Which layer of skin acts as a barrier between the body and the environment?

The epidermis is the outermost layer of the skin and serves as the primary barrier between the body and the external environment. It is composed of stratified squamous epithelial cells, providing essential protection against physical damage, pathogens, and environmental toxins. The epidermis also plays a critical role in preventing water loss, thereby helping maintain hydration within the body.

Additionally, this protective barrier features specialized cells, such as keratinocytes, which produce keratin, a protein that enhances the skin's toughness and waterproofing properties. Melanocytes within the epidermis produce melanin, which provides some protection against ultraviolet radiation from the sun.

In contrast, the dermis lies beneath the epidermis and is responsible for structural support, blood supply, and housing nerve endings, sweat glands, and hair follicles. The subcutaneous layer, also known as the hypodermis, primarily serves as insulation and energy storage. Muscle tissue, which is also listed as an option, does not participate in the barrier function of the skin at all.