inflammatory disease). Pymander's escalation routing is built and tested specifically for this class of decision; see the safety architecture working paper.
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Common questions
How is it different from a yeast infection or BV?
The overlap is real (all three bring the discharge and the irritation), and the differences are the tendencies, not the proofs: the yeast is the thick white cottage-cheese discharge with the intense itch (the little odor), the BV is the thin gray discharge with the fishy smell (the little itch), and the trich is the thin yellow-green frothy discharge with the smell and the soreness. The lab test settles it definitively, which is why the guessing-and-self-treating so often treats the wrong one.
My partner has no symptoms. Does he need treating?
Yes, always: the men rarely show the symptoms but carry and transmit the parasite, and the treating-only-you is the classic setup for the ping-pong re-infection (the about-1-in-5 re-infection rate within the months is mostly the untreated partners). The current partners get the medication alongside you (without even waiting for their own test), and the no-sex until everyone has finished the course.
Why no alcohol with the treatment?
The metronidazole-and-tinidazole block the alcohol metabolism (the acetaldehyde builds up: the severe flushing, the pounding heart, the vomiting), so the rule is the no alcohol during the course and for the 48-to-72 hours after (the tinidazole the 72). It is the few days: plan the course around the weekend plans, not the reverse.
Can I get it from a hot tub or a toilet seat?
No: the trichomoniasis is the sexually transmitted (the genital contact), and the parasite does not survive on the surfaces the way the myth suggests (the toilet seats, the hot tubs, the towels are not the transmission routes). The exception worth knowing: the shared unwashed sex toys can transmit (the wash-or-condom rule there).
I am pregnant. Is it safe to treat?
Yes, and the treating matters: the metronidazole is considered safe in the pregnancy, and the untreated trichomoniasis in the pregnancy links to the early delivery and the low birth weight. Tell the clinic you are pregnant (the regimen and the timing get chosen accordingly), and the treatment is the protection for the pregnancy, not the risk to it.
Will it go away on its own?
Reliably not: the untreated trichomoniasis persists for the months-to-years (the parasite keeps replicating, the symptoms wax and wane but the infection holds), and meanwhile it transmits and keeps the HIV-risk-raising inflammation going. The antibiotic course is short, cheap, and curative: there is no waiting-it-out version of this one.