Laser treatment and skin barrier

Skin is the body’s largest organ covering the entire body surface and playing an important role as a barrier. The stratum corneum of the skin located at the outermost layer of the epidermis was once thought to be a structure formed by useless dead cells. However, recent studies have found that keratinocytes and their extracellular components are closely linked to each other, providing a barrier for penetration. The skin barrier is often compared to the “brick wall” structure. The keratinocytes are like the “bricks” of the wall, while the lipids between the cells are like the “mortar” of the wall. It connects the keratinocytes tightly, making the skin barrier normal, ensuring neither losing moisture nor being invaded by the outside world.Besides, there is a layer of hydro-lipid film, which, together with the brick structure, constitutes the physical barrier of skin. One of the most popular and widely used fields in laser medicine is the laser treatment of skin diseases. In the treatment process, laser often damages the normal structure of the skin and affects the physiological function of the skin, thus affecting the effect of laser treatment. In this essay we focus on the effect of different forms of laser action on skin barrier function and repair.

1. Effects of laser treatment on the skin barrier

Laser has the advantage that light comes from common source cannot compare. So it has special application in domain of dermatology consequently. When biological tissue absorbs laser energy, a series of energy conversion processes may occur: light energy turns to heat energy, chemical energy, mechanical energy or the internal energy of living matter. These physical and chemical processes are called laser tissue effect. At the same time, the further action of these physical and chemical factors on biological tissues may lead to morphological and functional changes of life substances at the molecular, cellular and tissue levels.According to the energy conversion mode of laser, the interaction between laser and skin can be divided into three types: photochemical effect, photothermal effect and photomechanical effect.

1.1 Photochemical effect of laser treatment

The photochemical effect, also known as the nonthermal effect, is the energy of a laser photon that can excite specific biological molecules and induce a chemical reaction. Photosynthetic of green plants, animal vision, photoinduced denaturation of coatings and macromolecular materials, photolithography, photocatalysis are all related to organic chemical reactions. The mechanism of action is mainly shown in five aspects: photoisomerization, photosynthesis, photodissociation and photosensitization, as well as biological stimulation of laser. The most widely used photochemical effect in medicine is photosensitization, of which photodynamic therapy (PTD) is the most representative.

The mechanism of action of PDT is that the photosensitizer in the tissue under aerobic conditions is stimulated by laser. Through a series of photochemical reactions, a large number of reactive oxygen substances are produced, thus damaging the target tissue to achieve the purpose of treatment. PDT with precise targeting characteristics has been widely used in various fields of medical treatment, mainly for solid tumors and vascular diseases. The former such as skin tumors, nasopharyngeal cancer, laryngeal cancer, brain glioma, lung cancer, bladder cancer, breast cancer, and gastrointestinal tumors.The latter such as macular degeneration, esophageal varices, such as bright red mole. PDT also has some anti-microbial effects, which can improve periodontal disease by controlling plaque and treat HPV infections such as condyloma acuminatum. In addition, PDT can also treat a variety of skin diseases such as acne, photoaging, psoriasis, and porocortex keratosis. PDT can down-regulate the expressions of toll-like receptor 2 and toll-like receptor 4 in epidermis and sebaceous glands. The decrease of intercellular lipid synthesis in the cutin layer of skin will occur in the short term after light irradiation, resulting in the decreased ability of intercellular adhesion of the cutin layer of skin, resulting in the destruction of the skin brick wall structure, temporarily reducing the skin’s moisturizing function, and the appearance of erythema, dryness and dandruff in the short term. After treated by PDT, patients’ skin becomes thin. Dermal collagen in shallow, Ⅰand Ⅲ type former collagen increased. And which can stimulate collagen hyperplasia of TGF – beta and Ⅱ TGF – beta receptors expression significantly higher, while MMP1, MMP3 and MMP12 expression is reduced. So it can improve the texture of skin, appearance treatment of photoaging. Ji studied the photoaging patients and found that PDT can improve the skin appearance and skin moisture content. Therefore, PDT has no direct damage to skin barrier function, and in the long term, it can increase skin moisture content and improve skin barrier function. Therefore, postoperative moisturizing repair is adopted after treatment to avoid adverse reactions of skin barrier damage.

