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Why do skin cells become flattened and filled with keratin near the surface?

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A pangolin walks through grass with a blue circle around it and the word endangered written in white across the image. — Integument The pangolin is the only mammal in the world covered in scales.

As skin cells, known as keratinocytes, move from the basal layer toward the surface of the epidermis, they undergo a process of maturation and transformation.

The flattening and filling of these cells with keratin are essential steps in forming the stratum corneum, or horny layer. As cells progress through the granular layer, they become laden with keratohyalin, a granular component of keratin. Upon reaching the stratum corneum, the cells lose their nuclei and organelles, becoming progressively flattened and packed with keratin.12

This transformation serves a vital biological purpose: it creates a tough, protective outer barrier that acts as a mechanical defense against infection and prevents the outward loss of water. In this compact zone, the spaces between these flattened, cornified cells are further sealed with lipid (waxy) platelets, which provide an effective barrier against the inward passage of chemicals and the dehydration of the body.314