Vaginal Odor: Common Causes

"Vaginal odor" is not a diagnosis, but a symptom. It is most often associated with changes in the microbiota and increased acidity (or more accurately, alkalinity) of the vaginal environment, as in bacterial vaginosis. Less commonly, it is associated with trichomoniasis, and less commonly with aerobic vaginitis, desquamative inflammatory vaginitis, atrophic changes during menopause, a long-term foreign body (such as a forgotten tampon), or a fistula. It is important to understand that odor almost always accompanies discharge and other symptoms, so a diagnosis is made based on a combination of complaints, examination, and tests. [1]

Bacterial vaginosis is the most common cause of a "fishy" odor: it arises from amines produced by anaerobic bacteria when the microbiota shifts from a lactobacilli-dominated to a polymicrobial community. Trichomoniasis (a parasitic infection) causes a strong, musty odor, and the discharge is often yellowish-green and foamy. Candidiasis is usually not accompanied by a distinct odor, which helps differentiate it from vaginosis and trichomoniasis. [2]

A separate group of causes are conditions with inflammation and high vaginal pH in non-pregnant women: aerobic vaginitis and desquamative inflammatory vaginitis. These are less common and can produce a "putrid" or pungent odor, thicker yellowish discharge, and soreness. They require a different approach than bacterial vaginosis. During perimenopause, an unpleasant odor may be a consequence of estrogen deficiency associated with urogenital disorders of menopause: the mucosa thins and the pH rises, facilitating the growth of opportunistic bacteria. [3]

Finally, a persistent "foul" odor mixed with blood and the ineffectiveness of standard treatment always prompts a search for a foreign body, or less commonly, fistulas or tumors. Removing the foreign object (tampon, piece of condom, etc.) often resolves the problem immediately, while delaying evaluation increases the risk of ulceration, bleeding, and even fistula formation. [4]

Epidemiology

Bacterial vaginosis is one of the most common causes of abnormal discharge in women of reproductive age. According to systematic reviews and data from the World Health Organization, the global prevalence is approximately 23-29 percent among women of reproductive age, with regional variations. This high prevalence and frequent recurrence pose a significant clinical and social burden. [5]

Trichomoniasis is the most common curable sexually transmitted infection in women; the exact proportions vary by country, but its contribution to the structure of causes of foul-smelling discharge is significant, especially in high-risk groups. Importantly, a seven-day course of metronidazole is considered preferable for women with human immunodeficiency virus (HIV), as single-dose regimens are less effective. This reflects the different microbiota and immune characteristics of this cohort. [6]

Aerobic vaginitis and desquamative inflammatory vaginitis are less common: according to various sources, their incidence ranges from a fraction of a percent to several percent among patients with persistent symptoms. However, the true prevalence figures are underestimated due to poor recognition and the lack of a "gold standard" for diagnosis in routine practice. [7]

It is also worth remembering about atypical sources of odor: foreign bodies (usually a forgotten tampon) are not uncommon in outpatient practice and should always be excluded in cases of prolonged foul-smelling discharge, bloody “smearing” and pain syndrome without a clear cause. [8]

Table 1. Approximate proportion of causes of unpleasant odor (in the population of symptomatic patients)

Cause	Estimated prevalence	Note
Bacterial vaginosis	23-29% in the general population; higher among symptomatic	A common cause of a fishy smell
Trichomoniasis	Leading curable STI	For HIV-positive individuals, a 7-day course is preferred.
Aerobic/desquamative vaginitis	0.8-4.3% (estimated)	Underestimated due to diagnosis
Foreign bodies	The exact figures are unknown.	Always exclude in case of long-term "smelly" process

Reasons

Bacterial vaginosis occurs when the dominance of lactobacilli (especially Lactobacillus crispatus) shifts to polymicrobial communities rich in anaerobes (Gardnerella, Prevotella, Atopobium/Fannyhessea, etc.). The amines they produce (trimethylamine, etc.) produce a characteristic "fishy" odor. Clinically, the diagnosis is confirmed using the Amsel criteria or the Nugent scale. [9]

Trichomoniasis is caused by the protozoan Trichomonas vaginalis. The parasite damages the epithelium, increases the white blood cell count, raises the pH, and often produces a sharp, musty odor and foamy, yellowish-green discharge. Important: wet microscopy is insensitive, so molecular tests are preferred. [10]

