Which layer of skin should not be penetrated during aesthetic treatments?

The stratum corneum is the outermost layer of the skin and acts as a protective barrier against environmental hazards, pathogens, and loss of moisture. During aesthetic treatments, it is essential to avoid penetrating this layer because it serves a crucial function in maintaining the skin's overall health and integrity. Disturbing the stratum corneum can lead to skin irritation, increased sensitivity, and even compromise the skin’s barrier function, leading to further issues such as dryness and infection.

Each of the other layers listed, such as the stratum granulosum, stratum lucidum, and stratum basale, are deeper within the skin and typically are not targeted during most aesthetic treatments to protect the skin's surface integrity and avoid potential complications. The focus on the stratum corneum ensures that treatments are effective while minimizing adverse effects on the skin.