1.2 Photothermal effect of laser treatment

The process of converting light energy into biological tissue heat energy after the biological tissue absorbs laser energy is called photothermal effect. Since temperature determines the state of motion of molecules, the biological effects of laser on tissue are determined by the temperature reached. For skin, when the temperature rises to 38 ~ 40 ℃, it has warm feeling. When the temperature rose to 43 ~ 44 ℃, the temperature expand vascular engorgement, occurrence erythema of floor of a few seconds then, after a few minutes can appear a small amount of inflammatory exudate, and mild edema, but does not cause irreversible damage. Skin temperature rises to 47 ~ 48 ℃, few seconds there is inflammatory exudate retention in the skin, causing the epidermis and the dermis separation form blisters. When the temperature rise to 60 ~ 100 ℃, about 10 seconds can lead to the skin, skin thin cell coagulation necrosis. When the temperature exceeds 100 ℃, the skin tissue is boiling evaporation, the steam pressure caused by the rapid increase and damage cells and blood vessels. If the temperature continues to increase, the skin begins to dehydrate and carbonise. The laser treatment of skin diseases is mainly based on the photothermal effect of laser.According to different principles, it can be divided into two categories: stripping and non-stripping.

1.2.1 Exfoliative laser treatment

Exfoliative laser can remove the damaged or aged epidermis and part of the dermal tissue, and induce epidermis and dermal regeneration and remodeling, so as to remove freckles, wrinkles and tender skin. Exfoliative laser treatment is suitable for grinding, perforating or resection of various vegetations such as tumors, moles, warts, etc., on the surface of skin.

At the same time, it can also produce thermal damage. So that the keratin in the stratum corneum is denatured, and the normal structure of the stratum corneum is destroyed. In addition, it can also cause the degeneration of enzyme proteins and affect the enzymatic reaction. Then it leads to moisturizing factors and lipid generation of metabolic disorders, and damages the “brick wall structure” of the skin. As a result, the skin’s ability to resist external stimuli is reduced, and the skin is susceptible to external, ultraviolet and microbial influences, resulting in pigmentation and infection. The skin barrier function indicators such as TEWL, erythema, pigmentation and skin surface capacitance level were improved by applying repair moisturizer after operation. It is similar to non-stripping laser treatment.

1.2.2 Non-exfoliative laser treatment

The theoretical basis of non-exfoliative laser treatment is the selective photothermal effect first proposed by Anderson and Parrish in science in 1983. According to the biological characteristics of the target tissue, a laser with a specific wavelength can be selectively absorbed by the target tissue rather than the surrounding tissue. When the duration of the laser pulse is shorter than or equal to the thermal relaxation time of the target tissue, the energy density is greater than or equal to the light energy density threshold required for tissue damage, which can guarantee the effective treatment of the lesion site. As the heat energy transferred by laser energy is not transferred to the surrounding tissues in time, the damage of laser irradiation to the surrounding normal tissues is minimal. The theory unifies the effectiveness and safety of laser therapy. It is a milestone in the history of laser medicine. Its development has revolutionized the treatment of skin diseases such as port wine stains, hemangioma, telangiectasia, pigmentation and hypertrichosis. The idea that human tissue some ingenious use of pigment content in diseased tissue and normal tissue, select the appropriate laser wavelength in order to make this difference reflected on the absorption of laser energy, thus further reflects on the temperature rise and thermal damage in order to achieve a specific medical purpose, the laser treatment of farewell CuFangXing, nonselective into the accuracy and selectivity. No matter skin damage caused by exfoliative laser or non-exfoliative laser, local inflammatory reaction occurs, initiating the wound repair process, inducing dermal collagen degeneration, stimulating fibroblast proliferation, increasing collagen regeneration, increasing skin moisture content, smoothing the skin surface and accelerating epidermal regeneration.

