Which layer is NOT considered part of the skin?

The hypodermis, also known as the subcutaneous layer, is not considered part of the skin itself. Instead, it serves as a supportive layer located beneath the skin, primarily made up of fat and connective tissues. This layer plays a significant role in insulation, energy storage, and cushioning of the underlying structures, but it does not contribute to the skin's primary functions or structure.

In contrast, the epidermis and dermis are both integral components of the skin. The epidermis is the outermost layer, providing a barrier against environmental factors and pathogens, while the dermis lies beneath it, containing blood vessels, nerves, and supporting elements like collagen and elastin, which contribute to skin strength and flexibility. The stratum corneum, a specific layer within the epidermis, is composed of dead skin cells and provides further protection by forming a barrier to moisture and pathogens.

Understanding the distinction between the hypodermis and the other layers of the skin highlights why it is excluded from the classification of skin structure.