Keyora Skin Systems Nutrition - Collagen Tripeptides EP-7: The Skin Hydration Response Framework: From Stratum Corneum Water Retention and Barrier Biology to Human Collagen Peptide Evidence

Skin dryness reflects multiple, noninterchangeable physiological properties: stratum corneum water content, intracellular water-binding constituents, epidermal permeability, surface texture, and perceived comfort. Keyora Skin Systems Nutrition - Collagen Tripeptides EP-7 develops the Keyora Skin Hydration Response Framework and its Peptide-to-Hydration Evidence Continuum to connect these distinct endpoints with characterized collagen peptide nutrition and preparation-specific human research. Chapter 1 examines water gradients across epidermal compartments, corneocyte hydration, filaggrin-derived natural moisturizing factors (NMFs), ceramide-cholesterol-fatty acid lipid lamellae, and transepidermal water loss (TEWL). Corneometry measures superficial water-associated properties; TEWL measures outward water-vapor flux. Age, humidity, cleansing, topical care, and test conditions affect interpretation, while subjective tightness and roughness remain separate outcomes. Chapter 2 evaluates the biological context of hydration, including dermal hyaluronan, epidermal NMF constituents, and barrier-associated lipids. Ohara et al. (2010) observed that 200 nmol/mL Pro-Hyp increased hyaluronic acid synthesis 3.8-fold, HAS2 expression 2.3-fold, and proliferation 1.5-fold in cultured human dermal fibroblasts. These cellular responses do not establish a clinical hydration mechanism for orally administered Gly-Pro-Hyp or a finished collagen formula. Chapter 3 reconstructs controlled human trials according to preparation, dose, population, comparator, and endpoint. Asserin et al. (2015) reported significant eight-week facial hydration improvement versus placebo for 10 g/day porcine-derived Peptan P, but not a corresponding significant TEWL effect. Kim et al. (2018) found higher cheek corneometry after 1 g/day sutchi catfish collagen peptides at weeks six and twelve; both trial arms received vitamin C. Miyanaga et al. (2021) investigated 1 and 5 g/day collagen peptides with skin water, NMF, and TEWL assessments. Jung et al. (2021) reported greater hydration, NMF, selected ceramide, and objective roughness responses after 1 g/day AP collagen peptides; the between-group TEWL difference was not significant. Tak et al. (2021) reported significant climate-adjusted, but not unadjusted, TEWL improvement with 1 g/day Nile tilapia skin-derived collagen tripeptides, without significant between-group hydration improvement. Chapter 4 distinguishes measured moisture and texture changes from participant-reported dryness, tightness, and comfort. Chapter 5 applies the framework to Keyora's tilapia-scale hydrolysate, declared as 1,500 mg per two tablets, with 459 Da mean molecular weight and 30% total tripeptides. These specifications neither quantify intact Gly-Pro-Hyp nor demonstrate clinical equivalence to tested preparations. Human studies by Iwai and Yamamoto identified circulating hydroxyproline-containing peptides following distinct collagen hydrolysates, but systemic exposure does not establish the mechanisms underlying clinical NMF or ceramide responses. EP-7 concludes that ingredient identity, circulating peptide exposure, cellular responses, epidermal biochemistry, objective hydration, water loss, and lived skin comfort require separate verification. Integrated scientific interpretation does not replace a randomized trial of the complete Keyora formulation.