A collagen fragment sold in leave-on creams at a few parts per million. Human evidence is modest and narrow: fewer fine lines on the treated side of a face. Firmness and hydration improve inconsistently. Little to fear — nothing measurable enters the bloodstream. Vitamin A creams have a far larger evidence base for the same goal. (Full Review)
| Marker | Target | Why |
|---|---|---|
| Wrinkle severity grade (photonumeric scale 0–4) | No established target value; at least a 1-grade improvement against the individual's own baseline photograph | The primary appearance endpoint the trials used |
| Corneometry (skin hydration) | Above 45 arbitrary units on the cheek | Hydration drives perceived smoothness and confounds wrinkle scoring |
| Transepidermal water loss (TEWL) | Below 12 g/m²/h on the face | A rising value is the earliest sign of irritation from the product or its excipients |
| Cutometry R2 (gross elasticity) | Above 0.80 on the 0–1 ratio | Elasticity is the endpoint where the peptide evidence is most conflicted |
| Plasma vitamin C | 50–70 µmol/L | Required cofactor for the enzymes that hydroxylate collagen; a deficient dermis cannot act on the signal |
| Glycated hemoglobin (HbA1c) | 4.8–5.2% | High blood sugar cross-links dermal collagen and stiffens it, capping any achievable gain |
| 25-hydroxyvitamin D | 40–60 ng/mL | Supports keratinocyte turnover and barrier repair, both of which gate topical response |
Cadence: Photographs and instrument readings at 4 weeks, at 12 weeks, then every 6 months for as long as use continues; blood markers annually, or sooner if a baseline value fell outside the functional range.