Why does a man bleed during sexual intercourse?

Patient's question:

Patient Age: 55 years old　　
Detailed Medical History and Purpose of Consultation: 20 years ago, during sexual activity with a partner, the patient experienced heavy bleeding and sought medical help from a local doctor (barefoot doctor) who prescribed medication. After that, everything returned to normal, and the patient had a son. To date, this has occurred three times, accompanied by symptoms of erectile dysfunction. The patient wants to consult about what the problem is and how to manage it.
Duration of Current Illness and Onset: July of this year (single episode of bleeding)
Current General Condition: Hasn't had sexual activity for a long time. Slightly underweight.

Doctor's answer:

Hello, blood in semen is called hematospermia. When the semen appears entirely light red or partially light red, or coffee-colored, it indicates the presence of blood, as normal semen should not contain blood components. The causes of hematospermia include:
(1) Inflammation of the reproductive tract, such as prostatitis, seminal vesiculitis, urethritis, epididymitis, prostatic calculi of the spermatic cord, or urethral-bladder calculi.
(2) Obstruction of the seminal tract and cysts.
(3) Tumors and vascular abnormalities.
(4) Systemic factors: hypertension, hemophilia.
(5) Trauma to the reproductive tract.
It is recommended that you visit a formal medical institution to identify the cause and avoid excessive sexual activity. Please seek medical attention at a formal hospital as soon as possible.