Pelvic pain or pregnancy changes the pathway
Seek same-day clinical assessment for lower abdominal or pelvic pain, fever, vomiting, pain during sex, bleeding between periods, pregnancy with new discharge or irritation, or rapidly worsening symptoms. Severe pain, fainting, shoulder-tip pain, or heavy bleeding with possible pregnancy can indicate ectopic pregnancy and requires emergency care. Vaginal odour alone is not an emergency, but it should not be used to rule out a more serious condition.
Bacterial vaginosis and trichomoniasis can both cause thin discharge and a fishy odour, but they are not the same. Bacterial vaginosis, or BV, is a shift in the balance of vaginal bacteria and is not classified as a conventional STI. Trichomoniasis is an STI caused by a parasite. Symptoms overlap, so examination and a validated vaginal test are more reliable than appearance, smell, or a home pH strip.
Key points
- Many people with BV or trichomoniasis have no symptoms.
- BV often causes thin white or grey discharge and odour with relatively little inflammation.
- Trichomoniasis can cause yellow-green or thin discharge, irritation, urinary burning, or pain during sex, but none is diagnostic.
- Sex partners must be treated for trichomoniasis; recurrent-BV partner guidance changed in 2025 and now supports discussion for selected couples.
- Recurrent symptoms need retesting because yeast, cervicitis, STIs, irritation, and hormonal change can look similar.
What bacterial vaginosis is
A healthy vagina contains a community of bacteria, often dominated by lactobacilli that produce acids. In BV, that balance shifts and a more diverse group of anaerobic bacteria becomes abundant. It is a dysbiosis rather than one invading pathogen.
BV is associated with a new or multiple sexual partners, lack of condom use, sex between people with vaginas, and douching, but it can occur without recent sexual activity. It is not proof of infidelity and does not result from being “unclean.” Excessive cleansing can make the imbalance worse.
Many cases are asymptomatic. When symptoms occur, thin white or grey discharge and a strong fish-like odour, often more noticeable after sex or during menstruation, are common. Mild burning or external itching can occur, but intense soreness should broaden the differential.
What trichomoniasis is
Trichomoniasis is caused by the protozoan parasite Trichomonas vaginalis. It spreads through sexual contact, most often penis-to-vagina or vagina-to-vagina. Mouth and rectal infection are uncommon. A person can transmit it without symptoms.
CDC says about 70% of infected people have no signs or symptoms. When present, symptoms in people with a vagina can include clear, white, yellowish, or greenish discharge, odour, redness, itching, soreness, burning with urination, or discomfort during sex. People with a penis may have urethral irritation, discharge, or burning after urination or ejaculation.
Untreated infection can persist for months or years. Genital inflammation can increase HIV acquisition or transmission risk. In pregnancy, trichomoniasis is associated with preterm birth and low birth weight, although individual risk and treatment decisions require maternity care.
Why symptoms cannot separate them
| Feature | BV | Trichomoniasis |
|---|---|---|
| Cause | Vaginal bacterial imbalance | Sexually transmitted parasite |
| Symptoms | Often none; thin discharge and odour | Often none; discharge, irritation, burning |
| Inflammation | Often limited | May cause marked redness or soreness |
| Vaginal pH | Often above 4.5 | Often above 4.5 |
| Partners | Selected recurrent cases now merit discussion | Current partners require treatment |
| Retesting | Return if symptoms recur | Women should be retested at about three months |
Discharge colour and odour overlap. Vaginal pH can rise with either condition, menstrual blood, semen, or other changes. A normal pH does not exclude every case of trichomoniasis. No home smell, microscope, or pH rule is accurate enough to select treatment safely.
Other common explanations
Vulvovaginal candidiasis often causes intense itching, soreness, and thick discharge but may have little discharge. Gonorrhea, chlamydia, and Mycoplasma genitalium can cause cervicitis with discharge or bleeding. Genital herpes can cause pain or burning before sores become visible.
Retained tampons, contact dermatitis from fragrance or detergent, lichen conditions, genitourinary syndrome of menopause, and a foreign body can change discharge or cause irritation. Pelvic pain or fever raises concern for pelvic inflammatory disease rather than uncomplicated vaginitis.
How clinicians test
The history covers discharge, odour, irritation, urinary and pelvic symptoms, pregnancy, menstruation, sexual exposure, products, douching, self-treatment, and recent antimicrobials. A clinician may examine the vulva, vagina, and cervix and collect a vaginal swab. Self-collected vaginal swabs are valid for many laboratory assays when the service provides them.
BV can be diagnosed using Amsel criteria: characteristic discharge, elevated pH, clue cells on microscopy, and an amine odour test. A Gram-stained vaginal smear scored for bacterial patterns is a laboratory reference method. Validated molecular tests can detect BV-associated bacteria and lactobacilli, usually in symptomatic people.
