Prostatitis: This is often the most common cause of bloody semen (hematospermia) in young men. Prostatitis, especially chronic prostatitis, can lead to inflammation of the prostate gland, which may result in bleeding into the semen.

Urethritis: Inflammation of the urethra, often due to infection, can cause bleeding that mixes with semen.
Seminal Vesiculitis: Inflammation of the seminal vesicles, which can be due to infection or other causes, may lead to bloody semen.
Ejaculatory Duct Obstruction: Blockage of the ejaculatory ducts can cause bleeding due to the increased pressure and potential rupture of the ducts.

Prostate Cancer: Although less common in younger men, prostate cancer can cause hematospermia. It is crucial to rule out this potentially life-threatening condition.
Testicular Cancer: Though rare, testicular cancer can metastasize and cause secondary effects leading to hematospermia.
Trauma: Physical trauma to the genital area can cause internal bleeding that may result in bloody semen.

Amyloidosis: A condition characterized by the deposition of amyloid proteins in various tissues, including the prostate and seminal vesicles, which can lead to bleeding.
Vascular Malformations: Abnormal formations of blood vessels in the genital area can cause bleeding into the semen.
Infections like Tuberculosis: Genitourinary tuberculosis is a rare condition in many parts of the world but can cause a variety of symptoms, including hematospermia.
Benign Prostatic Hyperplasia (BPH): Although more common in older men, BPH can occasionally cause hematospermia due to the enlargement of the prostate gland.