What is the formal name for the horny layer of the skin?

The formal name for the horny layer of the skin is the stratum corneum. This outermost layer of the epidermis consists of many dead, flattened keratinocytes that have lost their nuclei and cytoplasmic organelles, making it a protective barrier for the underlying layers. The primary function of the stratum corneum is to prevent water loss and protect the underlying tissues from environmental factors such as pathogens, toxins, and physical abrasions.

In contrast, the other layers mentioned serve different roles within the skin. The stratum lucidum is a thin, clear layer found only in certain areas of the skin (like the palms of the hands and soles of the feet) and provides an extra layer of protection. The stratum granulosum contains living cells that begin the process of keratinization, where they transform into the more flattened, dead cells found in the stratum corneum. Lastly, the stratum basale is the deepest layer of the epidermis that is responsible for the generation of new skin cells. Each of these layers contributes to skin health and function, but the stratum corneum specifically denotes the outermost protective layer, making it the correct answer in this context.