Vaginal Discharge and Vaginal Infections: Bacterial Vaginosis, Thrush and Trichomonas

What is vaginal discharge, and what is normal?

Vaginal discharge is made up of mucus from the glands of the cervix, fluid from the vaginal walls and shed cells. It keeps the vagina moist, protects the tissue and provides a natural defence against micro-organisms. Discharge is normal in women of reproductive age; the amount varies between women and in the same woman over time.

In a healthy vagina the dominant bacteria are lactobacilli. They produce lactic acid, keeping the vagina mildly acidic (pH about 3.8-4.5) and making it harder for harmful organisms to grow. When this balance is disturbed, infections develop more easily.

Normal discharge is usually clear or milky white, has no unpleasant smell and does not cause itching or burning. It may leave a pale yellowish mark on underwear when it dries; this alone is not a sign of infection.

Changes through the menstrual cycle

• Just after a period: there is little discharge and the vagina may feel drier.
• Towards ovulation: as oestrogen rises, discharge increases and becomes clear, slippery and stretchy, like raw egg white. This mucus helps sperm travel into the uterus.
• After ovulation: under the effect of progesterone, discharge decreases and becomes thicker, stickier and whiter.
• Before a period: white, thicker discharge is common, and brownish spotting may occur at the start and end of a period.

Sexual arousal, the contraceptive pill, an intrauterine device and intense exercise can also change the amount of discharge.

Pregnancy, breastfeeding and menopause

In pregnancy, higher oestrogen levels and increased blood flow to the vagina make discharge noticeably heavier; thin, white, mildly scented discharge is normal. However, a sudden increase in watery fluid may mean the waters are leaking, and bloody or pink discharge may indicate another problem, so both should be reported to your doctor.

While breastfeeding, oestrogen is low, so discharge may decrease and the vagina may feel dry. After menopause, falling oestrogen thins the vaginal wall and reduces discharge; dryness, burning and pain during intercourse may develop (genitourinary syndrome of menopause).

When is discharge not normal?

What matters is a change from what is usual for you. The following changes suggest an infection or another problem:

• A change in colour to grey, green or deep yellow
• An unpleasant or fishy smell, especially after intercourse or a period
• A frothy, very watery or cottage cheese-like consistency
• Itching, burning, redness or swelling of the vulva
• Burning on the outside when passing urine, or pain during intercourse
• Blood in the discharge or bleeding after intercourse
• Pelvic pain or fever

Common causes of vaginal infection and how they are diagnosed

The three most common causes of vaginal inflammation (vaginitis) are bacterial vaginosis, vaginal thrush (vulvovaginal candidiasis) and trichomonas infection (trichomoniasis). Their symptoms can overlap, and two infections are sometimes present together. The cause therefore cannot always be told from symptoms alone; self-diagnosis of thrush is known to be often wrong.

Assessment includes:

• History: when symptoms began, the features of the discharge, the menstrual cycle, the possibility of pregnancy, recent antibiotics, sexual activity and any new partner.
• Speculum examination: the vagina and cervix are inspected for the appearance of the discharge, redness, sores or a foreign body.
• pH testing: the acidity of the discharge is measured with a test strip. In bacterial vaginosis and trichomonas the pH is usually above 4.5; in thrush it is usually normal.
• Microscopy: a sample of discharge is mixed with saline and potassium hydroxide (KOH) and examined under the microscope. Yeast cells, moving trichomonads or the "clue cells" typical of bacterial vaginosis may be seen. A fishy smell when KOH is added (the whiff test) supports bacterial vaginosis.
• Laboratory tests: when needed, a yeast culture and nucleic acid amplification tests (NAAT, PCR-type molecular tests) for trichomonas, chlamydia and gonorrhoea are used.

Bacterial vaginosis

What is it and what causes it?

Bacterial vaginosis (BV) is the most common cause of abnormal discharge in women of reproductive age. It is not caused by catching a single germ; rather, the protective lactobacilli decrease and are replaced by other bacteria such as Gardnerella vaginalis. It is not classed as a sexually transmitted infection in the traditional sense, but it is linked to sexual activity. A new or more than one partner, not using condoms, vaginal douching and smoking increase the risk. It can also occur in women who have never had sex.

Symptoms

Many women with BV have no symptoms. When present, the typical features are a thin, uniform, greyish-white discharge and a fishy smell, which is often more noticeable after intercourse and during a period. Itching and redness are usually not prominent.

Diagnosis

In the clinic, BV is usually diagnosed with the Amsel criteria. At least three of these four findings are enough: thin, uniform discharge; a pH above 4.5; a fishy smell when KOH is added; and clue cells on microscopy. The Nugent score, which grades the types of bacteria on a stained slide in the laboratory, is used mainly as the reference method in research. Molecular tests developed for BV are also available. Culture for Gardnerella is not recommended, as this bacterium is also found in healthy women.