Aerobic vaginitis and desquamative inflammatory vaginitis are inflammatory phenotypes characterized by a deficiency of lactobacilli, a predominance of aerobic flora (group B streptococci, E. coli, etc.), a high pH, and severe inflammation. Clinically, we most often see a yellowish, thick discharge with a "putrid" odor, soreness, petechiae, and often dyspareunia. This is not a "variant of bacterial vaginosis," but a different entity with different treatment approaches. [11]

Finally, foreign bodies and urogenital fistulas can cause odor. The retention of a foreign object creates a "focus" of infection, ulceration, and bleeding; the odor is pungent and "putrid." Treatment involves immediate removal of the object and sanitation. During menopause and the postpartum period, atrophic changes in the mucosa and an increase in pH play a role, facilitating colonization by opportunistic flora. [12]

Risk factors

For bacterial vaginosis, risk factors include new or multiple sexual partners, lack of barrier protection, vaginal douching, previous episodes of vaginosis, and possibly certain types of the partner's vaginal microbiota. Associations with the intrauterine system are discussed, but they are not causal. [13]

For trichomoniasis - unprotected contact, the presence of other sexually transmitted infections, etc. In women with human immunodeficiency virus, a higher frequency and lower effectiveness of standard single-dose regimens are noted; this explains the shift in recommendations to seven-day courses of metronidazole. [14]

Aerobic and desquamative vaginitis are more common during perimenopause, with decreased estrogen levels, after frequent use of detergents and tampons, and following antibiotic therapy. These conditions often recur and require individualized strategies to maintain remission. [15]

Separately, we note "non-infectious" odor triggers: tampon/menstrual cup retention, latex residue, and, rarely, fistulas. Any "chronic odor" with traces of blood and ineffective treatment is a reason to specifically seek these causes. [16]

Table 2. Risk factors by groups

State	Main factors	Comments
Bacterial vaginosis	Sexual factors, douching, relapses	Often recurs
Trichomoniasis	Unprotected contact associated with STIs	HIV has a higher risk and different tactics
Aerobic/desquamative vaginitis	Age, low estrogen, aggressive hygiene	Inflammatory phenotype
Foreign bodies	Forgotten tampon, fragments of products	A sharp "putrid" smell, blood

Pathogenesis

In bacterial vaginosis, the predominance of lactobacilli (which maintain an acidic pH) gives way to polymicrobial communities with a predominance of anaerobes. The pH increases (usually ≥4.5), "clue cells"—epithelial cells with adherent bacteria—appear, and amines responsible for the "fishy" odor are released. Inflammation is usually minimal, which distinguishes vaginosis from inflammatory forms of vaginitis. [17]

Trichomonas damage the epithelium and increase leukocyte influx, increase pH, and alter the microbiota, which explains the distinct odor and foamy consistency of the discharge. Wet microscopy quickly loses sensitivity after sample collection, so today the emphasis is on nucleic acid amplification tests. [18]

Aerobic and desquamative vaginitis are pro-inflammatory conditions: few lactobacilli, many leukocytes, often parabasal cells (a sign of epithelial "stress"), and an increased pH. Clinically, this is characterized by severe pain, swelling, petechiae, sometimes erosions, and a more "heavy" odor. [19]

During menopause, estrogen deficiency thins the mucous membrane, increases pH, and reduces protective lactobacilli, creating conditions conducive to the growth of opportunistic microbes and the development of odor without overt infection. Therefore, in some patients, therapy is aimed not at antibiotics, but at restoring the mucous membrane and pH. [20]

Symptoms

The odor is almost always associated with the nature of the discharge and the condition of the mucous membrane. Bacterial vaginosis is typically characterized by thin, uniform, grayish-white discharge and a "fishy" odor that intensifies after intercourse. Itching and burning are usually absent or moderate. The pH is often ≥4.5. [21]

With trichomoniasis, the discharge is more profuse, yellowish-green, often foamy, and has a strong odor; itching, burning, dyspareunia, and dysuria are possible. Some women do not present with significant complaints, so testing is important even in high-risk situations. [22]

Aerobic and desquamative vaginitis produce thick yellow or yellow-green discharge with a "putrid" odor, pain, swelling, and redness. The pH is often above 5.0, and examination reveals petechiae and vaginal wall tenderness. Microscopic examination reveals numerous leukocytes and parabasal cells. [23]

