Having dark semen is a sign of blood mixing in with the semen. This condition is known as hematospermia. It has many possible causes, including urethral stricture and a prostate infection. In the majority of men, the cause is unknown and the condition clears on its own without explanation. Diagnosing the cause of dark semen requires a physical examination and medical tests performed by a urologist.
Dark semen, whether light tinges of color in otherwise healthy looking semen or semen that has undergone a complete color change, is due to hematospermia. Due to bleeding within the urinary or reproductive tracts, red blood cells are expelled through the urethra. Darker blood indicates that the blood originated from the testes or prostate, while lighter blood suggests a cut somewhere along the urethra. Many medical conditions can cause hematospermia and thus 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. Changes in semen color along with possible painful ejaculation appear shortly after this trauma. Though the cuts soon clot, the urethra becomes slightly narrower at the place where the bleeding occurred. The pressure of future ejaculation on this narrow area(s) can reopen wounds, leading to more bleeding.
Inflammation of the prostate can cause bleeding similar to that of a urethra stricture. In this case, infection or an undiagnosable reason causes minute bleeding. Blood originating from the prostate tends to make semen darker than blood from the urethra. This difference is due to how prostate blood, once released, has longer to oxidize before leaving the body. Like with urethra stricture, the severity of the cuts influence the degree to which semen color is affected.
For most men, dark semen is idiopathic, meaning the cause is unknown and/or undiagnosable. It occurs only once for no discernible reason and quickly disappears. If an individual should go to see a urologist, the urologist finds nothing wrong.
Even if dark semen is idiopathic, a man with this condition should consult a urologist to try to diagnose the underlying cause of hematospermia. After a general physical, a number of tests may be necessary to locate the point of bleeding. These tests can include prostate exam, ultrasound and/or inserting a fiber optic camera through the urethra. The latter is especially useful in diagnosing urethral strictures. Even if it is impossible to explain or stop episodes of bleeding, the patient will be able to understand how bleeding affects his overall health and reproductive capability.