Chronological Aging and Wrinkles
As a person ages the epidermal cells become thinner and less sticky. The thinner cells make the skin look noticeably thinner. The decreased stickiness of the cells decreases the effectiveness of the barrier function allowing moisture to be released instead of being kept in the skin. This causes dryness. The number of epidermal cells decreases by 10% per decade and they divide more slowly as we age making the skin less able to repair itself quickly.
The effects of aging on the dermal layer are significant. Not only does the dermal layer thin, but also less collagen is produced, and the elastin fibers that provide elasticity wear out. These changes in the scaffolding of the skin cause the skin to wrinkle and sag. Also, sebaceous glands get bigger but produce less sebum, and the number of sweat glands decreases. Both of these changes lead to skin dryness. The rete-ridges of the dermal-epidermal junction flatten out, making the skin more fragile and making it easier for the skin to shear. This process also decreases the amount of nutrients available to the epidermis by decreasing the surface area in contact with the dermis, also interfering with the skin’s normal repair process.
In the subcutaneous layer the fat cells get smaller with age. This leads to more noticeable wrinkles and sagging, as the fat cells cannot “fill in” the damage from the other layers. Exposure to ultraviolet light, UVA or UVB, from sunlight accounts for 90% of the symptoms of premature skin aging. Most of the photoaging effects occur by age 20. The amount of damage to the skin caused by the sun is determined by the total lifetime amount of radiation exposure and the person’s pigment protection.