A persistent “fetid” odor with bloody impurities that does not respond to conventional therapy is a “red flag” for a foreign body or fistula and requires immediate examination in a mirror and, if necessary, instrumental evaluation. [24]

Table 3. Odor and discharge: clinical clues

State	Smell	Discharge	Additional features
Bacterial vaginosis	"Fish"	Thin, grey-white, uniform	pH ≥4.5, "key cells"
Trichomoniasis	Sharp, musty	Yellow-green, foamy	Itching/burning, pH↑, leukocytes
Aerobic/desquamative vaginitis	"Putrefactive"	Thick, yellowish	Inflammation, petechiae, pH >5
Foreign body	Sharply foul-smelling	Purulent-bloody	Pain, sometimes contact bleeding

Forms and stages

In bacterial vaginosis, there are no "stages" but rather diagnostic levels: Amsel clinical criteria (≥3 of 4 signs) and Nugent microbiological score (7-10 points - vaginosis; 4-6 - intermediate flora; 0-3 - lactobacilli dominance). "Intermediate" flora may correspond to the "transitional" stage and is sometimes accompanied by a moderate odor. [25]

Trichomoniasis also has no stages; a distinction is made between symptomatic/asymptomatic progression and complicated cases (pregnancy, human immunodeficiency virus infection, relapses, and resistance). This influences the choice of treatment regimen and monitoring of cure. [26]

Aerobic vaginitis is assessed based on a combination of clinical and microscopic findings: high pH, leukocytes, decreased lactobacilli, and the presence of aerobic bacteria. Scoring scales and combined criteria (clinical + microscopic) are proposed. Desquamative inflammatory vaginitis is a diagnosis of exclusion: the required combination of symptoms, pH > 4.5, numerous leukocytes and parabasal cells, and exclusion of vaginosis, trichomoniasis, and candidiasis. [27]

In case of atrophic changes in menopausal patients, the severity of the urogenital disorders of menopause (dryness, burning, dyspareunia) and pH are assessed separately: this helps to choose hormonal or non-hormonal local therapy, which often eliminates the odor. [28]

Complications and consequences

Bacterial vaginosis is associated with an increased risk of acquiring human immunodeficiency virus and other sexually transmitted infections, as well as adverse pregnancy outcomes (preterm birth, low birth weight, premature rupture of membranes). This makes timely diagnosis and treatment not only convenient but also a preventative measure. [29]

Trichomoniasis in pregnant women is also associated with preterm birth and low birth weight; treatment reduces symptoms and the likelihood of transmission to partners, and in women with human immunodeficiency virus, adverse outcomes. [30]

Recurrent bacterial vaginosis impairs quality of life, impacts sexual function and psycho-emotional state, and requires long-term or multi-stage treatment regimens. Incorrect self-diagnosis and self-treatment can delay treatment and increase the risk of missing other causes (foreign body, fistula). [31]

Desquamative inflammatory vaginitis and aerobic vaginitis can cause persistent pain, dyspareunia, and frequent relapses; maintenance therapy often requires months. Adequate diagnosis is essential for selecting an effective approach. [32]

Diagnostics

Diagnosis begins with a questionnaire and speculum examination: the nature of the discharge and the pH of the vaginal contents are assessed, and an "amine" ("effervescent") test with potassium hydroxide solution is performed. For bacterial vaginosis, the Amsel criteria and/or Nugent's Gram stain are used. If a laboratory is not available, validated rapid tests are used. [33]

Trichomoniasis should preferably be confirmed by nucleic acid amplification: wet microscopy is not very sensitive (especially within minutes of taking the smear), culture is better, but inferior to molecular tests; modern panels for vaginitis determine the likelihood of bacterial vaginosis, the presence of trichomoniasis and candidiasis in a single smear. [34]

If aerobic/desquamative vaginitis is suspected, a fresh smear is examined microscopically: leukocytes, parabasal cells, the absence of lactobacilli, and "mature" aerobic forms are looked for; pH is assessed. This is a diagnosis of exclusion: bacterial vaginosis, candidiasis, and trichomoniasis must be ruled out. [35]

If a foreign body or fistula is suspected, a speculum examination is performed, and if necessary, an ultrasound, colposcopy, or endoscopic revision is performed. Removal of the foreign object is both a diagnostic and therapeutic procedure. [36]

Table 4. Key diagnostic tests

Task	Test	What does it give?	Comment
Confirm bacterial vaginosis	Amsel criteria, Nugent scale	Clinical and microbiological criteria	Primary care standard
Detect trichomoniasis	Nucleic acid amplification tests	High sensitivity/specificity	Better than wet microscopy
Rule out aerobic/desquamative vaginitis	Wet smear microscopy, pH	Leukocytes, parabasal cells, pH > 4.5	Diagnosis of exclusion
Identify "rare" causes	Inspection, targeted visualization	Foreign body, fistula	We treat immediately upon discovery.

