Photoaging from UV radiation

Photoaging is skin aged before its time by the sun, or more precisely by ultraviolet radiation, UV, absorbed over and over across the years. That radiation doesn't stop at the surface. It reaches the cells and also the extracellular matrix of the dermis, the network of proteins woven underneath the skin that holds it up, like the mesh of threads that gives a fabric its body.

Down there, UV does two things at once. It switches the metalloproteinases into overdrive, enzymes whose job is to break proteins apart, and at the same time it slows the making of collagen, the main protein in that network. More gets broken and less gets replaced, and as the exposures add up the collagen ends up cut into pieces and disordered, like the threads of a fabric that frays and loses its weave.