Several STIs can cause bleeding, with chlamydia and gonorrhea being the most common culprits. These two infections inflame the cervix, the lining of the uterus, or the rectum, which makes delicate tissue more likely to bleed during or after sex, between periods, or during bowel movements. But they’re not the only ones. Trichomoniasis, genital herpes, syphilis, HPV (genital warts), and a lesser-known infection called Mycoplasma genitalium can all cause bleeding in different ways.
Chlamydia and Gonorrhea
Chlamydia and gonorrhea are the STIs most strongly linked to abnormal bleeding, and they cause it through the same basic mechanism: inflammation. When either bacterium infects the cervix (cervicitis), the tissue becomes swollen, fragile, and prone to bleeding on contact. That’s why bleeding during or after sex is one of the hallmark signs. Spotting between periods or unusually heavy periods can also occur.
The tricky part is that both infections are frequently silent. Many people with chlamydia or gonorrhea have no symptoms at all, which is why routine screening is recommended for all sexually active women under 25 and for anyone with risk factors. When symptoms do appear, they often include unusual discharge, burning during urination, or that telltale spotting between periods.
Left untreated, either infection can spread deeper into the reproductive tract and cause pelvic inflammatory disease (PID), an infection of the uterus, fallopian tubes, or ovaries. PID commonly causes bleeding between periods alongside pelvic pain and foul-smelling discharge. Gonorrhea and chlamydia are the two most common causes of PID.
Trichomoniasis
Trichomoniasis is caused by a parasite rather than a bacterium, and it’s one of the most common curable STIs worldwide. It infects the vagina and can cause a yellow-green discharge, irritation, and a noticeable odor. Postcoital spotting, meaning light bleeding after sex, is a recognized symptom. Many women with trichomoniasis have no symptoms, so the infection can go undetected for weeks or months.
Mycoplasma Genitalium
Mycoplasma genitalium is an STI that doesn’t get nearly as much attention as chlamydia or gonorrhea, but it can cause similar problems. In a study of women diagnosed with Mycoplasma genitalium and PID, about 41% reported bleeding between periods, 46% had heavier-than-usual menstrual bleeding, and roughly 18% experienced bleeding during or after sex. Those numbers are comparable to what’s seen with better-known infections, yet many standard STI panels don’t test for it. If you’ve been treated for chlamydia and gonorrhea but your symptoms persist, Mycoplasma genitalium is worth asking about.
Genital Herpes
Herpes doesn’t cause the same kind of internal bleeding that chlamydia or gonorrhea do. Instead, the bleeding comes from the sores themselves. During an active outbreak, blisters form on the genitals or surrounding skin. When those blisters rupture, they turn into open ulcers that can ooze or bleed. If sores develop on the cervix or inside the vaginal canal, you might notice blood-tinged discharge or bleeding after sex without realizing the sores are there. Between outbreaks, herpes does not cause bleeding.
Syphilis
Primary syphilis produces a sore called a chancre at the site where the infection entered the body. That’s usually the genitals, anus, or mouth. A chancre is typically painless and firm, but it’s an open ulcer, so it can bleed when irritated by friction during sex or contact with clothing. Because chancres are painless and sometimes hidden inside the vagina or rectum, they’re easy to miss entirely. The sore heals on its own within a few weeks, but the infection progresses if untreated.
HPV and Genital Warts
Genital warts caused by HPV can bleed during sex, especially when they’re located in areas that experience friction. Warts on the vulva or inside the vaginal canal are most prone to this. The bleeding is usually minor and comes from the surface of the wart being stretched or rubbed. Not all HPV infections cause warts, and the strains that cause warts are different from the ones linked to cervical cancer, but any unexplained bleeding during sex is worth getting checked.
Rectal Bleeding From STIs
STI-related bleeding isn’t limited to vaginal bleeding. Anyone who has receptive anal sex can develop proctitis, which is inflammation of the rectum. The most common STI causes of proctitis are gonorrhea, chlamydia (especially a more aggressive form called LGV), herpes, and syphilis. Symptoms include rectal pain, discharge, a constant feeling of needing to have a bowel movement, and bleeding from the rectum. A specific type of chlamydia called lymphogranuloma venereum (LGV) is particularly associated with bloody rectal discharge and rectal ulcers.
How Bleeding Resolves With Treatment
For bacterial and parasitic STIs like chlamydia, gonorrhea, trichomoniasis, and Mycoplasma genitalium, antibiotics are the standard treatment. Most people start feeling better within a few days of beginning treatment, though you should avoid sexual contact until the full course is finished and your partner has been treated too. Bleeding caused by cervicitis or mild PID typically stops as the inflammation clears, which usually takes one to two weeks.
For herpes, antiviral medication shortens outbreaks and reduces their severity, which means sores heal faster and bleed less. Syphilis chancres also resolve after appropriate antibiotic treatment. Genital warts can be removed through several methods if they’re causing bleeding or discomfort, though the underlying HPV infection may persist.
The key pattern across all of these infections is that bleeding is a sign of tissue damage or inflammation. It’s your body telling you something is wrong with the surface of the cervix, the vaginal walls, the rectum, or the skin of the genitals. Because many of the STIs that cause bleeding are easily treatable but also easily missed, getting tested is the fastest path to an answer.