Characteristic Odor of Bacterial Vaginosis
Bacterial vaginosis has a distinctly fishy odor, which becomes more pronounced when the vaginal discharge is exposed to alkaline substances like 10% potassium hydroxide (KOH) during the "whiff test." 1, 2
The Fishy Odor: Pathophysiology and Clinical Significance
- The characteristic fishy smell results from anaerobic bacteria producing enzymes (aminopeptidases and decarboxylases) that break down proteins and convert amino acids into volatile amines 3
- These amines are responsible for both the elevated vaginal pH and the distinctive malodorous discharge that defines BV 3
- The odor is often described as "musty or fishy" and represents one of the four Amsel diagnostic criteria used by the CDC 4, 1
Clinical Detection of the Odor
- The "whiff test" is performed by adding 10% KOH to vaginal discharge on a slide—an immediate amine (fishy) odor confirms BV as one of the diagnostic criteria 1, 2
- The fishy odor may be present before KOH application but becomes more pronounced with alkalinization 1, 5
- This odor is a key distinguishing feature: BV causes malodor without significant vulvar irritation, unlike other vaginal infections 6
Diagnostic Context
- For clinical diagnosis, the fishy odor must be present alongside two other Amsel criteria: homogeneous white discharge coating vaginal walls, clue cells on microscopy, or vaginal pH >4.5 2, 5
- The CDC emphasizes that BV is the most prevalent cause of vaginal discharge or malodor, though approximately 50% of women meeting diagnostic criteria remain asymptomatic 2, 6
- Many symptomatic patients specifically report the malodorous discharge as their primary complaint, with the characteristic copious discharge developing if left untreated 3, 7