Introduction
The ultraviolet radiation from the sun has damaging effects on human skin. Excessive exposure to the ultraviolet rays from sunlight will cause premature aging, damage the human body's cells and tissue, and effects deoxyribonucleic acids (DNAs). The premature aging of the cells by sun exposure is called photoaging. It primarily depends upon the amount of melanin in the skin and the degree of exposure to ultraviolet rays. It activates the receptors on the surface of keratinocytes and fibroblasts (cells in the skin), leading to collagen breakdown and preventing new collagen synthesis. The collagen breakdown, followed by inefficient collagen synthesis, will lead to a defect in the integrity of the skin resulting in clinically visible wrinkles and skin atrophy.
Several studies have confirmed that the process involved in cellular damage during ultraviolet ray exposure is the oxidation of cellular biomolecules. The oxidation of cells can be prevented by prior skin treatment with antioxidants and by preventing the depletion of natural antioxidants in the skin. The antioxidative property of skin depends upon the vitamins and nutritional factors, and the antioxidative effects are produced when these work concurrently.
What Are the Clinical Signs of Photoaging?
The chronological aging of an individual is predetermined and depends on one's physiological predisposition. However, photoaging is something different. People with a history of excessive sun exposure, living in tropical areas, and skin with less melanin are frequently at risk of developing ultraviolet rays-induced photodamage to the cells and tissue. Clinical signs of photoaging are seen on the most sun-exposed areas of the skin and include
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Wrinkles.
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Mottled pigmentation (hyper or hypopigmentation).
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Uneven skin tone and dullness.
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Rough skin.
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Dehydrated appearance.
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Severe atrophy of the skin.
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Telangiectasias (spider-like veins visible underneath the skin).
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Solar elastosis.
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Leathery appearance.
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Laxity (a loose limb or muscle).
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Skin cancer and melanoma.
However, chronological aging is associated with fine wrinkles and laxity and does not show hyperpigmentation or deep wrinkles as in photoaging. Exposure to UV-B rays greatly increased angiogenesis and skin vascularisation.
What Are the Causes of Photoaging?
The ultraviolet (UV rays) from sunlight are the main contributor to photoaging in human beings. The exposure of humans to natural and artificial ultraviolet rays has increased drastically over the past 50 years. One main reason for the increased exposure to natural UV rays is ozone layer depletion. Ultraviolet rays are of 3 types.
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UV-A:
The UV-A rays were thought to be least damaging to the skin earlier. However, studies reveal that UV-A rays can penetrate the deep skin layers and exhibit severe damage. They have a wavelength of 320 to 400 nanometers and are found abundantly in sunlight. Though the UV-A rays have less penetrative power, the higher concentration in sunlight contributes to the higher amount of damage caused by UV-A rays.
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UV-B:
The UV-B rays have a wavelength between 290 to 320 nanometers and affect the superficial layer of skin. It is associated with sunburns following sun exposure. It cannot penetrate through glass.
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UV-C:
UV-C radiation falls in the low wavelength group between 100 to 290 nanometers. It is absorbed by the ozone layer and does not affect the skin.
What Are the Effects of Ultra Violet Rays on the Cells and Tissues?
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Ultraviolet rays have carcinogenic effects on human cells and tissues, with the maximum effect shown by UV-B and fewer effects by UV-A and UV-C. UV-A rays cause deoxyribonucleic acid (DNA) damage by producing short-lived reactive oxygen species through endogenous photosensitizers. It includes superoxides, singlet oxygen, and hydrogen peroxide. It also causes bond breakage in the cell DNAs. In addition, people with less melanin pigment in the skin (fair people) had higher chances of developing photodamage and were more prone to skin carcinomas.
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The ultraviolet rays will activate complex biochemical events in human skin. Its molecular changes and the breakdown of collagen lead to skin integrity loss. The reactive oxygen species produced by the UV-A will produce matrix metalloproteinases that will contribute to the further degradation of collagen and the connective tissue components of the skin. It also inhibits the production of collagen, hindering the reparative process too.
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Collagen destruction is considered the hallmark of photoaging. Irradiating the keratinocytes with UV-B produces matrix metalloproteinases and is responsible for connective tissue changes; they are involved in the destruction and remodeling of the extracellular matrix.
What Are the Endogenous Antioxidants That Protect the Skin Against Photoaging?
Several antioxidants are present in the dermis and epidermis of the skin that protects the skin from harmful ultraviolet rays and prevents photoaging and photodamaging. Some endogenous antioxidants are glutathione (GSH), ascorbate, superoxide dismutase (SOD), ubiquinol, and catalase. In healthy skin, the attack by reactive oxygen species will trigger a series of events that will develop a complex defense mechanism by the antioxidants. However, continuous sun exposure will deplete the endogenous antioxidants in different layers of the skin, making the skin more prone to photoaging.
What Are the Exogenous Antioxidants?
Exogenous antioxidants are those synthesized from external sources like fruits or plants. The exogenous antioxidants have photoprotective and damage-reversal effects. Some of the exogenous antioxidants are given below.
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Ascorbic Acid:
Topical vitamin C will reverse the photodamage by stimulating collagen production and also acts as a photo protectant.
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Vitamin E:
It stabilizes the skin barrier and compliments the other antioxidants.
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Lycopene:
Protects the skin from UV-induced erythema (redness).
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Carotenoids:
Actively photoprotect the cells and destroy the reactive oxygen species. It also decreases the erythema caused by sun exposure.
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Tretinoin:
Diminishes the signs of photoaging and increases collagen synthesis.
Conclusion
Protecting the skin from excessive sun exposure is one major measure that people can take to prevent photoaging to some extent. Studies have revealed that oral intake of specific micronutrients and phytochemicals will protect the skin from the photoaging effects of ultraviolet ray exposure. However, a good photoprotective action could be reached only if an optimal level of antioxidants has reached the skin. Several studies and research has continuously demonstrated the photoprotective activities of various pharmaceuticals.
