Skin irradiation with ultraviolet rays

Ultraviolet irradiation is the therapeutic use of UV radiation.

Like many physiotherapeutic methods used in cosmetology, UV irradiation was initially used for therapeutic purposes (including the treatment of acne, alopecia, vitiligo, etc.) and only after some time began to be used for aesthetic purposes (as an alternative to natural tanning).

Ultraviolet (UV) radiation was discovered in 1801 by I. Ritter, W. Herschel and W. Wollaston. In the first half of the 20th century, it accounted for just over 1% of the optical spectrum reaching the earth's surface. However, over the past 50 years, due to unfavorable environmental conditions and thinning of the stratospheric ozone layer, this figure has increased to 3-5%.

UV rays are absorbed by various layers of the skin and penetrate into tissues to an insignificant depth - 0.1-1.0 mm. The absorption processes and permeability of UV rays depend on such properties of the skin as the thickness of the epidermis, its pigmentation, the degree of hydration and blood supply, the content of carotenoids and uric acid. The wavelength is of some importance. UV rays mainly of the "C" region (UV) with a wavelength of less than 280 nm are absorbed by the stratum corneum of the epidermis.

UV rays "B" (280-320 nm) penetrate 85-90% of all layers of the epidermis, and 10-15% of these rays reach the papillary layer of the dermis. At the same time, UV rays with a wavelength of more than 320 nm, i.e. the "A" region, are absorbed and penetrate into the deeper layers of the dermis, reaching its reticular layer. In white people, UV rays penetrate deeper, in black people they are absorbed by the superficial layers of the skin due to the presence of a large amount of melanin pigment in it.

UV radiation is a necessary factor for the normal functioning of the human body. Of course, it has the most pronounced direct effect on the skin. However, due to complex neuro-reflex and neurohumoral reactions, UV radiation significantly affects the condition of many internal organs, metabolic processes, hematopoiesis, and adaptive reactions, which is the basis for its therapeutic and prophylactic use.

In recent years, many experts have been talking about the adverse effects of UV radiation, including artificial sources, on the human body, especially on the skin.

Longwave radiation

Long-wave ultraviolet rays (LWUV rays) stimulate the transport of melanin granules from the soma of melanocytes located among the cells of the basal layer of the epidermis along numerous processes diverging in different directions, which causes pigmentation (fast tanning) of the skin. Melanin appears after 2 hours, but does not protect the skin from sunburn. Melanin is a powerful antioxidant and suppresses the activation of lipid peroxidation by toxic oxygen metabolites. Irradiation with a wavelength of 340-360 nm has the maximum melanin-transporting effect.

The products of photodestruction covalently bind to skin proteins and form antigenic peptides that come into contact with Langerhans cells of the suprabasal layer of the epidermis. These cells, which have antigen-presenting properties, move to the dermis and initiate the formation of a cellular immune response. The processes described above are initiated after 15-16 hours and reach a maximum after 24-48 hours after the initiation of the antigenic peptide. Depending on the state of the organism and the duration of irradiation, the composition of the cellular population of the immune response can change significantly. Repeated contact with photodestructive antigenic peptides increases the number of the clone of T-lymphocytes that recognize them. Consequently, regular UF-irradiation, in addition to expanding the antigen-recognizing "repertoire" of T-lymphocytes, increases the level of the organism's immunoresistance to the effects of unfavorable environmental factors. At the same time, prolonged DUV irradiation leads to almost complete disappearance of Langerhans cells from the epidermis and weakening of the presentation of photodestruction products by patrolling T-lymphocytes of the epidermis. Having penetrated the dermis, DUV-induced antigen peptides activate antigen-specific T-suppressors, which block the initiation of T-helpers, which can cause blast transformation of skin cellular elements.

Therapeutic effects: melanin-transporting, immunostimulating.

Medium wave radiation

Different doses of ultraviolet radiation determine the unequal probability of formation and manifestation of therapeutic effects. Based on this, the effect of medium-wave ultraviolet radiation in suberythemal and erythemal doses is considered separately.

