Keratinization Occurs in the Stratum Corneum: Outermost Epidermal Layer

Keratinization (cornification) takes place in the stratum corneum, the outermost layer of the epidermis.

Process

1. Keratinocytes differentiate in stratum basale → spinosum → granulosum.
2. In stratum granulosum: keratohyalin granules, lamellar bodies (lipids).
3. Transition to stratum corneum: nucleus/organelles degrade → keratin filaments aggregate → corneocytes (dead, flattened, keratin-filled).
4. Lipid envelope + corneodesmosomes → barrier.
5. Desquamation: controlled shedding (14–28 day cycle).

Function

Creates the skin's waterproof, mechanical, antimicrobial barrier. Defects → ichthyosis, atopic dermatitis, psoriasis.