Blood in the semen, called hematospermia, is blood that is either too small to be seen (microscopic) or visible in the ejaculation fluid.

For men under age 40, infection is the most common cause. Infection is usually accompanied by other signs and symptoms, such as fever, genital or urinary pain, difficulty urinating, or blood in your urine.

For men age 40 and older, blood in semen is a slight predictor of a cancer (malignancy), most often prostate cancer. So a more careful evaluation is merited when this sign appears in this age group. But the risk is low. In follow-up studies of more than 800 men who had blood in their semen, cancer was found in less than 4 percent (on average).

Symptoms that may occur with this condition include:
Blood in urine
Fever or chills
Lower back pain
Pain with bowel movement
Pain with ejaculation
Pain with urination
Swelling in scrotum
Swelling or tenderness in groin area
Tenderness in the scrotum

More common causes of blood in semen:
Brachytherapy
Chlamydia
Epididymitis
Genital herpes
Gonorrhea
Interrupted sex
Prolonged sexual abstinence
Prostate biopsy
Prostate gland enlargement
Prostatitis
Seminal vesiculitis
Testicular trauma
Vasectomy: An effective form of male birth control
Vigorous sex
Less common causes:
Amyloidosis
Benign growths (cysts, polyps) in the bladder, urethra or prostate
Bladder cancer
Fragile blood vessels
Hemophilia
Prostate cancer
Schistosomiasis
Testicular cancer
Thrombocytopenia (low platelet count)
Tuberculosis
Von Willebrand disease
Warfarin side effects: Watch for interactions