Vaginal Infections — Causes, Symptoms & Treatment Guide — Symptoms, Causes & Treatment | MyMedicPlus

Vaginal infections are among the most common gynaecological complaints — accounting for millions of GP and sexual health clinic consultations annually. The three most common types are: bacterial vaginosis (BV — the most prevalent, caused by overgrowth of anaerobic bacteria and depletion of protective Lactobacillus species, characterised by malodorous discharge with elevated vaginal pH), vulvovaginal candidiasis (VVC — 'thrush' — caused by Candida species overgrowth, typically producing a thick, white, cottage-cheese discharge with vulval itch and soreness), and trichomoniasis (a sexually transmitted parasitic infection from Trichomonas vaginalis). It is important to differentiate these clinically, as treatments differ — and misdiagnosis leads to treatment failure and potential complications. Vaginal discharge in women may also arise from physiological causes (normal cyclical variation), STIs (chlamydia, gonorrhoea causing cervicitis), and non-infective causes (contact dermatitis, lichen sclerosus, atrophic vaginitis). A healthy vaginal ecosystem is dominated by Lactobacillus species (particularly L. crispatus and L. iners) that produce lactic acid, maintaining a low pH (3.5-4.5) that inhibits pathogen growth.

Bacterial vaginosis (BV): polymicrobial overgrowth — particularly Gardnerella vaginalis, Prevotella, Mobiluncus, and Mycoplasma hominis — replacing the protective Lactobacillus-dominant flora. Risk factors: new or multiple sexual partners (sexual activity disrupts the vaginal microbiome, though BV is not classified as an STI), vaginal douching (disrupts normal flora — strongly discouraged), smoking (reduces Lactobacillus colonisation), antibiotic use, intrauterine devices (IUD), and black ethnicity (associated with less stable Lactobacillus-dominant flora in epidemiological studies). Vulvovaginal candidiasis (VVC/thrush): Candida albicans (80-90% of cases), C. glabrata (more resistant to azoles), and other Candida species. Risk factors: antibiotic use (disrupts Lactobacillus — the most common trigger), pregnancy (high oestrogen promotes Candida growth), diabetes mellitus (elevated vaginal glucose), immunosuppression (HIV, corticosteroids, chemotherapy), high-oestrogen states, synthetic underwear (warm, moist environment), and tight clothing. Trichomoniasis: caused by Trichomonas vaginalis — a flagellated protozoan, strictly sexually transmitted. Risk factors: new or multiple sexual partners, inconsistent condom use, other STIs (particularly gonorrhoea — co-infection common), and low socioeconomic status. Other vaginal infections: chlamydia and gonorrhoea primarily cause cervicitis (cervical discharge) but may extend to the vagina; herpes simplex virus (HSV) causes vulval ulcers and vaginal discharge; group B Streptococcus (GBS) — asymptomatic vaginal colonisation in pregnancy requires treatment at labour.

Bacterial vaginosis: thin, greyish-white, homogeneous discharge — often described as 'fishy' odour (particularly after intercourse — when semen raises vaginal pH, releasing volatile amines from anaerobic bacteria); mild vulval irritation (but typically less itch than candidiasis); vaginal pH above 4.5; and Whiff test (adding 10% KOH to discharge releases a fishy odour from volatile amines — positive). Vulvovaginal candidiasis (thrush): thick, white, curdy ('cottage cheese') discharge without significant odour; intense vulval and vaginal pruritus (itch — the cardinal symptom); vulval erythema, soreness, swelling, and fissuring; dyspareunia (pain with intercourse); and external dysuria (burning when urine touches inflamed vulva). Vaginal pH is normal (below 4.5). Trichomoniasis: in 50% of women — asymptomatic; when symptomatic — profuse, frothy, yellow-green malodorous discharge; vulval irritation, soreness, and dyspareunia; strawberry cervix (punctate haemorrhages on the cervix — seen in 2-3% — pathognomonic when present); vaginal pH above 4.5. Cervicitis (chlamydia, gonorrhoea): usually asymptomatic; may cause a purulent or mucopurulent cervical discharge (endocervical discharge), post-coital bleeding, and pelvic pain. Atrophic vaginitis (postmenopausal — genitourinary syndrome of menopause — GSM): vaginal dryness, soreness, dyspareunia, and thin bloody or watery discharge from oestrogen-deficient vaginal atrophy — not an infection but presents similarly.

