Several sexually transmitted infections cause abnormal discharge, including chlamydia, gonorrhea, trichomoniasis, and mycoplasma genitalium. Each produces discharge with somewhat different characteristics, though there’s enough overlap that appearance alone can’t reliably identify the cause. Here’s what to know about each one, how they differ, and how they compare to non-STI infections that also change your discharge.
Gonorrhea
Gonorrhea is one of the most recognizable STIs when it comes to discharge, particularly in men. Penile discharge from gonorrhea is typically white, yellow, or green, and it can have a noticeable smell. Symptoms usually show up within 2 to 8 days of exposure, though it can take up to two weeks. In 2024, over 543,000 gonorrhea cases were reported in the United States.
In women, gonorrhea causes increased vaginal discharge, but it’s harder to distinguish from normal vaginal fluid. Women are also more likely to have no symptoms at all, which is one reason gonorrhea often goes undiagnosed. Rectal infections in any gender can also produce discharge, sometimes with no other symptoms.
Chlamydia
Chlamydia is the most commonly reported STI in the U.S., with roughly 1.5 million cases in 2024. It causes discharge from the vagina, penis, or rectum, but the discharge tends to be less dramatic than gonorrhea. In men, it’s often a mild, clear or whitish fluid from the penis. In women, the change in vaginal discharge can be subtle enough to miss entirely.
Symptoms typically appear 1 to 3 weeks after exposure, but the bigger issue with chlamydia is that many people never develop noticeable symptoms. Up to 70% of women and about half of men with chlamydia are asymptomatic. That’s why routine screening matters even if your discharge seems normal. Chlamydia also accounts for a significant share of inflammation in the cervix, which can cause discharge mixed with blood, particularly after sex.
Trichomoniasis
Trichomoniasis produces the most distinctive discharge of the common STIs. In women, the discharge is typically thin or frothy with a foul smell, and it can be clear, white, yellow, or green. The frothy texture is a hallmark that sets it apart from other infections. Symptoms appear anywhere from 5 to 28 days after exposure.
Trichomoniasis is caused by a parasite rather than a bacterium, and it primarily affects women. Men can carry and transmit it, but they rarely develop significant discharge. When men do have symptoms, it’s usually mild irritation or a slight discharge from the penis. This infection is extremely common, though it’s often underdiagnosed because it isn’t included in standard STI panels unless specifically requested.
Mycoplasma Genitalium
Mycoplasma genitalium is a lesser-known STI that’s increasingly recognized as a cause of abnormal discharge. It’s responsible for an estimated 15% to 25% of non-gonococcal urethritis cases in men, meaning it causes urethral inflammation and discharge when gonorrhea isn’t the culprit. The discharge is usually mild and may come with burning during urination or irritation at the tip of the penis.
In women, mycoplasma genitalium can inflame the cervix, potentially causing abnormal vaginal discharge and bleeding between periods or after intercourse. Like chlamydia, it’s frequently asymptomatic, which makes it easy to overlook. Testing for this infection has become more widely available in recent years, but it still isn’t part of a routine STI screening at most clinics, so you may need to ask for it specifically.
How STI Discharge Differs From Other Infections
Not all abnormal discharge comes from an STI. Two of the most common non-STI vaginal infections, yeast infections and bacterial vaginosis (BV), also change your discharge in distinct ways.
- Yeast infections produce thick, white, clumpy discharge often described as looking like cottage cheese. It’s usually odorless. The main symptom is intense itching rather than a change in smell.
- Bacterial vaginosis causes thin, watery, grayish-white discharge with a strong fishy odor that often becomes more noticeable after sex. BV raises vaginal pH, while yeast infections typically don’t.
- STI-related discharge varies more widely. Gonorrhea can be thick and colored. Trichomoniasis is frothy and foul-smelling. Chlamydia and mycoplasma genitalium may cause only subtle changes. Burning with urination, bleeding between periods, or discharge from the rectum all point more toward an STI than a yeast infection or BV.
The overlap between these conditions is real. Trichomoniasis and BV can both produce a fishy odor. Chlamydia discharge can look a lot like early BV. You can also have more than one infection at the same time. Color and smell give you clues, but they aren’t a reliable way to self-diagnose.
Why Discharge Alone Isn’t Enough for Diagnosis
The most accurate way to identify the cause of abnormal discharge is a nucleic acid amplification test, which detects the genetic material of the infection. These tests have sensitivity above 90% and specificity above 99%, meaning they’re highly reliable. They can identify chlamydia, gonorrhea, trichomoniasis, and mycoplasma genitalium from a urine sample or a swab.
This matters because so many of these infections look similar on the surface, and because some cause no visible discharge at all. If you’re noticing new or changed discharge, especially if it’s accompanied by an unusual smell, pain during urination, or bleeding between periods, getting tested is the fastest path to a clear answer. Most results come back within a few days, and all four of the infections discussed here are treatable.
How Symptoms Differ by Anatomy
The same infection can look quite different depending on your anatomy. In people with a penis, STI-related discharge tends to be more obvious because any fluid coming from the urethra outside of urination is abnormal. Gonorrhea in particular often produces a visibly colored, thick discharge that’s hard to ignore.
In people with a vagina, distinguishing STI discharge from normal vaginal fluid is trickier. The vagina naturally produces discharge that changes throughout the menstrual cycle. STIs that infect the cervix, like chlamydia and mycoplasma genitalium, may cause only a slight increase in discharge or a change in color. Bleeding after sex or between periods is sometimes the more noticeable sign. Rectal infections from chlamydia or gonorrhea can cause discharge or bleeding regardless of anatomy, and they’re often completely silent.