Several sexually transmitted infections cause unusual discharge, most commonly chlamydia, gonorrhea, and trichomoniasis. Each produces discharge with slightly different characteristics, and knowing what to look for can help you recognize a potential infection early. That said, many STIs produce no symptoms at all, so discharge alone isn’t a reliable way to rule an infection in or out.
Chlamydia
Chlamydia is one of the most common STIs worldwide, yet roughly 77% of all chlamydia cases never produce symptoms. When discharge does appear, it typically shows up one to three weeks after exposure. In women, chlamydia discharge is usually thin, white, or slightly cloudy. In men, it tends to be a clear or whitish fluid from the tip of the penis, often most noticeable in the morning.
Because chlamydia so often flies under the radar, routine screening is the main way infections get caught. Left untreated, chlamydia can spread deeper into the reproductive tract in women, potentially leading to pelvic inflammatory disease, which produces heavier, foul-smelling discharge along with pelvic pain and fever. In men, untreated chlamydia can cause painful swelling in the testicles.
Gonorrhea
Gonorrhea tends to produce more obvious discharge than chlamydia, especially in men. Penile discharge from gonorrhea is often thick, yellow or green, and can appear as early as two to five days after exposure. It’s sometimes described as looking like pus, and it may stain underwear noticeably.
In women, gonorrhea discharge can be yellow or greenish, but it’s frequently mild enough to be mistaken for normal vaginal fluid. About 45% of gonorrhea cases never cause symptoms, so even a “normal-looking” discharge doesn’t guarantee you’re in the clear. Painful urination often accompanies the discharge in both men and women, and the combination of the two is a strong signal to get tested.
Trichomoniasis
Trichomoniasis, caused by a parasite rather than bacteria, is especially common in women and produces some of the most distinctive discharge of any STI. The discharge is thin, frothy, and ranges from clear to white, yellowish, or greenish. A strong fishy odor is the hallmark. Symptoms usually develop within one to four weeks of exposure, though many people remain asymptomatic for months or even longer.
Women with trichomoniasis often experience genital redness, soreness, burning, and discomfort while urinating alongside the discharge. During a clinical exam, about 40% of women with trich show a characteristic “strawberry cervix,” where tiny red spots appear on the cervix from inflammation. Men with trichomoniasis rarely notice symptoms, though some develop mild penile discharge or irritation.
Mycoplasma Genitalium
Mycoplasma genitalium is a lesser-known bacterial STI that’s increasingly recognized as a cause of unexplained discharge. In women, it can produce vaginal discharge that may have an unpleasant smell. In men, it typically causes a thin, clear or slightly cloudy penile discharge similar to what chlamydia produces. Because standard STI panels don’t always test for it, mycoplasma genitalium is easy to miss. If you’ve been treated for chlamydia or gonorrhea but your symptoms haven’t cleared, this infection is worth asking about.
How STI Discharge Differs From Other Causes
Not all unusual discharge comes from an STI. Bacterial vaginosis (BV) is one of the most common reasons women develop a thin, grayish discharge with a fishy smell, and it’s not sexually transmitted. BV happens when the natural balance of bacteria in the vagina shifts, raising the vaginal pH. Clinicians can often distinguish BV from STI-related discharge using a simple pH test or by checking for a fishy odor when a chemical is added to a sample (known as the whiff test). Yeast infections, which produce thick, white, cottage cheese-like discharge without much odor, are another frequent non-STI cause.
The tricky part is that BV, yeast infections, and STIs can all coexist, and their symptoms overlap enough that self-diagnosis is unreliable. Color, smell, and consistency offer clues, but testing is the only way to know for certain what’s causing the problem.
What Discharge Looks Like in Men
Penile discharge from an STI falls into a rough spectrum. Gonorrhea sits at one end with thick, yellow-green, pus-like fluid. At the other end, non-gonococcal urethritis (often caused by chlamydia or mycoplasma genitalium) produces discharge that’s clear, whitish, or slightly mucus-like. Some men notice only a small amount of fluid at the urethral opening, while others see enough to stain clothing. Itching or burning at the tip of the penis and pain during urination are common companions regardless of the specific infection.
Why Symptoms Alone Aren’t Enough
The single most important thing to understand about STI-related discharge is that its absence means very little. Research estimates that 95% of untreated chlamydia cases and 86% of untreated gonorrhea cases go undiagnosed specifically because the infected person never develops symptoms. This is why screening matters even when everything looks and feels normal, particularly if you’ve had unprotected sex or a new partner.
When testing is done, the standard method uses a swab or urine sample analyzed through nucleic acid amplification testing (NAAT), which detects genetic material from the bacteria or parasite. These tests are highly accurate, with sensitivity above 90% and specificity around 98%. Results typically come back within three to five days, though some clinics offer rapid point-of-care options.
What to Expect From Treatment
The good news is that chlamydia, gonorrhea, and trichomoniasis are all curable with antibiotics. Chlamydia is treated with a week-long course of oral antibiotics. Gonorrhea requires an antibiotic injection. Trichomoniasis is cleared with a single oral dose of antiparasitic medication in most cases. Mycoplasma genitalium can be harder to treat because some strains have developed resistance, but targeted antibiotics are available.
Discharge typically starts to improve within a few days of beginning treatment, though you should avoid sexual contact until the full course is complete and any sexual partners have been treated as well. Reinfection is common, especially with chlamydia and gonorrhea, so follow-up testing about three months after treatment is a standard recommendation.