Photodamage spares the distal digits owing to primate-like hand flexion

Sun-exposed areas of the body - including the face, neck, and extensor forearms - are chronically exposed to UV light and display signs of photoaging. The skin distal to the proximal interphalangeal (PIP) joint is, however, typically spared owing to the natural rest position of the hand. The inward curvature of the fingers, termed the finger flexion cascade, orients the skin distal to the PIP joint toward the ground as in knuckle-walking...