Sole (foot anatomy)

The sole, also known as the plantar surface, is the lower side of the foot of humans and walking animals. It is the part of the skin or shoe that makes contact with the ground when a person stands or walks. In Somali, the term 'raad' also refers to the mark or impression that the foot leaves on soft ground, such as sand or mud.

The sole has a distinctive structure that distributes the body's weight across different areas. Most of the weight is borne by the heel (calcaneus) and the ball of the foot, while the middle inner section is typically a hollow area that normally does not make full contact with the ground.

Anatomy of the skin

The skin of the sole differs from skin elsewhere on the body. It is extremely thick and has deep ridges (the upper layer of skin is notably thick), and it has no hair. It contains numerous sweat glands, which is why the sole often perspires. The sole also has distinctive ridge patterns unique to each person, similar to fingerprints, which can be used for personal identification.

Soft tissue and muscles

Under the skin lies a soft cushioning layer that functions as a shock absorber, particularly under the heel and ball of the foot. There is also a strong fibrous band (plantar fascia) that runs from the heel to the toes and supports the arch of the foot. Small muscles and tendons in the sole assist with movement and coordination of the foot.

Sensation and function

The sole is highly sensitive: it senses pressure, touch, temperature, and pain. Information from the sole helps the brain maintain balance and control movement. For this reason, the sole is extremely sensitive to stimulation, and tickling the sole often produces a rapid reflex response in many people.

Common health conditions

Plantar fasciitis (inflammation and pain arising from the plantar fascia) is one of the most commonly encountered conditions, with characteristic heel pain that is typically worse in the morning. Other conditions include corns and calluses, athlete's foot fungal infection, and fungal diseases. Elderly people or those with diabetes may develop serious foot sores because sensation in the foot may be reduced.