Clinical diagnosis: in women with classic symptoms, BV and VVC can often be diagnosed clinically. Speculum examination: visualises the discharge character (BV — thin grey; VVC — thick white curd; trichomoniasis — frothy yellow), cervical appearance, and any cervicitis. Vaginal pH measurement: pH above 4.5 suggests BV or trichomoniasis (not VVC — pH normal in VVC). Whiff test (KOH): positive in BV. Point-of-care NAAT testing: nucleic acid amplification tests (molecular testing) for Chlamydia trachomatis and Neisseria gonorrhoeae from high vaginal or endocervical swabs — most sensitive tests (above 95%) and recommended in all women presenting with vaginal discharge (to exclude STIs). Trichomonas vaginalis NAAT: more sensitive than wet mount microscopy (80% vs 50% sensitivity) — should be used where available. Microscopy (where available — GUM clinics): high vaginal swab microscopy reveals: clue cells (vaginal epithelial cells studded with adherent bacteria — diagnostic of BV when more than 20% of cells); hyphae and spores (Candida — positive in 50-70% of VVC); and motile trichomonads (Trichomonas vaginalis — present in 60-70% of trichomoniasis). Amsel's criteria (clinical diagnosis of BV — 3 of 4): thin homogeneous discharge, pH above 4.5, positive Whiff test, clue cells on microscopy. Nugent score: Gram stain of high vaginal swab — standardised scoring system for Lactobacillus and anaerobe balance (0-10 scale: 0-3 normal; 4-6 intermediate; 7-10 BV). Culture: for recurrent VVC — identifies non-albicans Candida species and antifungal sensitivities.

Bacterial vaginosis (BV): Metronidazole 400mg orally twice daily for 5-7 days (first-line — 70-80% cure rate at 4 weeks) or metronidazole 0.75% vaginal gel once daily for 5 days; or clindamycin 2% vaginal cream once daily for 7 days (particularly during pregnancy). Recurrent BV (3 or more episodes per year): suppressive vaginal metronidazole gel twice weekly for 16 weeks (after initial treatment); boric acid vaginal suppositories (unlicensed — some evidence); vaginal Lactobacillus products (LACTIN-V — intravaginal Lactobacillus crispatus CTV-05 — Phase 2b trial showed significant reduction in BV recurrence). Avoid douching. Vulvovaginal candidiasis (VVC/thrush): Fluconazole 150mg single oral dose (first-line if not pregnant) — cure rates 85-90%. Intravaginal options: clotrimazole 500mg single pessary, or clotrimazole 100mg pessary for 6 days, or miconazole cream; useful in pregnancy (oral azoles are contraindicated — teratogenic). External cream (clotrimazole, miconazole): relieves vulval itching — apply to external vulva. Recurrent VVC (4 or more episodes per year): fluconazole 150mg every 3 days for 3 doses (induction), then 150mg weekly for 6 months (maintenance — reduces recurrence during treatment period). Consider C. glabrata — resistant to standard azoles; treat with boric acid suppositories 600mg vaginally for 14 days. Trichomoniasis: Metronidazole 400mg twice daily for 5-7 days (or 2g single dose — but higher recurrence rate with single dose); or tinidazole 2g single dose. Sexual partner(s) must be treated simultaneously to prevent reinfection — trichomoniasis is always sexually transmitted. Advise no sexual contact until patient and partner have completed treatment and are symptom-free. Cervicitis (chlamydia): doxycycline 100mg twice daily for 7 days (first-line); gonorrhoea: ceftriaxone 1g IM single dose (plus doxycycline for chlamydia — common co-infection). Test of cure is recommended for gonorrhoea. Partner notification essential for all STIs. Postmenopausal atrophic vaginitis (GSM): vaginal oestrogen (pessary, cream, or ring — very low systemic absorption) — effective and safe for genitourinary symptoms even in women with a history of breast cancer (per NICE 2023 guidance for most women).

