Semen consists of sperm and fluids released by the prostate and other glands. The fluids, also called ejaculate, join the sperm as they pass through a series of tubes to the urethra for ejaculation. A number of things can break blood vessels along this route or along the urinary route to the urethra. Broken vessels then leak blood into the semen, urine or both.

Your doctor will ask if you've had prostate surgery or a prostate biopsy recently, since these procedures can cause blood in semen for several weeks afterward.

Most often, no cause can be found for blood in semen. In some cases, particularly among men under age 40, infection is a possible cause. Infection is usually accompanied by other signs and symptoms, such as painful urination.

For men age 40 and older, or if the blood in semen is severe or recurrent, in rare cases this might be a warning sign for conditions such as cancer. As a result, a more-careful evaluation might be needed. But the risk is low. In a follow-up study of 200 men, mostly over 40, who typically had multiple episodes of blood in their semen, prostate cancer developed in only 4 percent.

Possible causes of blood in semen:
Brachytherapy
Chlamydia trachomatis
Epididymitis (testicle inflammation)
External beam radiation for prostate cancer
Gonorrhea
Genital herpes
Hemophilia
Interrupted sex
Orchitis (inflamed testicle)
Prolonged sexual abstinence
Prostate biopsy
Prostate cancer
Prostatitis (infection or inflammation of the prostate)
Testicular trauma
Vasectomy
Excessive sexual activity or masturbation