Research progress of hyaluronic acid in the repair of sensitive skin barrier

In recent years, the occurrence of sensitive skin is increasing. The generation of sensitive skin is often related to the dysfunction of skin barrier. Abnormal skin barrier function can cause discomfort to sensitive skin, mainly including prickling, scorching, tending and itching, and prone to recurrent attacks, which seriously affect the quality of life of the patients. Studies have shown that hyaluronic acid can repair the skin barrier of sensitive skin and improve the sensitive condition of skin, so it is widely used in skin barrier repair. This text will summarize the research status of hyaluronic acid for sensitive skin barrier repair in recent years and pathogenesis of sensitive skin and the mechanism of hyaluronic acid repairing of the skin barrier are expounded and discussed, and the theoretical basis for clinical application and related product development is provided.

1 sensitive skin overview

1.1 Definition of sensitive skin

The definition of sensitive skin is not uniform. Some scholars believe that sensitive skin is a kind of skin situation, which is more sensitive to external stimuli and more responsive than normal skin. That is, the skin care products and changes in the external environment can not be tolerated, so sensitive skin can also be defined as hyperreactive skin. Some scholars believe that sensitive skin is the subjective discomfort caused by skin exposure to external stimuli, including drying, tightness, tingling, pruritus, and burning sensation. To sum up, sensitive skin is a highly sensitive skin condition, and the skin in this state is easily stimulated by various physical and chemical factors, and the skin feeling discomfort (such as prickling, burning, tending, itching, etc.) is a skin disease that is not suitable for clinical symptoms. The cause of the disease is unknown, the clinical manifestation is mainly subjective feeling abnormality, the objective clinical signs are missing or slight, and they are characterized by high sensitivity, poor tolerance and high reactivity.

1． 2 Factors affecting sensitive skin

The factors causing sensitive skin include endogenous factors and exogenous factors. Endogenous factors are not only related to sex, age and race, but also related to skin diseases such as seborrhea dermatitis, rosacea, atopic dermatitis (AD), psoriasis, acne, neurosensory and dermatosis phobia. The exogenous stimulant factors include: (1) environmental factors such as air pollution, seasonal change, exposure time, ultraviolet radiation intensity, etc.; (2) chemical factors, including daily use of cosmetics, hair dyes, spices and insecticides; 3. Lifestyle, such as frying and stimulating diet, alcohol, and caffeine. Caffeine, excessive use of body care products and excessive shower.

1． 3 The mechanism of skin barrier damage in sensitive skin

At present, it is considered that the occurrence of sensitive skin is a complex process involving skin barrier, nerve blood vessel and immune inflammation. Under the interaction of internal and external factors, the function of the skin barrier is damaged and the signal of sensory nerve afferent is increased, which causes the response of the skin to the external stimuli increased and causes the immune response to the skin.

The damage of the skin barrier function presents the incomplete structure of the skin cuticle and the imbalance of the lipid content among the epidermal cells, which can lead to the reduction of ceramide content. The skin physiological index test shows that the skin water loss rate (trans epidermal water loss, TEWL) increases and the water content of the cuticle decreases, which suggests that the sensitive skin barrier function is damaged. The skin surface temperature too low or too high (< 34 or > 42 C) delays the repair of the skin barrier, so the ambient temperature can cause or aggravate the sensitive skin.

It is considered that the incompleteness of the cuticle of the skin leads to the weakening of the protective ability of the skin nerve endings, the increase of the density of the nerve fibers and the increase of the sensory nerve. These three interact with each other, causing skin sensory nerve dysfunction, which shows that temperature changes can cause burning, pricking and itching symptoms of sensitive skin. Some researchers also found that neurologic dysfunction promoted the release of local neurotransmitters P, vasoactive intestinal peptide, neurotensin and trypsin, and it also lead keratinocytes forming in the vicinity of the sensory nerve endings , mastocyte releasing IL-23 and IL-31, and activation of antigen presenting cells and T cells. It could lead to skin immune and inflammatory reaction, and erythema and swelling appear on the skin.