In the first case, UV radiation in the range of 305-320 nm stimulates the decarboxylation of tyrosine with subsequent formation of melanin in melanocytes. Increased melanogenesis leads to compensatory activation of the synthesis of adrenocorticotropic and melanin-stimulating hormones of the pituitary gland, which regulate the secretory activity of the adrenal glands.

When irradiated with medium-wave ultraviolet rays (280-310 nm) of the lipids of the surface layers of the skin, the synthesis of vitamin D is triggered, which regulates the excretion of calcium and phosphate ions in the urine and the accumulation of calcium in bone tissue.

With increasing intensity of UV radiation (erythemal doses), photodestruction products - antigenic peptides - are transported by Langerhans cells from the epidermis to the dermis by sequential recruitment and proliferation of T-lymphocytes, causing the formation of immunoglobulins A, M and E, and granulation of mast cells (basophils and eosinophils) with the release of histamine, heparin, platelet activating factor (PAF) and other compounds that regulate the tone and permeability of skin vessels. As a result, biologically active substances (plasmakinins, prostaglandins, arachidonic acid derivatives, heparin) and vasoactive mediators (acetylcholine and histamine) are released in the adjacent layers of the skin and vessels. Through molecular receptors they activate ligand-gated ion channels of neutrophils and lymphocytes and, by activating endothelial hormones (endothelins, nitric oxide, nitric superoxide, hydrogen peroxide), significantly increase vascular tone and local blood flow. This leads to the formation of limited hyperemia of the skin - erythema. It occurs 3-12 hours after irradiation, lasts up to 3 seconds, has clear boundaries and an even red-violet color. Further development of the reaction is interrupted due to an increase in the content of cis-urocanic acid in the dermis, which has a pronounced immunosuppressive effect. Its concentration reaches a maximum in 1-3 hours and returns to normal 3 weeks after irradiation. Erythema leads to dehydration and a decrease in edema, a decrease in alteration, suppression of the infiltrative-exudative phase of inflammation in the tissues and internal organs segmentally associated with the irradiation area.

The reflex reactions that occur during UV irradiation stimulate the activity of almost all body systems. The adaptive-trophic function of the sympathetic nervous system is activated and the impaired processes of protein, carbohydrate and lipid metabolism in the body are restored. The sensitivity of the skin of a healthy person to UV radiation depends on the time of previous irradiation and, to a lesser extent, on hereditary pigmentation. In the spring, sensitivity increases and decreases in the fall. The skin of different areas of the human body has different sensitivity to ultraviolet radiation. Maximum sensitivity is recorded in the upper back and lower abdomen, and minimum - on the skin of the hands and feet.

Therapeutic effects: melanin-synthesizing, vitamin-forming, trophostimulating, immunomodulatory (suberythemal doses), anti-inflammatory, desensitizing (erythemal doses).

Shortwave radiation

Shortwave irradiation is the therapeutic use of shortwave ultraviolet radiation. It causes denaturation and photolysis of nucleic acids and proteins. The resulting lethal mutations with ionization of atoms and molecules lead to inactivation and destruction of the structure of microorganisms and fungi.

Therapeutic effects: bactericidal and mycocidal.

When schematically representing the histological and biochemical reactions that occur in the epidermis and the skin itself under the influence of UV radiation, we can talk about the following changes. The skin contains many so-called chromophores - molecules that absorb significant amounts of UV radiation with certain wavelengths. These include, first of all, protein compounds and nucleic acids, trans-isomer of urocanic acid (absorption of UV radiation in the spectrum of 240-300 nm), deaminated histidine, melanin (350-1200 nm), aromatic amino acids of protein molecules in the form of tryptophan and tyrosine (285-280 nm), nitrogen compounds of nucleic acids (250-270 nm), porphyrin compounds (400-320 nm), etc. Under the influence of absorption of UV radiation in the chromophore substances of the epidermis and dermis, the most pronounced photochemical reactions occur, the energy of which leads to the formation of active forms of oxygen, hydrogen peroxide radicals and other free radical compounds. In turn, these substances react with DNA molecules and other protein structures, which can lead to undesirable consequences and changes in the genetic apparatus of the cell.

