What Really Causes Wrinkles?
Damage occurs to the collagen and elastin fibers in the reticular dermis over time. Expression lines are caused by a "denting" of these fibers from repeated facial movements. Just like a piece of metal that is bent multiple times, the fibers become weaker and weaker and thinner in the area of the constant bend.
If you carefully examine the tissue of sun damaged skin, you will find a disorganized mess in the reticular dermis. Both collagen and elastin fibers are damaged from cumulative sun exposure. Little by little, these fibers are damaged until they cannot function in their intended capacity. This damage results in both skin wrinkling and skin sagging. This is why it is imperative to wear sunscreen!