1． 4 Clinical manifestation of sensitive skin

According to the consensus of Chinese experts on sensitive skin, the clinical manifestations of sensitive skin are divided into subjective symptoms and objective signs,.The subjective symptoms are usually caused by physical, chemical and mental stimulation of the skin with different degrees of scorching, prickling, itching, and tightness. It lasts for several minutes or even hours. It is not tolerable to ordinary skin care products. The objective physical appearance of sensitive skin is mostly normal, and the facial skin of a few people can appear flaky or diffuse flashes, erythema and telangiectasia, which can be accompanied by drying and small scales.

2 Hyaluronic acid and its biological function in the Department of Dermatology

2． 1 Overview of hyaluronic acid HA

HA, also known as hyaluronic acid, is widely distributed in connective tissue such as human cells, eye glass balls and synovial fluid. It is also one of the main matrix components of skin skin and dermis. It can promote the proliferation and migration of epidermal keratinocytes and promote wound healing. Hyaluronic acid in the dermis provides space and nutrition for collagen and elastic fibers, forming a skin scaffold together, and is an important extracellular matrix to maintain the stability, fusion and elasticity of skin tissue.

2． 2 Biological function of hyaluronic acid in Dermatology

2． 2． 1 The moisturizing effect of HA.

Hyaluronic acid on the skin depends mainly on the size of the molecular weight. The greater the molecular weight, the stronger the moisture retention; the smaller the molecular weight, the weaker the moisture retention. The large molecular weight HA is mainly used for skin moisturizing,.The HA coated on the skin surface, can quickly form a layer of breathable membrane on the skin surface, soften the skin cuticle, and it can further enhance the skin cuticle to the active material absorption and utilization, make the skin smooth.

2． 2． 2 The anti aging function of HA.

The main factor of skin aging is that the ultra – oxygen free radicals are produced by ultraviolet radiation, and HA has the function of removing oxygen free radicals. Therefore, it can delay skin aging and protect the skin from injury. Skin is exposed to sun exposure to red, burning, and desquamation, and it can use cosmetics containing HA to promote the proliferation and differentiation of epidermal cells, and use HA deoxidizing free radicals to help the recovery of the injured part of the skin. Sunscreen often adds UV absorbers to achieve sunscreen purposes, because HA can greatly reduce the transmittance of ultraviolet rays and repair skin damage caused by a small amount of ultraviolet light through.

2． 3 HA is involved in the healing of skin injury.

Skin injury can be divided into inflammatory stage, proliferative stage and reconstructive stage. In the inflammatory period, the synthesis of long chain HA is increased. Its water absorption leads to the expansion of tissue around the wound and the porous structure suitable for cell migration to the injured part, and can inhibit the migration of neutrophils and alleviate the inflammatory reaction. In proliferation period, short chain HA can promote the migration of fibroblasts to traumatic tissue, fibroblasts produce collagen and glycosaminoglycan (GAG), and construct a new extracellular matrix (ECM); HA also promotes the proliferation and migration of angiogenesis and keratinocytes. During reconstruction, HA promotes normal and pathological scar formation, and also has bacteriostatic and anti-inflammatory effects.

3 Study of hyaluronic acid on skin barrier of sensitive skin

3． 1 Hyaluronic acid and skin physical barrier

Impaired skin barrier of sensitive skin increaseds epidermal water loss (TEWL), dry skin, desquamation, and sensitivity. Hyaluronic acid is combined with protein to form a molecular weight protein polysaccharide molecule, forming hyaluronic acid protein water gel structure. It is an important component to maintain the moisture of the skin tissue. It can keep skin moisture and prevent chap and wrinkles. For external use, skin has water retention, lubricity, film-forming ability, epithelial regeneration and safety. Professor Min Sun used it to treat 98 cases of facial seborrheic dermatitis with hyaluronic acid moisturizing skin care. It was found that the after 4 weeks treatment,the average severity score,the water content and skin water loss of facial erythema, desquamation, papule and pruritus were significantly improved, suggesting that the external use hyaluronic acid has super strong moisturizing effect.

