What causes vaginal odor?

Causes of Vaginal Odor

The most common causes of vaginal odor are bacterial vaginosis (BV), trichomoniasis, and less frequently, vulvovaginal candidiasis, with bacterial vaginosis being the predominant cause in 40-50% of cases. 1, 2

Primary Causes of Vaginal Odor

1. Bacterial Vaginosis (BV)

• Most common cause (40-50% of vaginal odor cases) 2
• Characterized by:
  • Fishy or musty odor (particularly noticeable after intercourse or during menstruation)
  • Thin, homogeneous, white discharge that smoothly coats vaginal walls
  • Elevated vaginal pH (>4.5)
  • Positive "whiff test" (fishy odor when 10% KOH is added to discharge)
  • Presence of clue cells on microscopic examination 3, 1
• Caused by replacement of normal hydrogen peroxide-producing Lactobacillus with anaerobic bacteria (Prevotella, Mobiluncus), Gardnerella vaginalis, and Mycoplasma hominis 3, 1

2. Trichomoniasis

• Accounts for 15-20% of vaginitis cases 2
• Characterized by:
  • Malodorous discharge
  • Profuse, yellow-green vaginal discharge
  • Vaginal or vulvar irritation
  • Often accompanied by itching and burning 4
• Caused by the protozoan Trichomonas vaginalis 3

3. Vulvovaginal Candidiasis

• Less commonly associated with odor (20-25% of vaginitis cases) 2
• Characterized by:
  • Minimal or no odor (distinguishing feature from BV and trichomoniasis)
  • Thick, white "cottage cheese-like" discharge
  • Intense itching and burning
  • Normal vaginal pH (≤4.5) 1, 2
• Usually caused by Candida albicans 3

Less Common Causes

4. Noninfectious Causes (5-10% of cases) 2

• Atrophic vaginitis: Common in postmenopausal women due to decreased estrogen
• Chemical irritants: Soaps, douches, spermicides, feminine hygiene products
• Allergic reactions: To latex condoms, spermicides, or hygiene products
• Foreign bodies: Retained tampons or other objects can cause malodorous discharge
• Inflammatory conditions: Such as desquamative inflammatory vaginitis 5

5. Other Considerations

• Cervical or vaginal infections with Chlamydia or Gonorrhea can occasionally cause discharge with odor 3
• Poor hygiene or excessive sweating in the genital area
• Rectovaginal fistulas (rare but can cause persistent fecal odor) 5

Diagnostic Approach

The diagnosis of vaginal odor causes is based on:

1. Vaginal pH measurement:

   • pH >4.5 suggests BV or trichomoniasis
   • pH ≤4.5 suggests candidiasis or normal flora 1

2. Microscopic examination:

   • Saline wet mount: To identify clue cells (BV) or motile trichomonads
   • 10% KOH preparation: To identify yeast or pseudohyphae 3

3. Whiff test: Fishy odor after adding 10% KOH to discharge strongly suggests BV 3, 1

Clinical Pearls and Pitfalls

• Up to 50% of women with bacterial vaginosis may be asymptomatic despite having the condition 3
• Symptoms alone cannot reliably distinguish between causes of vaginitis; laboratory testing is essential for accurate diagnosis 6
• The absence of perceived odor makes bacterial vaginosis unlikely (LR, 0.07) 6
• Women who have never been sexually active rarely develop bacterial vaginosis 3
• Self-diagnosis and self-treatment with over-the-counter products can mask symptoms and delay proper diagnosis 5
• In approximately one-third of women presenting with genital malodor, no specific cause is identified despite thorough evaluation 5

Remember that persistent or recurrent vaginal odor warrants further investigation to rule out more serious conditions or complications, especially in pregnant women where BV increases the risk of preterm labor and other adverse outcomes 1.