What causes vaginal odor and itching?

Causes of Vaginal Odor and Itching

Vaginal odor and itching are most commonly caused by three infections: bacterial vaginosis (40-50% of cases), vulvovaginal candidiasis (20-25%), and trichomoniasis (15-20%), with bacterial vaginosis being the single most common cause when a diagnosis is identified. 1, 2

The Three Main Infectious Causes

1. Bacterial Vaginosis (BV) - Most Common Cause

• BV results from replacement of normal hydrogen peroxide-producing lactobacilli with anaerobic bacteria (Prevotella, Mobiluncus), Gardnerella vaginalis, and Mycoplasma hominis 3, 1
• The hallmark symptom is a fishy vaginal odor, particularly after intercourse or during menstruation, along with a thin, homogeneous white or gray discharge 1, 2
• Itching is typically minimal or absent with BV—if itching is the predominant symptom, consider other diagnoses 3, 1
• Vaginal pH is elevated above 4.5, and the "whiff test" (fishy odor when KOH is applied) is positive 3, 1
• Treatment is metronidazole (oral or intravaginal) or intravaginal clindamycin 1, 2

2. Vulvovaginal Candidiasis - Most Common Cause of Itching

• Candidiasis is the primary cause when intense vulvar itching and irritation are the dominant symptoms 1, 4
• Caused by Candida albicans in most cases, presenting with thick, white, "cottage cheese-like" discharge 3, 1, 5
• Additional symptoms include vulvar burning, vaginal pain, and dyspareunia (painful intercourse) 1, 4
• Vaginal pH remains normal (≤4.5), distinguishing it from BV and trichomoniasis 1, 6
• Treatment options include oral fluconazole 150 mg single dose or intravaginal azoles (clotrimazole, miconazole, terconazole) 1, 4, 2
• Important caveat: 10-20% of women have Candida colonization without symptoms and do not require treatment 1, 6

3. Trichomoniasis - Sexually Transmitted

• Caused by the protozoan Trichomonas vaginalis, presenting with yellow-green, frothy discharge with foul odor 1, 5, 7
• Symptoms include vulvar itching, vaginal irritation, and dysuria 1, 7
• The classic "strawberry cervix" (colpitis macularis) is highly specific but present in only a minority of cases 7
• Vaginal pH is elevated above 4.5 3, 1
• Treatment requires oral metronidazole or tinidazole, and sexual partners must be treated simultaneously to prevent reinfection 1, 2

Diagnostic Approach

The key to diagnosis is measuring vaginal pH and performing microscopic examination of vaginal discharge with both saline and 10% KOH preparations 3, 1:

• pH >4.5 suggests BV or trichomoniasis 3, 1, 6
• Saline microscopy identifies motile trichomonads or clue cells (epithelial cells covered with bacteria, diagnostic of BV) 3, 1
• KOH microscopy reveals yeast or pseudohyphae of Candida 3, 1
• Whiff test (fishy odor with KOH application) indicates BV 3, 1

Less Common Causes

• Atrophic vaginitis from estrogen deficiency causes vaginal dryness, irritation, and dyspareunia 2
• Irritant or allergic vaginitis from soaps, douches, hygiene products, or tight clothing can mimic infectious symptoms 3, 6
• Cervicitis from Chlamydia or gonorrhea may present with vaginal discharge but typically lacks significant odor or itching 3

Critical Red Flags

Do not assume vaginal symptoms are always benign—certain features require immediate evaluation 4:

• Fever, chills, lower abdominal, back, or shoulder pain suggest pelvic inflammatory disease or ectopic pregnancy 4
• Foul-smelling discharge with multiple sexual partners may indicate sexually transmitted infections requiring different treatment 4
• Missed period with vaginal symptoms warrants pregnancy testing 4
• Recurrent infections (≥3 in 6 months) require evaluation for diabetes, immunosuppression, or HIV infection 4, 2

Common Pitfalls to Avoid

• Never treat empirically without confirming diagnosis—symptoms alone cannot reliably distinguish between causes 6, 2
• Avoid douching, which disrupts normal vaginal flora and increases infection risk 1, 6
• Do not treat asymptomatic Candida colonization—approximately 10-20% of women have yeast without symptoms 1, 6
• Remember that laboratory testing fails to identify a cause in a substantial minority of women with vaginal complaints, and physiologic discharge may be misinterpreted as pathologic 3, 6
• If symptoms persist after treatment or recur within 2 months, medical re-evaluation is essential 1