What is Skin Aging?
In parallel with the development level of countries, the average life expectancy is increasing thanks to advances in medicine. Aging is a progressive, physiological process characterized by a decrease in biological functions and a deterioration in adaptation to metabolic stress. This process affects the skin as well as other organs. Since it is the organ that reflects the first signs of the natural aging process the earliest, protecting and improving skin quality is gaining importance.

As the life expectancy and the elderly population increase, the desire to look young also increases in parallel and accordingly, rejuvenation (renewal) applications are becoming widespread. In order to select appropriate and reliable methods, the etiopathogenesis of skin aging should be well understood.

As in other organs, morphological and physiological changes occur in the skin with the aging process and loss of function occurs. However, the aging process in the skin is also affected by physical, chemical and mechanical environmental factors. Therefore, skin aging is examined under two main headings:

Intrinsic aging (internal, genetic, chronological aging)

Extrinsic aging (external, photoaging)

Intrinsic (Chronological) Skin Aging
Intrinsic skin aging is a reflection of the general aging of the organism in relation to genetic structure, cellular metabolism and hormonal environment. It affects all layers of the skin and is defined as physiological aging.

Clinically:

The skin is dry, pale, loose, atrophic and thin.

Benign skin tumors may be encountered.

The skin surface is usually smooth and spotless.

Although expression lines become more pronounced, the skin maintains its geometric integrity.

With age, the skin;

Cell renewal

Response to damage

Wound healing

Barrier function

Sensory perception

Thermoregulation

Sweat and sebum production

Many physiological functions such as vitamin D synthesis decrease.

Mechanisms of Intrinsic Skin Aging
There are various theories regarding the pathogenesis of skin aging:

Cellular aging

Decreased DNA repair capacity

Telomere shortening

Mitochondrial DNA mutations

Free radicals and oxidative stress

Chromosome abnormalities and gene mutations

Free Radical Theory
The most widely accepted theory is the free radical theory. According to this theory; cumulative damage caused by continuous exposure of cellular structures (especially DNA) to free radicals causes cell aging or apoptosis.

Molecules such as reactive oxygen species (ROS) O₂⁻, H₂O₂ and OH⁻ increase with external factors such as UV light, environmental pollution, stress, smoking and some drugs. The level of antioxidant enzymes such as superoxide dismutase, catalase and glutathione peroxidase in the skin and antioxidant molecules such as vitamin E, coenzyme Q10 and carotenoids decrease with age. Deficiency of antioxidant systems leads to “oxidative stress”.

ROS activate many receptors on the cell surface; such as EGF, IL-1, TNF-α receptors. This activation can cause apoptosis by stimulating MAP-kinase (p38, JNK) pathways. In addition, transcription factors such as AP-1 and NF-κB activated by these pathways;

Increase MMP (matrix metalloproteinase) production,

Accelerate collagen destruction,

Cause elastic fibers to deteriorate,

Reduce TGF-β and procollagen gene expression.

As a result; dermal matrix is ​​deteriorated, elasticity decreases and wrinkles become more pronounced.

Telomere Shortening
Telomers are repetitive DNA sequences located at the ends of chromosomes. Telomeres shorten with each cell division. When a critical length is reached, cell division stops and the cell enters senescence. Telomerase enzyme is active in some stem cells and basal keratinocytes, but not in fibroblasts. Therefore, the protective effect of telomerase in skin aging is limited.

Genetic Factors
The role of some single gene mutations has been shown in premature aging syndromes. However, a specific gene that directly determines aging has not yet been identified. It is thought that aging is mostly due to a decrease in DNA synthesis and disorders in repair mechanisms.

Retinoic Acid Receptors
Retinoic acid receptor alpha (RAR-α) expression increases in intrinsic aging. It is known that this increase causes an increase in the MMP-1 enzyme. No significant change has been observed in other retinoid receptors.

The Role of Hormones
Estrogen; It has an effect on the skin, hair, connective tissue and immune system. In women, estrogen levels decrease by approximately 90% after menopause. During this period;

Collagen in the skin decreases,

Water retention capacity decreases,

Elasticity deteriorates,

Wrinkles increase.

Skin aging has been observed to be less pronounced in women receiving hormone replacement therapy.