Pelvic inflammatory disease (PID — ascending infection from untreated BV or cervicitis to the fallopian tubes and ovaries; causes chronic pelvic pain, tubal infertility, and ectopic pregnancy risk; approximately 15% of untreated chlamydial or gonococcal cervicitis progresses to PID). Tubal infertility and ectopic pregnancy (from PID-related tubal scarring — 12% infertility risk after one episode of PID, rising to 54% after three episodes). Pregnancy complications (BV associated with preterm birth, preterm premature rupture of membranes, and late miscarriage; untreated group B Streptococcus colonisation during labour causes neonatal sepsis and meningitis). Increased HIV susceptibility (BV and trichomoniasis both increase HIV acquisition risk 2-3 fold by disrupting the protective Lactobacillus vaginal barrier). Recurrent vulvovaginal candidiasis (4 or more episodes per year — affects 8% of women; may indicate underlying diabetes, immune deficiency, or azole-resistant Candida glabrata requiring specialist management).

Vaginal douching: strongly discouraged — douching disrupts the protective Lactobacillus-dominant vaginal flora, raises vaginal pH, and significantly increases risk of BV and ascending pelvic inflammatory disease. The vagina is self-cleaning and requires no internal washing. External washing with plain warm water only is recommended. Soap avoidance: use only non-perfumed, unfragranced soap on the vulva (never internally) — perfumed products disrupt vaginal microbiome. Underwear: wear breathable cotton underwear and avoid tight synthetic clothing to reduce the warm, moist environment that promotes Candida growth. Condom use: consistent use of male or female condoms reduces transmission of trichomoniasis, chlamydia, gonorrhoea, and HSV, and may reduce BV recurrence rates (by preventing semen-induced vaginal pH disruption and partner-related microbiome alterations). Antibiotic stewardship: unnecessary antibiotic use disrupts Lactobacillus colonisation — increasing VVC risk; always complete antibiotic courses when prescribed, but avoid unnecessary prescribing. Probiotic Lactobacillus: oral and vaginal Lactobacillus probiotics show modest evidence for prevention of recurrent BV and VVC — not yet recommended as routine treatment but may be considered as adjunct. Diabetes management: well-controlled blood glucose significantly reduces recurrent Candida infections. STI testing: all sexually active women under 25 and those with new or multiple partners should be offered annual chlamydia screening (NCSP — National Chlamydia Screening Programme in England).

See a GP or sexual health clinic for: vaginal discharge that is abnormal in colour, quantity, or smell; first episode of thrush (to confirm diagnosis); symptoms not clearing with over-the-counter treatments; BV symptoms (which cannot be treated OTC with antifungals); symptoms suggestive of trichomoniasis or STI (particularly if new sexual partner); and vaginal discharge in pregnancy. Seek urgent assessment for: pelvic pain with fever (ascending pelvic inflammatory disease — PID — requires prompt antibiotic treatment to prevent tubal infertility); post-coital bleeding or inter-menstrual bleeding; and lower abdominal pain with vaginal discharge. Go to a GUM/sexual health clinic for: STI testing (confidential, free in the UK, no GP referral needed), partner notification, and management of recurrent or treatment-resistant vaginal infections. Sexual health clinics offer same-day testing. Women with recurrent (4 or more episodes per year) vulvovaginal candidiasis should be assessed for diabetes mellitus, immune deficiency, and non-albicans Candida species.