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There are two ways in which skin aging occurs: genetically coded intrinsic mechanisms and extrinsic processes related to external factors.
Shortening of telomeres (the DNA sequence at the end of each chromosome) during cell division plays a role in natural (intrinsic) aging: it maximizes the number of cell divisions. The genes involved in the regulation of apoptosis (aging on the cellular level) also play a major role.
The other theory emphasizes the role of by-products, highly reactive molecules (free radicals) released during metabolic processes, as these agents interfere with cellular functions by altering DNA, membrane components, receptors and the components of signal transduction pathways and they are responsible for aging.
Aging skin is characterized by a gradual decrease in skin functions, atrophy, increased wrinkling, reduced elasticity, reduced pigment content, hair loss, graying, slow wound healing, reduced excretion of foreign substances, reduction of subcutaneous fat tissue. All these features result in dry, dull, vulnerable skin, with skin tumors becoming more common (fibromas, keratosis).
Environmental factors are also involved in extrinsic aging, especially UV radiation from sunlight, smoking, increased sympathetic tone (stress), and illnesses. UVB rays fall into the absorption spectrum of DNA, thus promoting the damage of the hereditary material and the formation of skin cancer. Longer wavelength UVA rays damage cellular components (membranes, receptor proteins, DNA) through the formation of reactive oxygen radicals. The signs of skin aging therefore appear sooner on the exposed skin areas (face, hand, neckline).
UV reduces collagen production, hyaluronic acid production and promotes degradation; extracellular matrix degrades and its composition changes, e.g. large amounts of abnormal elastin (elastic fiber) accumulate while the amount of normal elastin decreases (solar elastosis). Cumulative sunlight exposure results in pigmented lesions (lentigo solaris).
As a result of the combination of the above factors, half as much hyaluronic acid is produced in the skin by the age of 40 as in our younger years. By the age of 60, the hyaluronic acid content of the skin is only 10% of the original.