Sole (foot)

Overview
The sole is the bottom of the human foot. Anatomically, the sole of the foot is referred to as the plantar aspect. The equivalent surface in ungulates is the hoof.

Description
The skin on the sole of the foot lacks the vellus hair and pigmentation found on the rest of the body, and has a high concentration of sweat pores. The soles are crossed by a set of creases that form during embryogenesis and contain the thickest layers of skin on the human body due to the weight that is continually placed on them. Like the palm, the sweat pores of the sole lack sebaceous glands.

Innervation of the sole
The soles of the feet are extremely sensitive to touch due to a high concentration of nerve endings. This makes them sensitive to surfaces that are walked on, ticklish and some people find them to be erogenous zones. Medically, the soles are the site of the plantar reflex, the testing of which can be painful due to the sole's sensitivity. The feet can also be a used for torture.

Arches
The sole of the adult foot is normally arched. Arches may fail to develop during childhood or may flatten during pregnancy and old age resulting in flat feet.

The sole of the foot in culture
In the Middle East the sole of the foot is considered unclean and it is considered insulting or offensive to prominently display a barefoot. In Western culture the sensitivity of the sole makes it a target for tickling or sexual stimulation.