1.2.3 Fractional laser treatment

Non-exfoliative laser is effective in pigment and blood vessels, but it is not as good as exfoliative laser in skin reconstruction and scar. In 2003, Anderson and Manstein proposed the theory of fractional photothemalysis(FP). He pointed out that the use of a particular kind of laser to produce a group of microscopic treatment zone(MTZ) that can reach a certain depth without peripheral tissue damage. If the skin tissue has a small thermal damage area and enough surrounding normal tissue, the laser damage area is easy to heal quickly without scar formation. The remaining normal tissue ACTS as a “bridge” in the repair process. Hence also known as the fractional laser. The range size of MTZ varies with the density of microarrays. The keratinocytes of normal tissues crawled to MTZ in a short distance, the small wound healed quickly, and the direct damage to the skin barrier was small. Laubach systematically studied the skin pathological changes after the application of Fraxel non-exfoliative lattice laser treatment. 1 hour after treatment, MTZ reached the dermis deeply, with the surface cutin layer intact, the subepidermal fissure appeared, and some blood vessels were damaged non-selectively. After 7 days, the appearance of the epidermis was very healthy, the thickness of the epidermis was normal to slightly thickened, the shape of the epidermis was normal, and there were no cases of skin damage such as poor keratosis or cracks. Hantash observed the pathological changes of human forearm skin after exfoliative CO2 fractional laser. Immediately after treatment, the exfoliation areas of the epidermis and dermis are covered with a thin layer of eschar. After 1 month treatment, normal cuticle formation. The skin is damaged by heat after the fractional laser treatment, and the microepidermal necrotic debris(MEND) containing melanin will appear in the fracture of basal layer in short term. The skin appears bronze-colored erythema, accompanied by edema, dryness, chip removal and other skin barrier damage. Generally, increase the spacing between the dots, apply growth factor or moisturizing repair product after the operation, and relieve for about 1 week.

Exfoliative fractional laser can form small perforation damage in the cuticle of skin, so it has certain advantages in the field of skin transdermal drug delivery. Exfoliative fractional laser can effectively improve the efficacy of basal cell carcinoma, photolinear keratosis and hypertrophic scar, and reduce the drug concentration of methotrexate in the treatment of psoriasis. Although the non-exfoliative fractional laser does not have the direct perforation damage effect, it can interfere the expression of keratin through the photothermal effect to achieve the osmotic effect.

1.3 Photomechanical effect of laser treatment

The mechanical effects of laser irradiation can be divided into two parts: the pressure of the laser’s own radiation pressure on biological tissue, known as the photopressure, called the primary pressure. The biological tissue absorbs the heat expansion and phase transition caused by the strong laser, as well as the pressure caused by ultrasonic wave, shock wave, electrostriction and so on, which is called the secondary pressure. The pressure changes of biological cells caused by laser can change the shape of biological cells and tissues, causing mechanical forces inside or between biological cells and tissues, thus having a huge impact on biological cells and tissues. At present, the photomechanical effect of laser has been successfully used to treat cutaneous vascular and pigmented lesions.When in the treatment of vascular lesions, the temperature of the red blood cells will increase at 107 ℃ per second, it will quickly produce pressure wave, leads to the formation of a vascular rupture and purpura. At the same time, due to the mechanical force of cells, the integrity of keratinocytes is damaged, which leads to a series of clinical manifestations of skin barrier dysfunction, such as erythema, exudation, pigmentation, etc., so the normal function of repairing skin barrier after laser surgery plays a decisive role in the treatment effect.

