Which layer of skin is the outermost and does not contain blood vessels?

The epidermis is the correct answer because it is the outermost layer of the skin, serving as a protective barrier for the underlying tissues. This layer is composed primarily of keratinocytes, which are cells that produce keratin, a protein that strengthens the skin and helps deter water loss. Importantly, the epidermis does not contain blood vessels; it is avascular, meaning it relies on the underlying dermis for nutrient exchange and waste removal.

The other layers, such as the dermis, are deeper and do contain blood vessels, supporting the epidermis with nutrients and oxygen. The dermis also houses various structures, including hair follicles and sweat glands. The terms "subcutaneous layer" and "hypodermis" often refer to the same layer beneath the dermis, which is primarily composed of fat and connective tissue, again containing blood vessels. Thus, the unique characteristic of the epidermis being avascular makes it clear why this choice is the most accurate in response to the question.