Moisturizing Effect of Hyaluronic Acid and Plant Extracts

Skin Moisturizing Mechanism

The skin consists of epidermis, dermis and subcutaneous tissues.

The epidermis is a self-stabilizing and self-renewing tissue, and water plays a key role in the orderly differentiation and desquamation of the skin, as well as giving it plasticity and flexibility. The stratum corneum is the outermost region of the skin epidermis, and although it contains only about 15% water, it plays a key role in the skin barrier as well as in moisturizing function.

The dermis is not only the main water storage site of the skin, but also the site of nutrient metabolism and exchange. The dermis is the thickest of the three layers of the skin, and its water content accounts for about 70% of the entire skin. The collagen fibers in the dermis can store a large amount of water. In addition, mucopolysaccharides in the dermal matrix such as hyaluronic acid and chondroitin sulfate have a strong hydration capacity. Hyaluronic acid holds water in the tissues, thus changing the volume and compressibility of the dermis and affecting cell proliferation and differentiation as well as tissue repair. The dermis gets its water from subcutaneous tissues and capillaries, etc. When the dermis loses its filling, especially the reduction of hyaluronic acid, it leads to disorganization, thickening and collagen fragmentation of collagen fibers, leaving the entire skin with a disorganized elastic fiber, a phenomenon that changes irreversibly with age.

Skin Moisturization Methods

Endogenous Moisturization The moisture content of the skin is related to many hydration components in the epidermis as well as in the dermis. The outermost layer of the skin, the stratum corneum, acts as a barrier between the external environment and the body. This barrier protects against moisture loss and the intrusion of foreign objects, among other things. The stratum corneum is essential for maintaining the moisture content of the skin surface. In addition, ceramides are important structural components of the skin's epidermis and play an important role in maintaining the relative stability of the internal environment. The dermis plays a nutritional, structural, vascular support and wound repair role for the epidermis. Collagen fibers in the dermis not only store large amounts of water, but are also tough and tensile, giving the skin resilience and tone to resist external mechanical damage. Hyaluronic acid in the dermis constitutes the main protective barrier of the underlying tissues against the external environment, which not only binds with water to prevent water loss, but also has a role in scavenging free radicals, etc.

Exogenous moisturizing Depending on the sealing and moisturizing properties of exogenous moisturizers, their moisturizing hydration mechanisms are different: sealing components produce a thin layer of oil on the skin to prevent water evaporation; moisturizing components absorb water and retain water in the skin. Different moisturizers have different hydration capacities and have different effects on the degree of skin hydration. Water-soluble humectants in moisturizers temporarily increase skin hydration by absorbing into the epidermis. Among them, hyaluronic acid is considered to be an ideal natural moisturizing factor and is widely used in cosmetics. Lipids and other ingredients in moisturizers form a film on the skin surface to reduce transepidermal water loss, and lipids and other ingredients penetrate into the skin, cross the stratum corneum and mix with epidermal lipids to relieve dry skin and provide skin protection and physiological lipids.

Plant extracts with moisturizing effect

In plants, water-soluble components such as polysaccharides and glycosides have sugar groups in their structures, which have good water absorption and water retention properties through hydrogen bonding; the phenolic hydroxyl structures in flavonoids and polyphenols also have the ability to absorb and retain water by binding water through hydrogen bonding; and plant oils mainly retain water by forming a thin layer on the skin to prevent skin dryness.

Polysaccharides Polysaccharides are widely found in plants. The monosaccharide units in plant polysaccharides are interconnected to form a branched or linear structure, but their main chains are usually glucan, fructan, xylan, mannan or galactan, or polymers of two or more monosaccharides. The branched structures of polysaccharides show great diversity. The structures of plant polysaccharides usually have a large number of hydroxyl groups, which give them good hydration ability through hydrogen bonding. In addition, polar groups of plant polysaccharides, such as carboxyl groups, can also be bound to water molecules through hydrogen bonds. Therefore, most of the plant polysaccharides have the properties of moisture absorption and water retention. Plant polysaccharides have been widely used as humectants in various cosmetic products. The moisturizing ability of plant polysaccharides is mainly influenced by the structure, composition and molecular weight of their glycosyl groups. Many plant extracts of polysaccharides can improve the moisturizing effect of skin even at low concentration state, which in turn can reduce water loss.