Differential diagnosis

The first thing to distinguish is bacterial vaginosis and candidiasis. With candidiasis, odor is usually not the primary symptom, and itching and a cottage cheese-like discharge predominate; pH often remains normal. This is the opposite of vaginosis, where pH is elevated and itching is minimal. Incorrect self-medication with antifungal medications can worsen vaginosis. [37]

The second is bacterial vaginosis versus aerobic/desquamative vaginitis. In the latter case, there is more inflammation, pain, and petechiae, a higher pH, and parabasal cells; a combination of a topical antibiotic and an anti-inflammatory agent is often helpful, while metronidazole/clindamycin or secnidazole are effective for vaginosis. [38]

Third, trichomoniasis versus bacterial vaginosis: trichomoniasis is often characterized by a frothy, yellowish-green discharge, a strong odor, and severe inflammation; nucleic acid amplification tests resolve the issue more quickly and accurately than wet microscopy. If the result is positive, the sexual partner must also be treated. [39]

Fourth, exclude foreign bodies and mucosal atrophy during menopause. These causes are often underestimated, although removal of the foreign body or local hormonal therapy for atrophy eliminates the odor without antibiotics. [40]

Table 5. “Similar, but not the same”: brief differentiation

Pair	What do symptoms "vote" for?	What decides
Bacterial vaginosis vs. candidiasis	Fishy odor and pH ↑ vs. itching and cheesy discharge	pH, microscopy/Nugent
Bacterial vaginosis vs aerobic/desquamative	Minimal inflammation vs. pain, petechiae, leukocytes	Wet smear, clinical
Bacterial vaginosis vs. trichomoniasis	Uniform gray-white or foamy yellow-green discharge	Nucleic acid amplification tests
Infection vs. foreign body/atrophy	Relapses without treatment effect	Examination/removal, pH, hormone therapy for atrophy

Treatment

Bacterial vaginosis (primary episode). The recommended regimens are metronidazole 500 mg orally twice daily for 7 days, or 0.75% metronidazole gel intravaginally for 5 days, or clindamycin (oral/2% cream). Single-dose secnidazole 2 g is a modern oral alternative approved on the basis of randomized trials. The choice of dosage form should be based on preferences, compatibility with alcohol, and plans (e.g., pregnancy). [41]

Bacterial vaginosis (recurrent). After the standard course, a multi-step regimen may be possible: metronidazole or tinidazole orally for 7 days → boric acid 600 mg intravaginally for 21 days → 0.75% metronidazole suppressive gel twice weekly for 4-6 months. Monthly metronidazole "pulses" plus fluconazole are being considered. The probiotic Lactobacillus crispatus (Lactin-V), which has been shown to reduce the risk of recurrence after standard treatment, is being discussed and studied, but access is limited. [42]

Trichomoniasis. 5-nitroimidazoles are recommended: for most women, metronidazole 500 mg twice daily for 7 days; a single dose of tinidazole 2 g is an alternative. Sexual partners must be treated, and sexual intercourse should be abstained until treatment is complete. In cases of resistance, consultation with centers that perform susceptibility testing and the selection of alternative regimens is recommended. For women with human immunodeficiency virus (HIV), a seven-day regimen of metronidazole is preferred. [43]

Aerobic and desquamative inflammatory vaginitis. Here, standard regimens "as for vaginosis" are less effective. The best data support intravaginal clindamycin 2% and/or intravaginal hydrocortisone (usually 300-500 mg at night for 2-3 weeks) with possible maintenance therapy once or twice a week for 2-6 months. During menopause, topical estrogens are added, which lower the pH and improve the microbiota. Relapses are common, and treatment is individualized. [44]

