Original: Its cause could be the result of inflammation, infection, blockage, or injury of the male reproductive tract or a problem within the urethra, testicles, epididymis and prostate.
Simplified: This is a condition called hematospermia, and may be due to some blockage, inflammation, infection or injury to some part of the male sex organs, such as the urethra, epididymis, prostate or testicles.