Oregon Esthetician State Board

What is the fourth layer of the epidermis?

1. Stratum corneum

2. Stratum lucidum

3. Stratum spinosum

4. Stratum granulosum

The correct answer is: Stratum spinosum

The fourth layer of the epidermis is the stratum granulosum. This layer is significant as it plays a pivotal role in the transition of cells from living to dead keratinized cells, which are crucial for the protective function of the skin. The stratum granulosum contains keratinocytes that begin to die and dehydrate, losing their nuclei as they move upward in the epidermis. During this process, they produce keratohyalin granules, which contribute to the formation of keratin, an essential protein for skin structure and barrier function. The recognition of the stratum granulosum as the fourth layer reflects its position between the more active and living lower layers of the epidermis and the outermost layer, the stratum corneum, which consists of fully keratinized, dead cells. Understanding this layer and its functions is essential for estheticians as it helps inform treatments aimed at enhancing skin health and appearance.