In aging, two types of fundamental molecular mechanisms in the skin are involved. One of them involves the main cell population of the dermis, fibroblasts, their number and functional activity; the other is associated with a homeostasis disorder of the extracellular matrix (ECM) of the dermis and its main structural component, collagen. With age, the population of dermal fibroblasts is decreasing, primarily due to the depletion of precursor cells, leading to a decrease in the regenerative potential of the skin tissue. At the same time, there are structural, quality, and functional disorders of the dermal ECM associated with its ultrastructural, morphometric, mechanical, and conformational changes, which entail a dysfunction of dermal fibroblasts. The latter contributes to the positive feedback that stimulates further ECM degradation. All these destructive processes form a vicious circle, leading to the constant progression of skin aging. This article describes the cellular and molecular mechanisms of these processes. Their study and understanding are significant since it opens the way for a competent solution and the search for new approaches to solving the extremely urgent skin aging problem.