Question: Why do we get wrinkled or smaller, or have so many problems when we grow old?

Robert Hampson answered on 21 Nov 2014:

Both wrinkles and height loss are caused by the loss of elasticity in different tissues.

Normally young people wake up slightly taller than they were when they went to bed. This is because throughout the night, the cartilage in the back (unburdened by carrying the weight of the body) expands back to its full length. In older people, the cartilage slowly loses this ability and eventually becomes more compressed. Wrinkles are also caused by a loss of elasticity in the skin.

Elasticity is maintained in younger people because their stem cells are constantly making new cartilage and skin cells. More elastic material is always being made. Unfortunately, the more these cells divide the slower it becomes. At some point, there is a specific mechanism which stops them dividing called senescence (old age for cells). This is a specific mechanism evolved to make cancer much less common. However, with no further cell division in the skin, the remaining elasticity slowly fails causing wrinkles. If you constantly damage your skin (by tanning/sun burn for example) then the stem cells have to divide more to repair the skin and aging happens much earlier. Smoking also causes a similar effect in the skin. Sun burn also makes skin cancer more likely due to radiation damage and the necessary over activity of the skins’ stem cells.