The glans, or head of the penis, is not made of normal skin like your face or your hands. It is actually a mucous membrane like the eyeball. Circumcision removes the body's natural protection for this mucous membrane. That natural covering is the foreskin, which acts somewhat like an eyelid, cleaning, protecting and keeping the glans moist. In its natural, unaltered state, the surface of the glans is very thin, barely more than one cell thick, exposing the nerve endings there, and making the glans extremely sensitive to touch, temperature, etc. Without a foreskin to protect it, the glans dries out and is exposed to irritation from clothing and enviromental contaminants. The body reacts by forming a thick covering over the glans to protect it from exposure. The surface thickens, shielding you from constant irritation and pain, but also deadening the feelings of the sensitive organ. This thickening is called keratinization. After doing foreskin restoration for a while, the outer layers of this thickened skin begin to slough away, bringing the nerve endings back to the surface. The keratinized tissue looks like dried skin when it comes away, like a sunburn. The sensitivity of your penis after this happens is incredible. It is like having a brand new dick.