What passes through the stratum lucidum?

The stratum lucidum is a thin, clear layer of epidermis found largely in the thick skin of the palms and soles. Its main function is to provide an additional layer of protection and to contribute to the overall structural integrity of the skin.

Light is able to pass through the stratum lucidum due to its translucent nature. This layer contains keratinocytes that are densely packed with eleidin, a clear protein that eventually transforms into keratin. This unique composition allows for the passage of light rather than blocking it, which is crucial in the context of skin health and function.

On the other hand, the other options—oxygen, water, and heat—do not accurately describe what can pass through this particular layer. Oxygen and water typically do not pass directly through the stratum lucidum; instead, they are exchanged through underlying skin layers, while heat is regulated by the vascular system and does not "pass through" the skin layers in the same manner as light does.