Chlamydia and gonorrhea are the two sexually transmitted infections most commonly linked to blood in semen, a condition called hematospermia. Other STIs, including trichomoniasis and herpes, can also cause it. In men under 40, infection is the single most common reason blood shows up in semen.
Which STIs Cause Blood in Semen
Chlamydia and gonorrhea top the list because both infections target the urethra, prostate, and surrounding reproductive structures. When bacteria take hold in these tissues, inflammation damages small blood vessels, and that blood mixes into the semen during ejaculation. The prostate and seminal vesicles, which produce most of the fluid in semen, are especially vulnerable to this kind of inflammation.
Trichomoniasis, caused by a parasite rather than bacteria, can trigger the same inflammatory response in the urethra and prostate. Viral STIs like herpes and, in rarer cases, HIV or HPV can also contribute. Tuberculosis affecting the urinary tract is another infectious cause, though it’s uncommon in most Western countries.
How STIs Cause Bleeding
Semen passes through several structures on its way out of the body: the seminal vesicles, prostate gland, ejaculatory ducts, and urethra. An STI can inflame any of these. When tissue becomes inflamed, its blood vessels swell and become fragile. Even the normal pressure of ejaculation can rupture tiny vessels in irritated tissue, releasing blood into the semen.
Prostatitis (inflammation of the prostate) is one of the most frequent specific diagnoses behind hematospermia. STI-related prostatitis tends to be bacterial, but chronic cases can persist even after the initial infection clears, sometimes keeping blood in the semen for weeks. Inflammation of the seminal vesicles works the same way and is equally common as a source.
Other Symptoms That Point to an STI
Blood in semen on its own doesn’t confirm an STI. But if the cause is an infection, you’ll typically notice other symptoms alongside it. Pain or burning during urination is the most common companion sign. Unusual discharge from the penis, needing to urinate more frequently, and a dull ache in the lower abdomen or groin also suggest an infectious cause.
If the only symptom is a single episode of blood in semen with no pain, discharge, or urinary changes, an STI is less likely to be the explanation. That said, chlamydia in particular is known for producing mild or no obvious symptoms in many men, so testing is still worthwhile if you’ve had unprotected sex.
Non-STI Causes Worth Knowing
STIs aren’t the only reason blood appears in semen, and in many cases no clear cause is ever found. A long gap between ejaculations, vigorous or prolonged sexual activity, and frequent masturbation can all cause it without any infection being present. These cases are harmless and resolve on their own.
The most common categories of causes overall include:
- Infections: STIs, urinary tract infections, or bacterial prostatitis unrelated to an STI
- Inflammation: swelling of the prostate, seminal vesicles, or urethra without a specific infection
- Injury: trauma to the genitals, including from medical procedures like a prostate biopsy
- Structural problems: cysts, stones in the prostate or seminal vesicles, or blood vessel abnormalities
In men over 40, the list expands to include tumors, including prostate cancer, though this remains an uncommon cause. Hematospermia is most commonly secondary to an inflammatory or infectious cause and follows a benign, self-limited course.
When Age Changes the Picture
Age is the single biggest factor in how seriously blood in semen needs to be evaluated. In men under 40, infection accounts for the majority of cases. A single episode with no other symptoms often requires nothing more than a basic physical exam. If you’re sexually active with new or multiple partners, STI testing is a logical first step.
For men over 50, or men over 40 with a family history of prostate cancer, evaluation typically includes a prostate-specific antigen (PSA) test to screen for prostate cancer. African-American men in this age range face the same recommendation due to higher baseline prostate cancer risk. Blood in semen that persists for more than two months without a known cause, at any age, warrants more thorough investigation, potentially including imaging of the prostate and seminal vesicles.
Getting Tested and Treated
If you suspect an STI, the fastest path to an answer is a urine-based STI panel that screens for chlamydia and gonorrhea. Many clinics can run this test with results in a day or two. A urinalysis and urine culture can check for non-STI bacterial infections at the same time.
When an STI is confirmed, antibiotic treatment typically resolves both the infection and the bleeding. Chlamydia is commonly treated with a seven-day course of oral antibiotics. Gonorrhea treatment involves a different antibiotic regimen, usually a single injection. For infections involving the prostate, a course of antibiotics covering both common urinary bacteria and chlamydia is standard, often lasting one to two weeks.
After treatment begins, the blood in your semen won’t necessarily disappear immediately. Inflamed tissue needs time to heal, and residual blood can linger in the seminal vesicles for several ejaculations. Most men see the semen return to normal within a few weeks of completing treatment. If blood persists beyond two to three months after a confirmed infection has been cleared, further evaluation may be needed to rule out a structural or chronic inflammatory cause.