The penis, the outer reproductive organ of the male, consists of two parts -- the shaft and the glans. The glans is the tip of the penis, while the shaft is the main part of the penis. All boys are born with a foreskin, or a covering over the tip of the penis. The foreskin acts as a covering to protect the delicate glans underneath. When a boy is circumcised, this protective foreskin is lost.

Skin cells from the glans of the penis and the inner lining of the foreskin are shed throughout life. Since this shedding takes place in a closed space, they will work their way to the tip of the foreskin. These skin cells are called smegma.