What is defined as the thickening of the epidermis due to friction or pressure?

The term that defines the thickening of the epidermis due to friction or pressure is callus. A callus forms as a protective response to repeated trauma or pressure on the skin, particularly on areas like the hands and feet. When the skin is subjected to consistent friction, the body increases the production of skin cells, resulting in a build-up of thickened skin. This phenomenon serves to protect the underlying tissues from damage.

In contrast, a blister is a fluid-filled sac that occurs as a result of friction or burns, while a wart is a growth caused by a viral infection, specifically the human papillomavirus (HPV). A fissure, on the other hand, refers to a crack or opening in the skin, often due to dryness or injury, rather than a response to friction or pressure. Understanding these distinctions helps in recognizing skin conditions and how they are formed.