PSI Barbering Practice Exam 2025 – All-in-One Resource to Master Your Certification!

The outermost layer of the epidermis, known as the stratum corneum, is indeed covered by a thin layer of sebum, which is an oily substance produced by sebaceous glands. This layer of sebum serves several key functions, one of which is to create a waterproof barrier on the skin. This barrier helps to prevent water loss from the body and protects the underlying layers of the skin from external elements, such as bacteria, pollutants, and environmental damage.

While hydration is essential for skin health, the presence of sebum specifically contributes to its waterproof properties, rather than hydration directly. Although skin can appear colorful or reflective depending on factors like health, skin type, and the presence of cosmetics, these qualities are not inherently linked to sebum. Therefore, the primary function of the sebum layer is to keep the skin waterproof, making it the most relevant answer to the question.