There is no need for the foreskin to be retractable until puberty. Only then are humans biologically programmed to become sexually mature. In babies and young children, the natural attachment of the foreskin to the glans protects the immature glans from injury and dirt. The firmly attached foreskin provides a natural protective barrier for the urinary tract. This is especially important in infancy and during the diaper-wearing years. Of equal importance, the attachment of the foreskin to the glans protects and preserves the head of the penis, allowing it to complete its development.