Thus, with maximum absorption of UV radiation, proteins and nucleic acids are primarily affected. However, as a result of free radical reactions, the lipid structures of the epidermis and cell membranes are damaged. UV radiation increases the activity of metalloproteinases, which can cause degenerative changes in the intercellular substance of the dermis.

As a rule, adverse effects most often arise from the action of UV radiation of the "C" (280-180 nm) and "B" (320-280 nm) regions, causing the strongest reactions in the epidermis. UHF radiation (region "A" - 400-320 nm) has a softer effect, mainly on the dermis. Histological studies devoted to adverse changes in skin cells under the influence of UV irradiation in the form of dyskeratosis, mast cell degranulation, reduction of Langerhans cells, inhibition of DNA and RNA synthesis, are described in great detail by dermatologists and cosmetologists studying photoaging of the skin.

The above changes in the morphological condition of the skin usually occur with excessive, inadequate irradiation in the sun, in solariums, and with the use of artificial sources. Degenerative changes in the epidermis and in the skin itself are manifested by an increase in the mitotic activity of the germ layer of the epidermis, an acceleration of keratinization processes. This is expressed in thickening of the epidermis, the appearance of a large number of completely keratinized cells. The skin becomes dense, dry, easily wrinkles and ages prematurely. At the same time, this skin condition is temporary.

Of course, there is a positive effect of UV rays on the body. Under their influence, vitamin D is synthesized, which is so necessary for the body to absorb calcium and phosphorus, and to form and restore bone tissue. In some skin diseases, UV irradiation has a therapeutic effect and is called heliotherapy. But in this case, it is necessary to follow the doctor's recommendations. Skin reaction to UV irradiation:

• thickening of the stratum corneum and reflection or absorption of light by keratin;
• production of melanin, the pigment granules of which dissipate the absorbed solar energy;
• the formation and accumulation of urocanic acid, which, by changing from the cis-form to the trans-form, promotes the neutralization of energy;
• selective accumulation of carotenoids in the dermis and hypodermis, where beta-carotene acts as a stabilizer of cell membranes and an absorber of oxygen radicals formed when porphyrins are damaged by UV rays;
• production of superoxide dismutase, glutathione peroxidase and other enzymes that neutralize oxygen radicals;
• restoration of damaged DNA and normalization of the replication process.

In case of disruption of the protective mechanisms, depending on the intensity, wavelength and penetrating power of the sun's rays, tissue damage of varying degrees is possible - from mild erythema, sunburn to the formation of skin neoplasms.

Negative factors of UV radiation:

• burn;
• eye damage;
• photo aging;
• the risk of developing cancer.

Recommendations for receiving UV radiation:

• Before tanning, you need to prepare the skin of your face and body: remove makeup, take a shower, use a scrub or gommage.
• Avoid applying perfumes, cosmetics (except professional products for stimulating melanogenesis, protection and moisturizing)
• Take into account the intake of medications (antibiotics, sulfonamides and others that increase the sensitivity of the skin to UV radiation).
• Use special glasses to protect your eyes and cream to protect the red border of your lips.
• It is recommended to protect hair from direct exposure to UV rays.
• It is recommended to avoid direct exposure of the nipple area of the mammary gland and genitals to UV rays.
• After UV exposure, it is recommended to take a shower and apply a special moisturizing cream. Using a scrub after insolation is not justified.
• If the patient has any dermatological diseases, it is necessary to consult a dermatologist.

The distance from the patient's body to the source of integral UV radiation is 75-100 cm; DUV + SUV radiation - 50-75 cm; DUV radiation - at least 15-20 cm.

The dosage of procedures is carried out using different methods: by biodose, by intensity (density) of energy in J/m2 ^or by the duration of irradiation specified in the instructions for the irradiator and selected taking into account the sensitivity of the skin to UV radiation.

During the period of irradiation, especially in the winter-spring season, it is recommended to take multivitamins, especially vitamin C. Continuous UV irradiation throughout the year is not indicated.

Between courses of irradiation in solariums or photoriums, it is necessary to make intervals to restore the optical properties of the skin and normalize the activity of the body. Control the disinfection of sunbeds, floor coverings, protective glasses.