Having dark semen is a sign of blood mixing with semen. This condition is known as hematospermia. It has many possible causes, including urethral stricture and prostate infection. In most men, the cause is unknown and the condition goes away on its own without explanation. Diagnosing the cause of dark semen requires a physical exam and medical tests performed by a urologist.
Dark semen, whether it's a slight tinge of color in healthy-looking semen or semen that has undergone a complete color change, is due to hematospermia. Due to bleeding within the urinary or reproductive tract, red blood cells are expelled through the urethra. Darker blood indicates that the blood originated in the testicles or prostate, while lighter blood suggests a cut somewhere along the urethra. Many medical conditions can cause hematospermia and therefore dark semen.
Physical trauma to the urethra can cause urethral stricture and dark semen. Vigorous sexual activity or accidental injury creates micro tears along the urethra, causing bleeding. Dark semen along with possible painful ejaculation appear soon after this trauma. Although the cuts soon coagulate, the urethra becomes slightly narrower at the site of the bleeding. The pressure of future ejaculate on this narrow area(s) can reopen wounds and lead to more bleeding.
Inflammation of the prostate can cause bleeding similar to that of stricture of the urethra. In this case, infection or an undiagnosable reason causes minute bleeding. Blood originating from the prostate tends to darken semen than blood from the urethra. This difference is due to how blood from the prostate, once released, has more time to oxidize before leaving the body. As with urethral stricture, the severity of the cuts influences the degree to which semen color is affected.
For most men, dark semen is idiopathic, meaning the cause is unknown and/or undiagnosable. It happens only once for no apparent reason and goes away quickly. If an individual must go to see a urologist, the urologist finds nothing wrong.
Even if dark semen is idiopathic, a man with this condition should see a urologist to try to diagnose the underlying cause of hematospermia. After a general physical exam, several tests may be necessary to locate the bleeding point. These tests may include prostate exam, ultrasound, and/or insertion of a fiber optic camera through the urethra. The latter is especially useful in the diagnosis of urethral strictures. Even if it is impossible to explain or stop the bleeding episodes, the patient will be able to understand how the bleeding affects their general health and reproductive capacity.