What is the term for the outer layer of skin?

The outer layer of skin is referred to as the epidermis. This layer serves several essential functions, including acting as a barrier to protect the underlying tissues from external factors such as pathogens, chemicals, and physical abrasions. The epidermis is composed of stratified squamous epithelium and does not contain blood vessels; instead, it receives nutrients from the underlying dermis.

This layer also plays a critical role in the process of skin renewal, as it constantly sheds dead skin cells and regenerates new ones. Additionally, the epidermis is responsible for the production of melanin, which gives skin its color and provides some protection against ultraviolet radiation.

The other terms refer to different layers or aspects of the skin. The dermis is located beneath the epidermis and contains connective tissue, blood vessels, and nerve endings, while the hypodermis (or subcutaneous layer) lies below the dermis and is composed mainly of fat and connective tissue. The term "stratum" typically refers to specific layers within the epidermis itself, such as the stratum corneum or stratum basale, rather than the entire outer layer of skin.