White Milky Vaginal Discharge: Causes and Differential Diagnosis
White milky vaginal discharge is most commonly caused by bacterial vaginosis (BV), which results from replacement of normal protective Lactobacillus species with anaerobic bacteria, Gardnerella vaginalis, and Mycoplasma hominis. 1
Primary Pathophysiologic Mechanism
The normal vaginal ecosystem is maintained by H₂O₂-producing Lactobacillus species that produce lactic acid, hydrogen peroxide, and bacteriocin. 2 In BV, this protective flora is displaced by pathogenic organisms, leading to the characteristic homogeneous, white, noninflammatory discharge that smoothly coats the vaginal walls. 1, 3
Key Diagnostic Features of BV
When evaluating white milky discharge, BV can be diagnosed using the Amsel criteria, requiring three of the following four findings: 1, 3
- Homogeneous, white, noninflammatory discharge that smoothly coats the vaginal walls 1, 3
- Vaginal pH greater than 4.5 (normal pH is 3.8-4.2) 1, 3, 4
- Clue cells on microscopic examination (bacteria attached to epithelial cell borders, >20% of epithelial cells) 1, 3, 4
- Positive whiff test (fishy odor before or after addition of 10% KOH) 1, 3
Alternatively, Gram stain showing a Nugent score ≥4 can confirm the diagnosis. 1, 5
Other Causes to Consider
While BV is the most prevalent cause of vaginal discharge, other conditions can present with white discharge: 1
- Vulvovaginal candidiasis typically presents with a thick, "curdled" white discharge rather than milky, and is associated with vulvar pruritus, normal pH (3.8-4.2), and hyphae or budding yeast on microscopy. 4, 6
- Physiologic discharge from normal cervical mucus production, which maintains normal pH and lacks inflammatory signs. 7
- Cervical infections (chlamydia or gonorrhea) may produce vaginal discharge but typically have other associated findings. 7
Clinical Significance
Up to 50% of women with BV are asymptomatic, so the presence of white milky discharge alone warrants evaluation even without other symptoms. 1, 2 BV is associated with serious complications including: 1
- Pelvic inflammatory disease and endometritis 1
- Adverse pregnancy outcomes (preterm birth, premature rupture of membranes, postpartum endometritis) 1
- Increased susceptibility to sexually transmitted infections 1
Risk Factors
Multiple sexual partners are strongly associated with BV, though women who have never been sexually active are rarely affected. 1, 2 Menstrual cycle changes and hormonal alterations can also trigger BV by affecting cervical barriers and reducing the bacteriostatic effect of cervical mucus. 2
Critical Pitfalls to Avoid
- Do not assume absence of symptoms means absence of disease - 50% of BV cases are asymptomatic. 1, 2
- Do not rely on discharge appearance alone - perform pH testing and microscopy to differentiate BV from candidiasis and other causes. 4, 6
- Do not overlook BV before invasive gynecological procedures, as this increases risk of post-procedure infections. 1
- Screen and treat pregnant women with symptomatic BV due to associations with adverse pregnancy outcomes. 1