Treatment

Treatment is recommended for all women with symptoms. Guideline first-line options are oral metronidazole, metronidazole vaginal gel or clindamycin vaginal cream; tinidazole, secnidazole and other forms of clindamycin are alternatives. The medicine, its form and duration are decided by your doctor, and it is important to finish the course even if symptoms settle. Because clindamycin cream is oil-based and can weaken latex condoms and diaphragms, these methods should not be relied on during treatment and for a few days afterwards. Treatment is usually not needed for women without symptoms, although it may be recommended before certain procedures inside the uterus or operations, depending on the doctor's assessment.

Partner treatment

Current guidelines do not recommend routine treatment of male partners, as older studies found it did not affect cure or recurrence in women. However, a randomised trial published in 2025 reported that treating the male partner in monogamous relationships with an oral and a topical antibiotic reduced BV recurrence. Women with recurrent BV can discuss this option with their doctor. In women with female partners, BV may also be present in the partner, and assessment is appropriate if the partner has symptoms.

Recurrence

BV responds well to treatment but often comes back; studies report recurrence within a year in about half of women or more. With frequent recurrences, a longer course or suppressive vaginal treatment used a few times a week for several months may be planned. Using condoms and avoiding douching may lower the risk of recurrence.

Bacterial vaginosis in pregnancy

In pregnancy, BV has been linked to preterm birth, premature rupture of the membranes and infection of the uterus after birth. Treatment is recommended for pregnant women with symptoms; metronidazole and clindamycin can be used in pregnancy. Routine BV screening is not recommended for pregnant women without symptoms who are at low risk of preterm birth. For women with a previous preterm birth, the decision about screening is made individually by the doctor.

Vaginal thrush (vulvovaginal candidiasis)

What is it and what causes it?

Thrush is usually caused by the yeast Candida albicans. Candida lives in the vagina of many healthy women without causing symptoms; when the balance is disturbed it overgrows and causes symptoms. Many women have thrush at least once in their lives. Antibiotics, pregnancy, poorly controlled diabetes, illnesses or medicines that suppress immunity and oestrogen-containing hormones increase the risk. It is not considered a sexually transmitted infection.

Symptoms

• Marked itching, burning and irritation of the vulva and vagina
• Redness, swelling and sometimes small splits in the skin
• White, thick, cottage cheese-like or more watery discharge, usually without a strong smell
• Pain during intercourse and burning on the outside when passing urine

Diagnosis

Diagnosis is based on examination and microscopy of the discharge with KOH, which may show yeast cells or their branching forms (pseudohyphae). The pH is usually normal. If microscopy is negative but symptoms persist, or if infections keep recurring, a culture identifies the yeast species; some species, such as Candida glabrata, may respond less well to standard medicines. Finding Candida on culture in a woman without symptoms does not, by itself, need treatment.

Treatment

Uncomplicated thrush is treated with short courses of vaginal azole medicines (cream or pessary, for example clotrimazole or miconazole) or oral fluconazole. Thrush is considered "complicated" when symptoms are severe, it recurs often, it is caused by other yeast species, or there is poorly controlled diabetes, reduced immunity or pregnancy; longer or different treatment is then needed. Your doctor decides which medicine to use and for how long.

Women who have previously been diagnosed with thrush by a doctor and have exactly the same symptoms can use over-the-counter vaginal antifungal treatments. However, if symptoms do not settle with treatment or return within two months, an examination is needed. The wrong treatment delays recognition of the real cause, such as BV or trichomonas.

Partner treatment

Routine treatment of partners is not needed. If a male partner has redness, itching or irritation of the head of the penis (balanitis), he can be assessed and treated.

Recurrent thrush

Three or more symptomatic episodes within one year are defined as recurrent vulvovaginal candidiasis (some sources use four or more). The diagnosis is then confirmed with culture, contributing conditions such as diabetes are looked for, and usually a longer course to control the infection is followed by several months of preventive (suppressive) treatment. Symptoms may return in some women after preventive treatment stops, in which case treatment is reviewed.

Thrush in pregnancy

Thrush is more common in pregnancy because of higher oestrogen levels. In pregnancy, vaginal azole medicines used for about a week are recommended. Oral fluconazole is not recommended in pregnancy because some studies have linked it to an increased risk of miscarriage. If you have discharge or itching in pregnancy, it is advisable to speak to your doctor before using any medicine.

Trichomonas infection (trichomoniasis)

What is it and how is it spread?

Trichomoniasis is a sexually transmitted infection caused by a single-celled parasite, Trichomonas vaginalis, and is one of the most common curable sexually transmitted infections worldwide. Without treatment it can persist for months and continue to be passed to partners; it also increases the risk of acquiring other sexually transmitted infections, including HIV.

