Which structure acts as a barrier between the exterior environment and the underlying tissues of the skin?

The epidermis serves as the protective outer layer of the skin and acts as the primary barrier between the exterior environment and the underlying tissues. Its main function is to protect the body from environmental threats such as pathogens, chemicals, and physical abrasions.

The epidermis is made up of several layers, the outermost of which is known as the stratum corneum. This layer consists of dead skin cells that are continuously shed and replaced, contributing to the skin's barrier function by preventing water loss and blocking the entry of harmful substances.

While the dermis and collagen are important components of the skin's structure and provide support and elasticity, they do not function as the direct barrier between the environment and the underlying tissues; that role is specifically performed by the epidermis.