Final answer:
Wrinkles or sagging skin occur due to decreased collagen and elastin production, weakening of muscles, and decreased skin hydration.
Step-by-step explanation:
Wrinkles or sagging skin occur due to breakdown of the skin's structure, which results from decreased collagen and elastin production in the dermis, weakening of the muscles lying under the skin, and the inability of the skin to retain adequate moisture.
Increased collagen production (option a) and elasticity of the skin (option b) are actually factors that help prevent wrinkles and sagging skin. Regular exercise (option d) can also contribute to healthy skin, but it is not directly related to the cause of wrinkles or sagging skin.
On the other hand, decreased skin hydration (option c) is a cause of wrinkles or sagging skin. As the skin becomes dehydrated, it loses its plumpness and elasticity, leading to the formation of wrinkles and sagging.