When we are young we take for granted that skin will pop back in place if pulled on; when we are old we find when our skin is pulled out of place, as between finger and thumb, it does return to its normal position, but slowly. In other words, elasticity has been lost.
There are a number of factors that give the skin its normal elasticity, all related to the components of the intercellular substance, formed and unformed.
The first of these is the volume of intercellular fluid, that is, hydration. It is standard clinical practice when examining a baby that might be dehydrated to pinch the skin and see how rapidly the fold returns to normal. Adults are less likely to lose their skin’s water but severe dehydration will do the same to them, causing a wrinkling of the collapsed skin.
In normal health, and normal hydration, the bundles of collagen, the formed substance of the intercellular tissue, give it a “springy” structure and are a major factor in its elasticity. As we age, the collagen fibers of skin as well as bone become fewer in number and weaker in structure. The skin wrinkles readily, loses its turgor and becomes relatively inelastic.
This problem of collagen fiber insufficiency is exaggerated in the numerous genetically determined collagen malformation conditions such as Ehlers-Danlos syndrome, in which (among many other defects) the normal elasticity of skin is lost and it can be pulled markedly out of shape.
There is another protein structured fiber found in the intercellular substance, and named elastin for its obvious properties. Although this has a part in giving the skin its elastic properties, collagen is probably more important. Another genetically determined congenital defect is named cutis laxa; in this the elastin fibers are not properly formed and the skin hangs in folds.