What are the causes of green vaginal discharge?

Causes of Green Vaginal Discharge

Green vaginal discharge is most characteristically caused by trichomoniasis, a sexually transmitted protozoal infection, though other conditions including bacterial vaginosis and aerobic vaginitis can occasionally present with greenish discharge. 1, 2

Primary Cause: Trichomoniasis

Trichomoniasis caused by Trichomonas vaginalis produces the classic presentation of frothy greenish discharge with prominent vulvar itching and irritation. 3, 2

• The CDC specifically identifies "diffuse, malodorous, yellow-green discharge with vulvar irritation" as the hallmark of trichomoniasis 3
• This is a sexually transmitted infection requiring treatment of both the patient and all sexual partners simultaneously to prevent reinfection 2
• The "strawberry cervix" (red punctate lesions) may be visible on speculum examination 3
• Vaginal pH is typically elevated above 4.5 1
• Wet mount microscopy reveals motile flagellated trichomonads, though this test misses 30-50% of cases 3

Secondary Causes

Bacterial Vaginosis (Atypical Presentation)

While bacterial vaginosis classically produces thin, white-gray discharge with fishy odor, it can occasionally appear greenish 1, 4:

• BV results from overgrowth of anaerobic bacteria including Gardnerella vaginalis, Prevotella species, and Mobiluncus species, replacing protective lactobacilli 1, 4
• Diagnosis requires 3 of 4 Amsel criteria: homogeneous discharge, clue cells on microscopy, pH >4.5, and positive whiff test 1
• Critically, BV lacks significant inflammation—the vagina does not appear red or inflamed 2
• This distinguishes it from trichomoniasis, which causes prominent vulvar inflammation 2

Aerobic Vaginitis

Aerobic vaginitis can produce yellow-to-green, thick, mucoid discharge 5:

• Caused by aerobic enteric bacteria with variable vaginal inflammation 5
• The discharge has a "foul, rather rotten smell" in severe cases, distinct from the fishy odor of BV 5
• The vagina appears red and edematous, potentially with small erosions 5
• Microscopy shows leukocytes and immature epithelial cells 5
• Prevalence is 7-12%, less common than BV 5

Cervicitis

Mucopurulent cervical discharge from Chlamydia trachomatis or Neisseria gonorrhoeae can present as vaginal discharge 3, 6:

• Look for cervical friability, hyperemia, and mucopurulent discharge from the cervical os 3
• This represents upper tract infection requiring different management than simple vaginitis 6

Critical Diagnostic Algorithm

When evaluating green discharge, perform these essential office tests: 1

1. Vaginal pH testing: Elevated (>4.5) in trichomoniasis and BV; normal (<4.5) in candidiasis 1
2. Wet mount examination: Look for motile trichomonads, clue cells (BV), or increased WBCs 3, 1
3. Whiff test: Fishy odor with KOH suggests BV, not trichomoniasis 3, 1
4. Cervical inspection: Assess for strawberry cervix (trichomoniasis) or mucopurulent discharge (cervicitis) 3

Common Pitfalls to Avoid

• Do not assume green discharge is always trichomoniasis—while this is the most characteristic cause, BV and aerobic vaginitis can present similarly 2, 5
• Do not rely on symptoms alone—physical examination with office laboratory testing is essential for accurate diagnosis 1
• Do not forget to screen for other STIs when trichomoniasis is diagnosed, as it indicates sexual transmission risk 2
• Do not treat trichomoniasis without treating sexual partners—this is the most common cause of treatment failure 2
• Do not confuse the lack of inflammation in BV with the prominent inflammation of trichomoniasis—this clinical distinction is crucial 2