The epidermis is in a constant state of renewal, a process driven by keratinocytes, specialized cells that proliferate, differentiate, and migrate to the skin surface. These cells are responsible for producing keratin, a fibrous structural protein that makes up approximately 90% of the skin’s composition. Keratin is synthesized from essential amino acids, with cysteine playing a pivotal role due to its sulfur-containing side chain. This unique feature enables the formation of disulfide bridges, which reinforce the mechanical strength and resilience of the skin barrier. The dynamic activity of keratinocytes and the biochemical properties of keratin are central to maintaining epidermal integrity, protection, and overall skin health.