Which layer of skin is visible externally?

The epidermis is the outermost layer of the skin and is the part that is visible externally. It serves as the body's first line of defense against environmental elements such as pathogens, chemicals, and physical injuries. The epidermis is primarily composed of keratinized stratified squamous epithelium, which helps protect underlying tissues and prevent water loss. This layer contains skin cells that constantly shed and are replaced, revealing the new cells underneath.

In contrast, the dermis lies beneath the epidermis and contains connective tissue, blood vessels, and nerve endings, contributing to the skin's structural integrity and sensory functions. The subcutaneous layer, also known as the hypodermis, consists primarily of fat and connective tissue, serving to insulate the body and allow for flexibility and movement but is not visible from the outside. Therefore, when identifying the layer of skin that is externally visible, the epidermis is the correct choice.