2. Light adjustionfunctionof laser treatment

Light adjustion function is the abbreviation of photobiomodulation, which refers to the use of laser, luminescent secondary tube or other light source to regulate cell activity through non-photothermal action. The Light adjustion function is thought to be the activation of the energy switching mechanism at the mitochondrial level. The energy absorbed can activate cell function, promote cell proliferation and migration, and regulate cytokine and inflammatory medium levels. This process is similar to electron transport in chloroplasts in plant photosynthesis. Cytochrome by protoporphyrin Ⅸ synthesis, cell pigment molecules, especially on the mitochondrial membrane is mitochondrial cytochrome C oxidase absorb light energy base.The “antenna” molecules of the mitochondrial membrane undergo structural changes after absorbing light, and the ADP is converted into ATP, a process that provides more energy for the cell’s non-mitotic processes. Light adjustion function ACTS on fibroblasts, keratinocytes, white blood cells, macrophages, etc., playing a role in skin aging, wound healing, anti-inflammatory repair, acne and other skin problems. In a clinical trial conducted by Weiss, 90 patients were treated with pulsed leds at 590nm twice a week for 8 weeks. The results showed that the symptoms of photoaging were improved in 90% of the patients with improved skin quality, decreased periorbital wrinkles, and significantly reduced skin erythema and pigment. Takezaki used LED red light (Omnilux, 630nm + 3nm) to irradiate the outer skin of the lower limbs of 6 volunteers once a week for 8 weeks, 105m W/cm2 at 15min each, with an energy density of 95J/cm2. After 8 times of treatment, skin biopsy was taken for qualitative and quantitative PCR. The results showed that both the number of Th-1 and Th-2 increased, and the increase of the latter was more obvious. Skin T cells play an important role in the body’s immune defense system. After bacteria or allergens enter the dermis through the epidermis, they migrate from the lymph nodes to the local skin, playing a positive role in the body’s wound healing. In a clinical trial conducted by Alster, 20 patients received full-face 1550nm non-striping laser resurfacing treatment, and part of the face was irradiated immediately with 590nm LED. The results showed that after 24h, the erythema in the LED treatment area of 20 patients was reduced compared with the control area, among which 6 patients received the high-energy density lattice laser treatment, and the erythema in the LED treatment area was further reduced compared with the control area after 48h. It is suggested that LED dimming can reduce the degree of erythema and shorten the duration of erythema after operation.In another clinical trial using intense pulsed light (IPL) for the treatment of photoaging, 15 patients were treated with 590nm LED immediately on one side of the face after IPL, and changes in erythema and discomfort were observed after 24 hours.The results showed that LED dimming could promote the redness of erythema after IPL operation and reduce the discomfort after operation.

3. Epilogueof laser treatment

Laser treatment of various skin diseases is a “double-edged sword”, which often affects the barrier structure and function of the skin.Skin barrier repair is a very complex process. Selecting the appropriate laser equipment, the appropriate energy density, pulse width and spot diameter, and mastering the terminal response of various lasers to treat different skin diseases can reduce the damage of skin barrier to the greatest extent.In addition to routine ice compress, moisturizing and sun protection, postoperative skin repair products and dressings, or phototoning treatment can accelerate the healing of skin wounds, and skin barrier repair is more effective.Therefore, the changes and repair of the skin barrier during laser treatment are of great guiding significance for clinicians in alleviating the adverse reactions after laser treatment.

DianFu Star uses reactive oxygen radicals (including thermal energy, ultraviolet radiation, charged particles, neutral reactive groups such as mono oxygen, ozone, nitrogen oxides, hydroxyl radicals, and high voltage electric fields) generated during glow discharge.Through high speed granule flow, it can penetrate germ cells instantly, damage cell wall structure, increase cell permeability or rupture, eliminate inflammation and sterilize, and induce pathological cell apoptosis.At the same time, highly active particles act on human skin to supplement the active nitrogen and oxygen particles of cells and increase cell activity.Strengthen the absorption of nutrients, stimulate the regeneration of cell collagen, eliminate wrinkles, gradually dissolve melanin, repair damaged cells, deeply purify the skin and activate cells, so as to achieve the effect of freckle removal.Regulate the function of cells from inside out, reduce the sensitivity of skin, fundamentally improve and solve various problems of skin.