References UK clinical guidance from the NHS, the British HIV Association (BHIVA), and the British Association for Sexual Health and HIV (BASHH). Last updated: April 2026.
Trichomonal vaginitis is inflammation of the vagina caused by the parasitic STI trichomoniasis (Trichomonas vaginalis). It causes a distinctive frothy yellow-green discharge, itching and discomfort in many women. It’s treatable with a short course of antibiotics, but because up to half of women with trichomoniasis have no symptoms, many cases go undiagnosed.
Here’s what to know.
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What Causes It?
Trichomoniasis is caused by a tiny parasite called Trichomonas vaginalis. It’s transmitted through unprotected vaginal sex and occasionally through shared sex toys. It’s one of the most common curable STIs worldwide.
Typical Symptoms
- Frothy yellow-green vaginal discharge
- Unpleasant fishy or musty smell
- Itching and irritation
- Pain during sex
- Burning on urination
- Redness and swelling of the vulva
- Often no symptoms at all
Symptoms in Men
Men are often asymptomatic but can experience:
- Mild urethral discharge
- Burning on urination
- Itching or irritation
Diagnosis
| Test | Details |
|---|---|
| NAAT | Most sensitive; urine or swab |
| Microscopy | Direct identification of the parasite |
| Culture | Less commonly used now |
Treatment
- Metronidazole 400-500mg twice daily for 5-7 days, or a single 2g dose
- Avoid alcohol during and for 48 hours after metronidazole (severe reaction possible)
- Partners should be tested and treated simultaneously to prevent reinfection
- Safe to use during pregnancy
Complications If Untreated
- Persistent vaginitis and discomfort
- Increased risk of HIV acquisition
- Preterm birth and low birth weight in pregnancy
- Possible pelvic inflammatory disease
- Ongoing transmission to partners
Prevention
- Use condoms
- Get regular STI screening
- Treat partners at the same time
- Avoid sharing sex toys without barriers
When to Seek Help
- Any unusual vaginal discharge with smell
- Pain during sex
- Genital itching or burning
- Pelvic discomfort
- Recent new sexual partner
Read more: What is trichomoniasis? | Untreated trichomoniasis | Trichomoniasis vs chlamydia
Frequently Asked Questions
Is trichomonal vaginitis always from an STI?
Yes. The cause is the sexually transmitted parasite Trichomonas vaginalis.
Can it come back?
Yes, through reinfection from untreated partners. Treating both partners simultaneously prevents this.
Is it dangerous?
Usually not, but it causes discomfort, raises HIV risk and can cause pregnancy complications. Treatment is quick and effective.
Related reading
- What Is a Female (Internal) Condom?
- What Is Bacterial Vaginosis (BV)?
- Can You Test for STIs While on Your Period?
- Does a Vaginal Yeast Infection Smell?
- How Different STIs Affect Vaginal Discharge
Sources
- NHS — Sexual health conditions
- BASHH — UK clinical guidelines for STI management
- British HIV Association (BHIVA) — HIV treatment guidelines
- Terrence Higgins Trust — sexual health information
- UK Health Security Agency — STI surveillance data
Steve Page is a recognised expert on Sexually Transmitted Diseases (STDs) and STD treatments, having published numerous articles in peer-reviewed journals and presented his research at conferences around the world. He has an in-depth understanding of the latest medical research on STDs, and is an advocate for the development of new treatments and protocols to improve the health of those affected. In addition to his research, he has dedicated his career to understanding the causes and symptoms of STDs, as well as how to best treat those impacted.
