keratinointiin

Keratinointi, often termed keratinisaatio in Finnish, is the biological process in which epidermal keratinocytes proliferate in the basal layer, differentiate as they move outward, and eventually form corneocytes rich in keratin. Through this differentiation, a cornified envelope is produced, and the outer epidermal layers become the protective barrier against water loss and pathogens.

During terminal differentiation, cells synthesize keratin filaments and keratohyalin granules; in the stratum granulosum, keratohyalin granules mature to filaggrin, promoting keratin filament aggregation. The cells then cross-link structural proteins such as involucrin and loricrin to form the cornified envelope, while lamellar bodies release lipids that reinforce the lipid barrier.

Keratinization is regulated by signaling pathways including Notch, Wnt, and p63 networks, along with transcription factors such as KLF4 and AP-1. External factors, aging, and nutrition influence the pace of turnover, which in healthy adult skin completes roughly every 28 days.

Disruptions of keratinization underlie several skin disorders. Hyperkeratosis and scaling occur in ichthyosis and psoriasis; impaired barrier function contributes to atopic dermatitis. Abnormal keratinization also affects hair, nails, and wound healing.

Understanding keratinization is central to dermatology and cosmetic science, guiding treatments that normalize differentiation, such as retinoids and moisturizers, and informing the development of keratin-based materials.