Q. I noticed small streaks of blood in my semen. It happened once before, about one year ago. Do I have to worry about something serious, like cancer?

A. Seeing blood in the semen (hematospermia), even small streaks, can be alarming and make a man worry about cancer. However, rarely is cancer the cause.

Most commonly, bloody semen happens after a man has a medical procedure. Many men who have a prostate biopsy will have some blood in their semen for several days afterward. A cystoscopy (a catheter insertion through the urethra into the bladder) can also lead to temporary hematospermia, especially if the doctor takes biopsies of the bladder lining.

Since you have had only two episodes over a year, it's unlikely to represent a serious health issue. However, if you ejaculate during intercourse or oral sex without pulling out, you might not know if you have blood in your semen. In that case, my first recommendation would be to pull out before climax to be able to see the semen on at least several occasions. Assuming there are no other episodes, it's still a good idea to let your doctor know because physicians differ in how they approach this issue. Your doctor may want to perform a digital rectal exam to feel for hard or tender areas in the prostate and discuss prostate cancer screening with a PSA blood test (depending on your age). Repeated episodes of hematospermia should prompt a visit with a medical professional. Call your primary care provider first, as they may want you to see a urologist.

Even when bloody semen happens more than a couple of times, a specific reason often remains elusive. There's a long list of possible causes besides medical procedures. A man who has not ejaculated for a long time might notice bloody semen the next time he climaxes, probably related to swelling in the seminal vesicles from pent-up fluid. Also, men who ejaculate very frequently are more likely to have hematospermia. Other causes include

trauma to the genital area

acute or chronic prostatitis

benign prostatic hyperplasia (enlarged prostate)

bladder infection

sexually transmitted infections like gonorrhea and chlamydia

epididymitis (inflammation or infection in the small organ that collects and moves sperm from the testis to the sperm duct).

However, with most of these conditions, you would typically experience other symptoms, such as pain with urination or ejaculation, frequent urge to urinate, or penile discharge.

Image: © bluebay2014/Getty Images