Grey discharge from the vagina is almost always a sign of bacterial vaginosis (BV), the most common vaginal infection in women of reproductive age. It typically appears thin and milky, coats the vaginal walls evenly, and often comes with a noticeable fishy smell. BV affects roughly 23 to 29 percent of reproductive-age women worldwide, so while it can be alarming to notice, it’s extremely common and treatable.
What Grey Discharge Looks and Smells Like
The discharge from BV is thin, with a milk-like consistency that spreads smoothly rather than clumping. Its color ranges from white-grey to yellow-green, and it can be heavier than your normal discharge. The hallmark feature is the odor: a strong fishy smell caused by chemical compounds (putrescine, cadaverine, and trimethylamine) produced by the overgrown bacteria. The smell often becomes more noticeable after sex or during your period.
Some women also experience mild itching or burning around the vulva, though BV is far less irritating than yeast infections or other vaginal infections. Many women with BV have no symptoms at all beyond the change in discharge.
Why It Happens
Your vagina naturally maintains a balance of bacteria, dominated by protective species that keep the environment slightly acidic. BV develops when that balance tips: protective bacteria decline, and a diverse mix of other bacteria overgrows. This raises vaginal pH above 4.5, creating the conditions for grey discharge and odor.
Several things can trigger this shift:
- Douching is the most well-established disruptor. It washes away protective bacteria and directly predisposes you to BV and other infections.
- A new sexual partner or multiple partners can introduce bacteria that alter the vaginal environment. BV isn’t classified as a sexually transmitted infection, but sexual activity is a consistent risk factor.
- Smoking has anti-estrogen effects that suppress protective bacterial growth. A chemical found in cigarette smoke has actually been detected in vaginal secretions of smokers.
- Stress plays a measurable role. Women reporting moderate to high stress levels are roughly twice as likely to develop BV compared to women with low stress.
- Menstruation temporarily shifts your vaginal bacteria each cycle. The pH rises during your period, and protective bacteria decline, which is why some women notice symptoms flare around that time.
- Diet and weight also matter. Low intake of vitamins E, folate, and calcium has been linked to higher BV risk, while obesity is associated with less protective vaginal bacteria overall.
Hormonal changes near menopause can cause a similar shift as estrogen levels drop, making BV more likely in perimenopause as well.
How BV Is Different From Other Infections
Grey discharge can look similar to other vaginal infections at first glance, but there are key differences. A yeast infection produces thick, white, clumpy discharge (often compared to cottage cheese) with intense itching but usually no odor. BV discharge is thin and uniform with a strong smell but relatively little irritation.
Trichomoniasis, a sexually transmitted infection, can also cause a change in discharge, sometimes with a fishy smell. But trichomoniasis tends to produce more redness, soreness, and burning in the genital area. The discharge may appear frothy or greenish-yellow rather than the smooth, grey coating typical of BV. Because these infections can overlap in symptoms, testing is the only reliable way to tell them apart.
How It’s Diagnosed
A clinician can usually diagnose BV during a standard pelvic exam. They look for three of four specific signs: the characteristic thin, homogeneous discharge; a vaginal pH above 4.5; a fishy odor when a small chemical is added to a sample of the discharge; and the presence of “clue cells” under a microscope, which are vaginal cells coated in a visible layer of bacteria. The exam is quick and straightforward.
Treatment and What to Expect
BV is treated with antibiotics, available either as oral pills or a vaginal gel or cream. Most treatment courses last five to seven days. Symptoms typically improve within a few days of starting treatment, though you should finish the full course even after the discharge clears.
The frustrating part of BV is that it recurs frequently. Many women experience repeat episodes within months of successful treatment. Avoiding douching, reducing vaginal irritants, and maintaining overall health (managing stress, not smoking) can help lower the odds of recurrence, though no prevention strategy is guaranteed.
Risks of Leaving It Untreated
BV isn’t just a nuisance. Left untreated, the bacterial overgrowth can increase your vulnerability to sexually transmitted infections, including HIV, because the loss of protective bacteria weakens one of the body’s natural barriers.
During pregnancy, BV carries more serious concerns. A meta-analysis of over 50,000 patients found that BV during pregnancy was associated with a 60 percent higher likelihood of preterm birth. The leading theory is that bacteria can travel upward from the vagina to the fetal membranes, potentially triggering early labor or premature rupture of membranes. Interestingly, studies have not yet shown that treating BV with antibiotics during pregnancy reliably reduces preterm birth risk, which remains an active question in obstetric care.
BV can also increase the risk of infection after gynecological procedures like IUD insertion or surgery, so it’s worth addressing before any planned procedures.