Having recent prostate surgery or a prostate biopsy can cause blood in semen for several weeks after the procedure.

Most often, no cause can be found for blood in semen. Infection might be a cause. But infection is likely to have other symptoms. These may include pain while urinating or urinating more often.

A lot of blood in semen or blood that keeps coming back might be a warning sign for conditions such as cancer. But this is rare.

Possible causes of blood in semen:

• A lot of sexual activity or masturbation.
• Blood vessel malformation, a tangle of blood vessels that disrupts blood flow.
• Conditions that cause the urinary or reproductive organs to become inflamed.
• Infections of the urinary or reproductive organs from germs or fungus.
• Not having sex for a long time.
• Radiation therapy to the pelvis.
• Recent urological procedures, such as a bladder scope, prostate biopsy or vasectomy.
• Trauma to the pelvis or genitals.
• Side effects of medicines that thin the blood, such as warfarin.

If you see blood in your semen, it's likely to clear up without treatment. However, it's a good idea to make an appointment with a healthcare professional. A physical exam and simple blood or urine tests are often all that is necessary to identify or rule out many causes, such as infections.

If you have certain risk factors and symptoms, you might need more testing to rule out a more serious condition. Call your healthcare professional about blood in semen if you:

• Have blood in semen that lasts longer than 3 to 4 weeks.
• Keep seeing blood in semen.
• Have other symptoms, such as pain while urinating or pain with ejaculation.
• Have other risk factors such as having a history of cancer, bleeding conditions or having recently had sex that puts you at risk of sexually transmitted infections.