Washington Esthetician State Board Practice Exam

What passes through the stratum lucidum?

1. Water

2. Light

3. Oxygen

4. Cells

The correct answer is: Light

The stratum lucidum is a thin, clear layer of skin found only in certain areas of the body, particularly in the palms of the hands and the soles of the feet. It functions primarily as a protective barrier and is made up of dead keratinocytes that provide an extra layer of toughness. Among the provided options, light is the correct answer as it can pass through the stratum lucidum. This layer is translucent, allowing light to penetrate but not allowing significant amounts of other substances, such as water or oxygen, to pass through it effectively. Water typically cannot pass through this layer easily, as the skin's outer layers are designed to minimize water loss. Oxygen is not transported through the epidermis, including the stratum lucidum, as it relies on blood vessels in the dermis for oxygen supply. Similarly, cells do not pass through this layer because it consists of dead cells; new cells are produced deeper in the epidermis and move up through the layers as they mature. Thus, the unique structure and composition of the stratum lucidum enables light to pass through while blocking many other substances.