Trichomoniasis is best detected with a sensitive molecular test, or NAAT, where available. Wet-mount microscopy can show moving parasites but loses sensitivity quickly after collection, so a negative wet mount does not reliably exclude infection. Some rapid antigen tests and cultures are also used.
A broad vaginitis panel may test BV, trichomoniasis, and yeast, but not necessarily chlamydia or gonorrhea. Ask what organisms and specimen sites were included.
Treatment is different
Bacterial vaginosis
Symptomatic BV is treated with an oral or vaginal antibiotic regimen. Route, pregnancy, breastfeeding, allergies, interactions, and preference influence the choice. Treatment relieves symptoms and may reduce some STI and pregnancy risks, but recurrence is common.
Do not use leftover antibiotics, vaginal antiseptics, douches, fragranced washes, or intravaginal herbs. Over-the-counter yeast treatment will not correct BV and may delay diagnosis. Probiotics are marketed heavily, but CDC guidance does not support available products as a replacement or established adjunct to treatment.
Trichomoniasis
Trichomoniasis requires an effective oral prescription medicine; topical vaginal products do not reliably clear infection from all sites. Regimens differ by anatomy, HIV status, pregnancy, previous treatment, and national guideline. This page does not name a drug or dose.
Complete the treatment exactly as prescribed. Do not assume the infection is gone because odour or irritation improved. Persistent infection may reflect re-exposure, incomplete treatment, an incorrect diagnosis, or drug resistance and needs a clinician-led testing and treatment plan.
Partner care: an important difference and a recent change
For trichomoniasis, current sexual partners should receive treatment at the same time even when they have no symptoms. Avoid sex until everyone has completed treatment and symptoms have resolved. Expedited partner therapy is an option in some jurisdictions, but pregnancy, allergy, other STIs, and local law need consideration.
Older BV guidance, including the CDC 2021 guideline, did not recommend routine partner treatment based on earlier trials. Newer evidence changed the conversation. In October 2025, ACOG recommended considering concurrent oral and topical antimicrobial treatment for male partners of adults with recurrent symptomatic BV and shared decision-making for same-sex partners and first episodes.
This does not make BV a conventional STI or justify sharing medication. It means sexual exchange of BV-associated bacteria can matter for recurrence in some partnerships. The patient and partner should discuss current local guidance, allergies, pregnancy potential, relationship structure, and whether both can complete treatment together.
Follow-up and recurrence
BV often returns within months. Recurrent odour or discharge should be retested rather than repeatedly treated from memory. Clinician-led options include another recommended course, a different regimen, longer suppressive strategies, and now partner therapy in selected cases. The right pathway depends on confirmation and previous response.
CDC recommends that sexually active women treated for trichomoniasis be retested at about three months because reinfection is common, even when partners report treatment. Routine retesting evidence for men is insufficient. Testing very soon after treatment may detect residual nucleic acid, so follow the clinic’s timing.
People diagnosed with trichomoniasis should be offered testing for HIV, syphilis, gonorrhea, and chlamydia according to exposure and local guidance. A trichomoniasis diagnosis is not evidence about when infection occurred or who had it first; asymptomatic infection can persist.
Pregnancy
Contact prenatal care for new odour, discharge, bleeding, irritation, urinary symptoms, or pelvic pain. BV and trichomoniasis are associated with adverse pregnancy outcomes, and treatment choices must be pregnancy-appropriate. Do not insert boric acid or use a leftover vaginal product during pregnancy.
Screening people without symptoms differs by risk and country. Symptoms should be assessed; a home pH result is not a prenatal diagnosis.
Questions people often ask
Does BV mean my partner cheated?
No. BV is a microbiome imbalance and can recur or occur without a new exposure. A diagnosis cannot establish infidelity.
Can a fishy smell identify BV?
No. BV is common, but trichomoniasis and other conditions can also cause odour. Testing guides the different partner and follow-up pathways.
Should a partner be treated for BV?
For recurrent symptomatic BV, 2025 ACOG guidance supports considering concurrent partner treatment. Other guidelines may not yet reflect the new evidence, so use shared clinical decision-making.
Can trichomoniasis return after treatment?
Yes. Reinfection is common if a partner remains untreated, and treatment failure can occur. Retesting at about three months is recommended for women.
Sources and evidence scope
This guide was researched using 2025 WHO fact sheets on bacterial vaginosis and trichomoniasis, current CDC information on trichomoniasis and clinical guidance for BV and trichomoniasis, and the 2025 ACOG update on concurrent BV partner therapy plus its vaginitis guidance. Sources were checked on August 21, 2026. Tests, prescriptions, partner treatment, and retesting policies vary by country.