What causes menstrual odor?

Causes of Menstrual Odor

Menstrual odor is primarily caused by bacterial overgrowth, particularly bacterial vaginosis (BV), which occurs when normal hydrogen peroxide-producing Lactobacillus species are replaced by anaerobic bacteria, Gardnerella vaginalis, and Mycoplasma hominis. 1, 2

Primary Causes of Menstrual Odor

• Bacterial Vaginosis (BV): The most prevalent cause of vaginal discharge and malodor, characterized by an imbalance in vaginal microbiota 1
• Organic acids: These arise as metabolic byproducts of vaginal bacterial flora and are the direct cause of vaginal odor 3
• Poor menstrual hygiene practices: Inadequate hygiene during menstruation is strongly associated with bacterial vaginosis and subsequent odor 4
• Blood exposure to air: When menstrual blood mixes with normal vaginal bacteria and is exposed to air, it can produce distinctive odors 2

Bacterial Vaginosis and Odor

BV is characterized by specific clinical findings:

• A homogeneous, white discharge that smoothly coats vaginal walls 1
• Presence of clue cells (bacteria-covered epithelial cells) on microscopic examination 1
• Vaginal fluid pH greater than 4.5 1
• A distinctive fishy odor, especially noticeable after adding 10% KOH (positive "whiff test") 1

Factors Contributing to Menstrual Odor

• Douching: Consistently associated with bacterial vaginosis and subsequent odor 5, 6
• Inadequate frequency of bathing: Daily bathing shows a slight protective effect against BV compared to less frequent bathing (PR: 1.06,95% CI: 1.02-1.12) 5
• Use of cloth instead of sanitary pads: Women using cloth as absorbent are more prone to develop BV than those using sanitary pads 4
• Poor sanitation: Unsatisfactory latrine sanitation is strongly associated with BV 4
• Hormonal fluctuations: Changes during the menstrual cycle affect the composition of vaginal flora and organic acid production 3

Diagnostic Approach

When evaluating menstrual odor, healthcare providers should:

• Perform microscopic examination of vaginal discharge using saline and 10% KOH preparations 1
• Look for clue cells, which are characteristic of BV 1
• Measure vaginal pH (normal is <4.5; elevated in BV) 1
• Perform the "whiff test" by adding 10% KOH to vaginal secretions and checking for a fishy odor 1

Management Considerations

• Treat underlying BV: Metronidazole 500 mg orally twice daily for 7 days is the recommended treatment for BV 1, 2
• Improve menstrual hygiene: Use of proper sanitary products and regular changing of menstrual protection 4
• Avoid douching: This practice disrupts normal vaginal flora and is associated with increased risk of BV 5, 7
• Consider probiotic supplementation: Probiotics can improve BV cure rates, especially when used as complementary therapy with antibiotics 2

Important Caveats

• Up to 50% of women with BV may be asymptomatic despite having the condition 1
• Treatment of male sexual partners has not been shown to prevent recurrence of BV 1, 2
• BV has a high recurrence rate (50-80% within a year) even after appropriate treatment 2
• Certain intimate hygiene products and practices can disrupt vaginal flora and contribute to odor 7

Remember that persistent or severe odor, especially when accompanied by other symptoms like itching, burning, or unusual discharge, warrants medical evaluation to rule out infections or other gynecological conditions 1, 6.