Blood in semen is when the semen or ejaculate turns a red-pink or brown colour after sex or masturbation. There are a number of causes of blood ending up in the semen, or heamatospermia, as it's medically termed. Although it can be quite alarming to find blood in your ejaculate, it is usually not anything to worry about and clears up by itself without any treatment.
Blood in the semen can be caused by inflammation, injury or infection in the reproductive system. Inflammation of the glands (seminal vesicles) that produce a lot of the fluid in semen is called vesiculitis, small stones in this area can also cause blood in the semen. Inflammation of the prostate gland (where semen is produced) called prostatitis, recent surgery on any part of the urinary and reproductive system such as the bladder or prostate as well as sexually transmitted infections (STIs) can lead to blood in the semen. Less common but more concerning conditions that may cause haematospermia include an inability of your blood to form clots properly, cancer of any part of the urinary and reproductive system, and severe high blood pressure.
Blood in your semen is reason to see your doctor, usually in a routine appointment. They are the best person to discuss what is the most likely cause, and decide any further investigations to determine the cause, or any treatment needed.
Your doctor will take a thorough history from you, including recent sexual contacts or infections, and they will need to check your blood pressure, examine your tummy, genitals and prostate gland (this is done by inserting a finger into your back passage). They may ask you to provide a urine sample to rule out a urine infection or STI, and it will analyse if there is blood in the urine. If your doctor has any concerns, they will refer you to a specialist doctor called a urologist for further review.
Any treatment depends on the cause. Generally, most things will improve by themselves without any intervention, some may require antibiotics or anti-inflammatory medication. If the underlying cause is concerning, your doctor will refer you to a specialist for appropriate treatment. If the underlying cause is due to an STI, then it is likely to be infectious and can pass onto a sexual partner through sexual intercourse until you have both been fully treated.