: calluses) is an area of thickened and sometimes hardened skin that forms as a response to repeated friction, pressure, or other irritation.

Normally, a callus will form on any part of the skin exposed to excess friction over a long period of time.

On the feet (arguably the source of the most problematic calluses), they typically form on the metatarsal-phalangeal joint area ("balls of the foot"), heels and small toes due to the compression applied by tightly fitting shoes.

Though the cells of calluses are dead, they are quite resistant to mechanical and chemical damage due to extensive networks of cross-linked proteins and hydrophobic keratin intermediate filaments containing many disulfide bonds.

There is a benign condition called keratosis palmaris et plantaris, which produces corns in the creases of the fingers and non-weight bearing spaces of the feet.

A corn (or clavus, plural clavi) is a cone-shaped callus that penetrates into the dermis, usually on the feet or hands.

[1] The hard part at the center of the corn resembles a funnel with a broad raised top and a pointed bottom.

People with poor circulation or sensation should check their skin often for signs of rubbing and irritation so they can minimize any damage.

They may also be dissolved with keratolytic agents containing salicylic acid, sanded down with a pumice stone or silicon carbide sandpaper or filed down with a callus shaver, or pared down by a professional such as a podiatrist.

[14][15][16] During the Gads Hill Train Robbery in 1874, the James–Younger Gang purportedly refrained from robbing men with calloused hands, assuming them to be working class laborers.

[17][18] Such notion is also present in Māori culture, where the words raupā and raupo refer to hands left cracked and chapped due to manual work, and are used as similes for someone deemed a hard worker.