Foreign body and atrophy. Removal of the foreign body/sanitation resolves the odor problem immediately in most patients. For urogenital disorders of menopause, topical estrogens, intravaginal dehydroepiandrosterone, the estrogen receptor modulator ospemifene, as well as moisturizers and lubricants are effective—the choice depends on hormonal contraindications. [45]

New and researched approaches. Single-dose secnidazole has simplified the treatment of bacterial vaginosis. Live biotherapeutics (Lactin-V) and vaginal microbiome transplantation (still experimental, but showing promise in severe relapses) are being actively studied for relapse prevention. These strategies aim to "restructure" the microbiota toward lactobacilli dominance, rather than merely temporarily suppress anaerobes. [46]

Table 6. Treatment by main causes

State	First line	Alternatives/additions	Special cases
Bacterial vaginosis (primary)	Metronidazole orally for 7 days or gel for 5 days; clindamycin	Secnidazole 2 g once	Pregnancy: Metronidazole/clindamycin are acceptable.
Bacterial vaginosis (relapse)	Metronidazole suppressive gel 2 times a week for 4-6 months	Boric acid regimen; Lactin-V (as available)	Individualization, relapse prevention
Trichomoniasis	Metronidazole 500 mg 2 times a day for 7 days	Tinidazole 2 g once	Treat partners; for HIV - 7-day regimen
Aerobic/desquamative	Clindamycin 2% and/or hydrocortisone intravaginally	Maintenance therapy; local estrogens	Frequent relapses, long-term control
Foreign body/atrophy	Removal; local estrogens for atrophy	Humectants, ospemifene, DHEA	Immediate inspection in the mirrors

Prevention

Effective preventative measures include barrier protection during sex, avoiding vaginal douching and aggressive hygiene, using neutral intimate products, choosing cotton underwear, and changing wet clothing after sports/swimming. These steps support lactobacilli dominance and reduce the risk of bacterial vaginosis and non-specific inflammatory conditions. [47]

In perimenopausal and postmenopausal patients, odor prevention often involves treatment of urogenital disorders of menopause: topical estrogens, dehydroepiandrosterone, ospemifene, as well as regular moisturizers and lubricants. This lowers the pH, improves mucosal nutrition, and reduces the frequency of "nonspecific" complaints, including odor. [48]

Forecast

The prognosis for bacterial vaginosis and trichomoniasis is favorable: appropriate therapy relieves symptoms, including odor, in most patients. The main problem with vaginosis is recurrence within 3-12 months; in such cases, suppressive regimens, adjuvant approaches, and risk factor management are beneficial. [49]

In aerobic and desquamative vaginitis, the prognosis depends on treatment adherence and the availability of maintenance therapy: remissions are achievable, but relapses are frequent. In cases of mucosal atrophy, correcting estrogen deficiency usually produces a lasting effect. In cases of foreign body removal, the problem is resolved immediately; it is important not to overlook this cause during the initial assessment. [50]

FAQ

• Does odor always mean infection?

No. Often yes, but not always. Odor can be caused by bacterial vaginosis and trichomoniasis, but it can also occur with mucosal atrophy during menopause, aerobic/desquamative vaginitis, and a foreign body. An examination and simple tests (pH, microscopy, molecular panels) are the answer. [51]

• Is it possible to treat thrush with suppositories if there is a smell?

This is a common mistake. Candidiasis usually doesn't produce a strong odor. If the primary complaint is a "fishy" or strong odor, bacterial vaginosis or trichomoniasis is more likely, and antifungal suppositories won't help. Proper diagnosis and targeted treatment are needed. [52]

• What to do if vaginosis comes back again and again?

There are suppressive regimens (metronidazole gel twice a week for 4-6 months), multi-step algorithms with boric acid, and research approaches such as the live biotherapeutics Lactin-V and vaginal microbiome transplant. The choice is discussed individually. [53]

• Should my sexual partner be treated?

For trichomoniasis, this is mandatory. For bacterial vaginosis, routine treatment of partners is not recommended, but in cases of frequent relapses, the approach is discussed individually and according to local protocols. Abstinence from sexual intercourse is recommended until treatment is completed and symptoms disappear. [54]

• What "new" remedies actually work against vaginosis odor?

Among the "new" ones are secnidazole (single dose) and the biotherapeutic Lactin-V (currently with limited availability), which reduces relapses after standard treatment. Vaginal microbiome transplant strategies are being explored, but so far only in clinical trials and isolated reports. [55]