Prostatitis: This is often the most common cause of blood in semen (hematospermia) due to inflammation of the prostate gland, which can lead to bleeding into the seminal fluid. Prostatitis can be acute or chronic and is usually caused by bacterial infection.

Benign Prostatic Hyperplasia (BPH): Enlargement of the prostate gland can cause bleeding into the semen due to the increased vascularity and potential for minor trauma during ejaculation.
Urethritis: Inflammation of the urethra can cause bleeding, which may then appear in the semen.
Seminal Vesiculitis: Inflammation of the seminal vesicles can lead to bleeding into the semen.

Prostate Cancer: Although less common, prostate cancer can cause hematospermia. It is crucial to rule out this potentially life-threatening condition.
Testicular Cancer: Though rare, testicular cancer can also present with hematospermia among other symptoms.
Urethral or Bladder Cancer: These cancers can also cause bleeding that appears in the semen.

Ejaculatory Duct Obstruction: This can cause hematospermia due to the potential for bleeding from the obstruction site.
Vascular Malformations: Rare vascular abnormalities in the genital area can cause bleeding into the semen.
Amyloidosis: A condition characterized by the deposition of amyloid (a protein) in various tissues, which can rarely cause hematospermia if it affects the genital or urinary tract.
Tuberculosis: Genitourinary tuberculosis is a rare condition in many parts of the world but can cause a variety of symptoms including hematospermia.