Immunological Defense: The mucous membranes that line all body orifices are the body's first line of immunological defense. Glands in the foreskin produce antibacterial and antiviral proteins such as lysozyme, which is found in tears and in mother's milk. Specialized immune system components abound in the foreskin's outer surface. Plasma cells in the foreskin's mucosal lining secrete immunoglobulins -- antibodies that defend against infection.
Erogenous Sensitivity: The foreskin is as sensitive as the fingertips or the lips of the mouth. It contains a richer variety and greater concentration of specialized nerve receptors than any other part of the penis. These specialized nerve endings can discern motion, subtle changes in temperature and fine gradations of texture.
Coverage during Erection: As it becomes erect, the penile shaft becomes thicker and longer. The double-layered foreskin provides the skin necessary to accommodate the expanded organ and to allow the penile skin to glide freely, smoothly, and pleasurably over the shaft and glans.
Self-Stimulating Sexual Functions: The foreskin's double-layered sheath enables the penile shaft skin to glide back and forth over the penile shaft. The foreskin can normally be slipped all or partially back to the base of the penis, and can also slip forward beyond the glans. This wide range of motion is the mechanism by which the penis and the orgasmic triggers in the foreskin, frenulum and glans are stimulated.