Symptoms

Many women and men have no symptoms. When present, symptoms may include yellow-green, sometimes frothy, foul-smelling discharge, itching and burning of the vulva, burning when passing urine and pain during intercourse. Small red spots on the cervix ("strawberry cervix") may be seen on examination.

Diagnosis

The preferred test is a nucleic acid amplification test (NAAT) on a vaginal swab or urine sample, which is highly sensitive. Moving parasites may be seen when discharge is examined under the microscope, but this method can miss a considerable proportion of infections. Women with trichomonas are also advised to be tested for chlamydia, gonorrhoea, syphilis and HIV.

Treatment and partner treatment

Treatment is with metronidazole or tinidazole. Current guidelines recommend a course of metronidazole lasting several days for women rather than a single dose, as this has been shown to be more effective. Partners must also be treated; otherwise the infection is passed back. You and your partner are advised to avoid sex until you have both finished treatment and symptoms have resolved. Because reinfection is common, women are advised to be retested within three months after treatment.

Trichomonas in pregnancy

In pregnancy, trichomoniasis has been linked to preterm birth, premature rupture of the membranes and low birth weight. Testing and treatment are recommended for pregnant women with symptoms; metronidazole can be used at any stage of pregnancy, while tinidazole is not preferred. For breastfeeding women, how treatment is given is planned with the doctor.

Other causes of discharge

• Inflammation of the cervix (cervicitis): sexually transmitted infections such as chlamydia and gonorrhoea can inflame the cervix and cause yellowish, pus-like discharge and bleeding after intercourse, although they often cause no symptoms at all. Untreated, they can spread to the uterus and tubes, leading to pelvic inflammatory disease, blocked tubes and a higher risk of ectopic pregnancy. Diagnosis is by NAAT, and partners also need treatment.
• Thinning of the vagina after menopause (atrophic vaginitis, genitourinary syndrome of menopause): low oestrogen can cause a small amount of watery or yellowish discharge, burning, dryness, pain during intercourse and urinary symptoms. Moisturisers, lubricants and, for suitable women, vaginal oestrogen reduce symptoms.
• Foreign body: a forgotten tampon, part of a condom or another object causes very foul-smelling, brownish discharge. Symptoms usually settle quickly once it is removed.
• Irritation and allergy: perfumed soaps, vaginal sprays, bubble baths, some pads and detergents, spermicides and latex can cause itching, burning and discharge.
• Cervical ectropion: cells that normally line the inside of the cervical canal are also present on its outer surface. It is common in young women, in pregnancy and with hormonal contraception. It can increase mucous discharge and cause spotting after intercourse. It is harmless and usually needs no treatment.
• Polyps and rarer causes: cervical polyps can increase discharge. Rarely, cancers of the cervix or uterus present with watery or bloody discharge.

An examination for discharge does not replace cervical screening (smear and/or HPV test). If your screening is not up to date, your doctor will plan the right time for it.

Prevention and daily care: common myths

• Do not douche. The vagina cleans itself. Douching reduces lactobacilli, is linked to a higher risk of bacterial vaginosis and pelvic inflammatory disease, and can temporarily mask discharge or odour, delaying diagnosis.
• Wash the vulva with water or a mild, unperfumed cleanser. Perfumed soaps, wet wipes, vaginal deodorants and bubble baths can cause irritation.
• Choose breathable cotton underwear and do not stay in a wet swimsuit or sweaty sportswear for long. Wearing panty liners all the time can increase moisture and irritation.
• Wipe from front to back after using the toilet.
• Use condoms. They protect against trichomonas, chlamydia and gonorrhoea and may also lower the risk of bacterial vaginosis.
• Avoid unnecessary antibiotics; if you often get thrush after antibiotics, tell your doctor. If you have diabetes, keeping blood sugar well controlled reduces recurrences.
• Use over-the-counter treatments with care. Pharmacy antifungal treatments are suitable only for women who have been diagnosed with thrush by a doctor before and have typical, identical symptoms. If you are unsure, if symptoms are different or if it is the first time, have an examination.
• Do not put yoghurt, vinegar, garlic or herbal mixtures in the vagina. No benefit has been shown and they can cause irritation. The role of probiotics in preventing or treating infections is not yet clear.

When should you see a doctor?

• Discharge with fever, chills or pelvic pain
• Grey, green, frothy or foul-smelling discharge
• Blood in the discharge, bleeding between periods or after intercourse
• Any bleeding or bloody discharge after menopause
• Pregnancy with a change in discharge, itching, leaking watery fluid or bleeding
• Symptoms for the first time, or different from what you have had before
• A new partner or concern about a sexually transmitted infection
• Symptoms that do not settle with treatment or return within two months
• Several infections within a year
• A suspected forgotten tampon or foreign body

Frequently Asked Questions

The information on this website is for general information only and does not replace a medical consultation.

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