3． 2 The moisturizing effect of hyaluronic acid and sebum membrane

The lack of linoleic acid in the sebum membrane makes the permeability of the stratum corneum abnormal. The lack of linoleic acid sebum increased the loss of water through epidermis, showing dry skin and desquamation, and the skin’s anti-inflammatory ability was reduced. Sensitive skin is often destroyed by fatty acids such as linoleic acid in sebum membrane. The hydroxyl group and other polar groups of hyaluronic acid can form hydrogen bonds with water molecules and combine with large amounts of water, because they have good film forming properties. It can form a uniform film on the skin surface to reduce the evaporation of moisture on the skin surface, so as to provide a good moisturizing environment for the skin. Professor Liu Fuhua and other clinical observations confirm that hyaluronic acid repair biofilm has the function of restoring skin barrier and good moisturizing effect.

The skin barrier damaged mouse model and Superficial dermis injury after laser surgery models established by Professor Xu Liangheng proved that hyaluronic acid dressing could promote the repair of the skin barrier.

In addition, it is also shown that the protective film of sodium hyaluronate, which is formed by hyaluronic acid, can resist the harm of adverse environment, bacteria and sensitization source, keep the local moist environment, protect the micro wound, reduce the inflammatory reaction, promote the skin barrier function and improve the skin tolerance.

3． 3 Hyaluronic acid and the antioxidation of local skin

If the skin is exposed to ultraviolet light for a long time, the linoleic acid of sebum will be significantly reduced, thereby damaging the skin barrier. This will induce the proliferation of keratin (K6 and K16) and the activation of inflammation related keratin (K17), thereby inducing inflammatory reaction. It also confirms that the impaired skin barrier is due to the degeneration of keratin in the stratum corneum, and the destruction of normal structure. And sunburn and melanin increase, easy to form pigmentation, such as failure to deal with may lead to scarring, pigmentation, long-term facial sensitivity and other issues. Hyaluronic acid can prevent the formation of free radical formation related enzymes in cells, reduce the formation of free radicals, and play an important role in preventing free radical destruction of cell structure, producing lipid peroxidation and causing body senescence. Small molecular weight hyaluronic acid has the functions of anti-inflammatory, inhibiting the generation of bacteria and keeping skin clean.

3． 4 Hyaluronic acid and skin wound healing

There is inflammatory cell infiltration around the dermal vessels of sensitive skin, and edema and intercellular edema in the epidermis. The clinical manifestations were erythema, swelling, and even blister. Hyaluronic acid in the dermis provides space and nutrition for collagen and elastic fibers. It is an important extracellular matrix to maintain the stability, fusion and elasticity of skin tissue. It has anti – inflammatory effect, which can regulate collagen synthesis, promote wound healing, and provide a favorable environment for repair of sensitive skin barrier and wound healing. Neuman and so on will apply hyaluronic acid water cosmetic to smear on the surface of mild skin burn, relieve pain and accelerate healing of injured parts. This further confirmed that the external hyaluronic acid can regulate the wound hypercontraction and reduce the scar formation; in vitro, Prosdocimi and other experiments show that hyaluronic acid has a good repair effect on the apoptosis of skin cells induced by ethanol. In addition, hyaluronic acid can penetrate the skin through the normal skin barrier and directly promote cell growth, differentiation, reconstruction and repair. It also has the effect of inhibiting inflammatory reaction, promoting angiogenesis, improving intermediate metabolism, promoting nutrition absorption, increasing skin elasticity and other repair and beauty care.

4.Conclusion and Prospect

Sensitive skin is a common and multiple skin disorder that affects the quality of life of patients. Because of the unclear mechanism, the difference between the induced factors and the clinical manifestations is very large, which brings great confusion to the effective clinical treatment. The treatment and nursing of sensitive skin are aimed at repairing skin barrier function, reducing skin sensitivity and inflammatory reaction, and improving skin tolerance. Hyaluronic acid, as a natural moisturizing factor, can obviously improve the skin permeability barrier function and increase the water content of the cuticle, restore the skin barrier and promote the healing of the wound. Therefore, hyaluronic acid is a safe and effective method for the treatment of sensitive skin barrier. There are few basic or molecular biological studies related to the skin barrier and hyaluronic acid, which need further development and research, and can also provide effective evidence for the development of more sensitive cosmetics suitable for sensitive skin.

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