Oils Plant oils form a hydrolipidic film on the surface of the skin, which not only has a moisturizing effect, but also makes the skin water resistant. Vegetable oils strengthen the skin barrier and influence the reconstruction of the stratum corneum, preventing water loss from the skin and normalizing the sebaceous glands. Vegetable oils also have an important impact on the normal appearance and function of the skin. Vegetable oils are used in a wide variety of cosmetic products, including creams, lotions, conditioners, hair creams, beauty masks and lip balms.

Saponins Saponins are widely distributed in higher plants and have a rich structural and functional diversity. Based on different glycoside structures, saponins are classified into triterpene saponins and steroidal saponins. Triterpene saponins are mainly found in dicotyledons, while steroidal saponins are mainly found in monocotyledons. Most saponins are a combination of hydrophobic glycosides and hydrophilic glycosyl groups, so saponins have a high degree of amphiphilic affinity and have moisturizing, foaming and emulsifying properties.

Flavonoids Flavonoids are usually present in multiple phenolic hydroxyl structures and in many plants are bound to glycosyl groups to form flavonoid glycosides. Flavonoid components of plants are not only hygroscopic, but also have a wide variety of biological activities. The addition of flavonoid components to cosmetics helps restore elasticity and radiance to dry, sagging skin. The flavonoid component quercetin is widely found in plants. Chamomile extract containing quercetin enhances skin hydration, repairs dry and dehydrated skin, and is more effective in soothing sensitive skin. Quercetin also has antioxidant, anti-inflammatory, anti-allergic and anti-aging effects. The combined antioxidant/anti-inflammatory effect of quercetin is also beneficial for wound healing. Many flavonoid-rich plant extracts such as mother chrysanthemum, pear fruit cactus and mullein extracts have biological activities such as antioxidant, anti-aging and anti-inflammatory in addition to moisturizing.

Polyphenols Polyphenolic compounds are also widely found in plants. Polyphenols exhibit certain moisturizing effects because they contain hydrophilic phenolic hydroxyl groups that bind to water through hydrogen bonds, reducing water loss from the skin. The main component of tea extract is tea polyphenol, which is a typical polyphenol with moisturizing effect. Tea polyphenols not only have moisturizing, sunscreen, tyrosinase inhibition and anti-photoaging effects, but also promote the differentiation of keratin-forming cells and the formation of skin barrier, and promote wound healing. Besides, tea polyphenols can also displace the water-rich skin tissue fluid and reduce the viscosity of the intercellular space. Tea polyphenols have a better ability to absorb moisture and retain water at relatively low humidity; when used in cosmetic formulations, they work better in relatively dry environments.

In addition, the composition of many plant extracts is complex, with the presence of multiple types of natural products. For example, the main components in helianthus extract and onychophyll extract are saponins, polyphenols and flavonoids, which not only have moisturizing effects and maintain the skin barrier, but also have anti-inflammatory, antioxidant and tyrosinase inhibiting activities.

In summary, in addition to vegetable oils, the main components of plant extracts with moisturizing effects are polysaccharides, saponins, flavonoids and polyphenols. The structure of these components is characterized by polyhydroxy or polyphenolic hydroxyl groups, which produce moisturizing effects mainly through hydroxyl or phenolic hydroxyl groups forming hydrogen bonds to bind water and maintain water. The more hydroxyl groups in the structures of water-soluble polysaccharides and saponins in plant extracts, the stronger their ability to bind water is usually. These components in plant extracts usually have antioxidant and anti-inflammatory effects in addition to their moisturizing effect.

Contect ZANCHENG to get more information.