The surface cells of the sheath of stallions and geldings produce lubricating mucus which, mixed with debris and shed cells, has a characteristic pasty consistency and a pungent odor. The material is known as smegma (from the Latin word for soap). The color of the smegma tends to be similar to the pigment color of the sheath skin in a particular horse. In most geldings and stallions, it is dark but pink skinned horses usually produce a reddish material. Some horses have more "productive" sheaths than others- they produce more smegma.