If your semen is red or reddish-brown, it's possible that you might have a sexually transmitted infection like chlamydia, herpes, or gonorrhea. Infections can irritate the lining of your urinary tract, prostate, or testicles, which can cause bleeding, creating red streaks or a reddish brown tint, Dr. Brahmbhatt explains.

There’s also a chance that bacteria or a virus from an infection could give your semen a greenish tint or foul smell. Usually, greenish semen indicates a prostate infection—but it’s pretty rare. “In my 10 years as a urologist I’ve never seen this,” Dr. Brahmbhatt says. “But that doesn’t mean it can’t happen.”

Either way, you should call the doctor as soon as possible if you suspect that you have an infection. (You might also notice other symptoms of STIs, like painful urination.)