As we age, there is an inevitable deterioration of skin function, loss of structural stability, and gradual loss of skin integrity.
Intrinsic factors are genetically determined, namely the accumulation of harmful products of cellular metabolism and the accelerated aging of cells. Estrogen levels also strongly influence skin integrity, and insufficient estrogen production accelerates aging. Extrinsic factors from the environment can also exacerbate the signs of skin aging.
Understanding the degenerative changes that occur in aging skin at the molecular cellular level will help to provide a deeper understanding of the structural and functional degeneration produced by these changes, thus facilitating the means to treat skin aging and to aid in the regimen to maintain a healthy life.
Endogenous and exogenous causes of skin aging
Intrinsic and extrinsic factors, together, lead to a progressive loss of skin integrity, with both structural stability and physiological function being compromised.
Intrinsic factors of aging are genetically determined to proceed at different rates of aging, which is mainly due to the accumulation of reactive oxygen species (ROS) as a byproduct of cellular metabolism.ROS cause damage to key cellular components such as cell membranes, proteases and genes (DNA). In addition, as individuals age, skin cells age biologically. The proliferation rate of the epidermis begins to decline, leading to continued deterioration of skin structure and function.
Exogenous damage can also contribute to the aging process. For example, ultraviolet light can cause thousands of cellular DNA changes (genetic mutations) every day, causing cumulative damage to the skin and thus accelerating the rate of normal aging. Air pollution or smoking and second-hand smoke environments can also accelerate the natural aging process.
Both the intrinsic and extrinsic effects of skin aging have the potential to contribute to increased skin morbidity. Most people over the age of 65 have at least one skin condition, and many have two or more. The very visible appearance of aging skin is often psychologically distressing. Although rarely fatal, skin disorders can significantly reduce an individual's quality of life in later life. Understanding the basic physiological processes of aging and the extent of their impact on the skin will help the effectiveness of future treatments.
The physiology of aging skin
Cellular senescence: Skin cells have a life cycle and their ability to proliferate and differentiate, as well as their function, gradually declines. Compared to young skin cells, senescent skin cells have a reduced metabolic capacity and "speak the language of the world" at a slower and slower rate of replacement. Many structural and physiological changes occur in aging skin, such as neurosensory, permeability, damage response, repair capacity, and increased incidence of skin diseases.
Keratinocytes change shape as the skin ages, becoming shorter and fatter, while keratinocytes become larger due to decreased epidermal renewal. Melanocytes decrease at a rate of 8-20% per decade, resulting in uneven skin pigmentation in older skin. While the number of sweat glands remains unchanged, sebum production decreases by 60%.
Aging skin has fewer natural water and fat emulsions, less water in the stratum corneum, and up to 65% less overall lipid content. The amount of natural moisturizing factors in the skin is reduced, decreasing its ability to bind water.
A common structural change in aging skin is the flattening of the dermal-epidermal junction by more than one-third (Figure 1), which can be observed by scanning electron microscopy, resulting in reduced resistance to shear forces and greater vulnerability to injury. The smaller continuous surface between the two layers also leads to a reduced supply of cellular nutrients and oxygen, as well as an increased risk of dermal-epidermal separation, a process that may be the mechanism of wrinkle formation.
Although the number of skin cell layers remains stable, the gradual thinning of the skin accelerates in adulthood (see Figure 1), with a decrease in epidermal thickness that becomes more pronounced for women.
Dermal thickness decreases with age, with a reduction in blood vessels and cellular structures, and a decrease in the number of mast cells and fibroblasts. The amount of glycosaminoglycans in the dermis decreases with age, where glycosaminoglycans refer mainly to hyaluronic acid (hyaluronic acid) produced by fibroblasts, and to the extracellular matrix.
Aging is associated with a decrease in collagen synthesis (fibroblast reduction) as well as a decrease in elastin. Elastin also has a higher degree of calcification in aging skin, accompanied by degradation of elastin fibers. Collagen is irreversibly cross-linked, causing collagen bundles to become disorganized.
Loss of dermal layer integrity results in increased rigidity, reduced torsional extensibility, and decreased elasticity. Women's skin may be relatively more prone to ageing (eroding faster in women than in men).
The total amount of subcutaneous fat usually decreases with age and fat distribution changes, for example, fat decreases in the face, hands and feet and increases relatively in the thighs, waist and abdomen.
Skin Anti-aging Tips (for reference only)
Sun protection. Sunlight and ultraviolet rays can be harmful to the skin, so protect yourself from the sun, such as sunscreen and sun protective clothing.
Reduce staying up late. Affect endocrine, injury to the body and face (stay up late smoking) will accelerate the speed of skin aging.
Healthy and balanced diet. Eat more fresh fruits and vegetables to help reduce the damage of skin aging. Avoid sweets. A diet high in sugar or carbohydrates accelerates aging (leading to the accumulation of advanced glycation end products AGEs).
Reduce alcohol consumption. It has been well documented that alcohol is a carcinogen (World Health Organization) and that alcohol produces harmful metabolites in the body, such as aldehydes, that can damage the skin.
Exercise. Life is exercise, and proper exercise improves blood circulation and promotes metabolism.