The main causes of blood in the semen (termed as hematospermia) are as follows:
The other causes are:
An evaluation by a urologist would be prudent.
Read these resources;
Please feel free for your follow up questions.
No hemorrhoids cannot cause this. As I mentioned prostate would be the first organ to be screened. Prostatitis is the commonest cause. Getting a urine culture, sperm culture, digital rectal examination by your physician and later on may be an endoscopy will give the diagnosis of prostatitis. If this is ruled out then other causes are looked for.
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Best wishes and kindest regards.