During an erection, the penis often produces a small amount of clear fluid, called pre-ejaculate (or "pre-cum"). The purpose of pre-cum is to clean the urethra--the tube that carries urine and semen--and to help sperm stay alive as they travel through the vagina. Because pre-cum travels through the urethra, it can pickup leftover sperm from a previous ejaculation, and therefore can cause pregnancy if it gets inside a woman's vagina (even just at the opening). Pre-cum can also carry sexually transmitted diseases.
During an erection, the penis often produces a small amount of clear fluid, called pre-ejaculate (or "pre-cum"). The purpose of pre-cum is to clean the urethra--the tube that carries urine and semen--and to help sperm stay alive as they travel through the vagina. Because pre-cum travels through the urethra, it can pickup leftover sperm from a previous ejaculation, and therefore can cause pregnancy if it gets inside a woman's vagina (even just at the opening). Pre-cum can also carry 
