Elastin

Elastin is made as soluble tropoelastin, secreted, and deposited onto fibrillin-rich microfibrils, where lysyl oxidase forms the desmosine and isodesmosine crosslinks unique to it. Those crosslinks are distinctive enough to be used to quantify elastin in tissue. The mature protein is extremely hydrophobic and essentially insoluble, and elastic fibres make up only a small percentage of dermal dry weight while accounting for nearly all of the skin's ability to spring back.

The critical number is turnover, which is close to zero. Aspartic acid racemisation puts the human elastin half-life on the order of decades, so the elastic fibre network a person has as a young adult is largely the one they keep. Damage therefore accumulates rather than resolving. Solar elastosis, the build-up of disorganised elastotic material in the papillary and upper reticular dermis, is the defining histological finding of photoageing, driven by ultraviolet induction of elastases.

This makes restoring elasticity a far stronger claim than increasing collagen, because collagen is continuously turned over and elastin is not. A treatment that shifts a cutometer reading has demonstrated a mechanical change, not the deposition of new elastic fibres, and the two should never be equated. It also shifts weight toward prevention: photoprotection preserves a network that cannot be rebuilt.

The characteristic error is selling elastin as a building block. Hydrolysed elastin and tropoelastin in topical products cannot supply the assembly machinery, and elastin-derived fragments such as the VGVAPG hexapeptide act as signalling molecules through the elastin receptor complex, where they are chemotactic and can induce further elastase activity and inflammation. Fragments of a damaged network are a damage signal, not raw material.