In plants, there are sugar groups in the structure of water-soluble components such as polysaccharides and glycosides, which have good hydration and water absorption and water retention characteristics through hydrogen bonds; the phenolic hydroxyl structures in flavonoids and polyphenols also through hydrogen bonds Binds moisture, giving it the ability to absorb and retain moisture; whereas vegetable oils retain moisture primarily by forming a thin layer of oil on the skin, preventing dryness of the skin.

Polysaccharide

Polysaccharides are widely found in plants. The monosaccharide units in plant polysaccharides are connected to each other to form branched or linear structures, but the main chain is usually glucan, fructan, xylan, mannan or galactan, etc., or two or more A polymer of monosaccharides. The branched-chain structures of polysaccharides exhibit great diversity. There are usually a large number of hydroxyl groups in the structure of plant polysaccharides, which have good hydration ability through hydrogen bonds. In addition, polar groups such as carboxyl groups of plant polysaccharides can also combine with water molecules through hydrogen bonds. Therefore, most plant polysaccharides have the properties of hygroscopicity and moisture retention. Plant polysaccharides have been widely used in various cosmetics as humectants. The moisturizing ability of plant polysaccharides is mainly affected by their sugar base structure, composition and molecular weight. The polysaccharides of many plant extracts can improve the moisturizing effect of the skin even at low concentrations, and can reduce water loss.

β-glucan is a class of macromolecular cell wall polysaccharides widely present in plants and fungi, composed of β-glycosidic linkages of glucose groups. β-glucan is an effective moisturizing ingredient in cosmetic formulations, which can relieve dry skin and atopic diseases, and reduce itching caused by bacterial infections. β-glucans from different sources have different glycosidic bonds and their ratios and different three-dimensional structures, etc., which make β-glucans have different properties and biological activities, such as promoting wound healing, anti-inflammatory and anti-allergic. Oat β-glucan is composed of glucose groups connected by β-1,4 and 1,3 glycosidic bonds. The mixed chain structure of oat β-glucan destroys the uniform structure of β-D-glucan, making Oat β-glucan has good water solubility and moisture retention; while high molecular weight oat β-glucan has high viscosity.

Aloe vera extract is a moisturizing raw material widely used in cosmetics. Many moisturizing cosmetics contain aloe vera extract. The main active ingredient of aloe extract is aloe polysaccharide. In addition to its good moisturizing effect, aloe polysaccharide has certain viscosity and gel properties, and it also has a good effect on skin wound healing and dry skin repair ; In addition, aloe polysaccharides also have certain effects on atopic dermatitis. The polysaccharides in cactus extract are composed of neutral polysaccharides, acid polysaccharides and acid glycoproteins. Cactus polysaccharides can not only hydrate, absorb and maintain skin moisture, but also have anti-inflammatory and wound healing effects. Most of the water-soluble plant polysaccharides, such as astragalus polysaccharides, licorice polysaccharides, dendrobium polysaccharides and fire ginseng polysaccharides, have good hydration and water absorption characteristics, and have good moisturizing and film-forming properties. Moisturizing, etc. have a very good effect, but also have antioxidant activity and other effects.

There are also a large number of polysaccharides in seaweed, and the types of polysaccharides in different seaweeds are also different. Many seaweed polysaccharides have good hydration and hygroscopicity and the ability to retain water. Low-molecular-weight polysaccharides from some macroalgae exhibit a high ability to absorb and retain water compared to hyaluronic acid. Alginic acid is a polysaccharide from brown algae. Alginic acid can be used not only as a moisturizer, but also as a stabilizer and gelling agent in cosmetics. Alginic acid can quickly absorb water, and can also form a protective moisturizing complex through ion-ion interaction. It has good hygroscopic and hydrating properties, thereby helping to increase skin moisture and improve skin elasticity. In the presence of divalent cations, alginate has good gel properties and ion chelation; in the mask formulated with alginate, alginate forms a flexible film with better adsorption to the skin. In addition, algae extracts such as Rhizoctonia solifolia extracts have a moisturizing effect similar to hyaluronic acid, and the moisturizing effect is good and long-lasting; fucoidan improves skin elasticity through hydration; hydroxyl groups in sargassum polysaccharides and water form The intermolecular hydrogen bond promotes its water absorption, and the moisturizing effect of Sargassum polysaccharide increases with the increase of sulfate content; Ulva polysaccharide not only has moisturizing properties, but also has anti-oxidation and anti-coagulation activities.

Oil

Vegetable oil can form a hydrolipidic film on the surface of the skin, which not only has a moisturizing effect, but also makes the skin waterproof. Vegetable oils strengthen the skin barrier and influence the reconstruction of the stratum corneum, prevent skin moisture loss and normalize the sebaceous glands. Vegetable oils also have an important influence on the normal appearance and function of the skin. Vegetable oils are widely used in a variety of cosmetics, including face creams, lotions, hair conditioners, hair conditioners, beauty masks, and lipsticks.

Unsaturated fatty acids are the main components of vegetable oils. In addition to unsaturated fatty acids, wheat germ oil is also rich in vitamins. Wheat germ oil is added to cosmetic formulas to form a closed layer on the skin, prevent moisture loss, increase moisturizing effect, and also promote skin regeneration for dry and rough skin. effect. In addition, wheat germ oil works better synergistically with some plant extracts, which is very effective in preventing dry skin. Many vegetable oils not only have moisturizing effect, are easily absorbed by the skin, have good spreading properties, but also have various biological activities. Coconut oil is a mild moisturizer; coconut oil can increase the expression levels of aquaporin AQP3, integrin and filaggrin, which play a role in keratinocyte differentiation and skin barrier, thereby changing the skin barrier function; coconut oil It is compounded with olive oil to slow down the loss of moisture through the epidermis by sealing, and has a better effect on protecting the skin; coconut oil is used as an emollient, and is also one of the indispensable oils for handmade soaps and some detergents. Seabuckthorn oil in cosmetic formulations not only has moisturizing effect, but also has the effect of skin repair and regeneration, and can also protect, regenerate and soften the cuticle, relieve inflammation, and ensure the stability of the structure between skin cells; seabuckthorn oil is suitable for dry, rough, peeling , itchy or irritated skin. Shampoos and conditioners that add sea buckthorn oil can promote the regeneration of damaged hair and restore the elasticity and smoothness of the hair. In addition, raspberry oil is a good base oil for cosmetics, which not only promotes the hydration of the skin and maintains moisture, avoids the evaporation of epidermal water, but also strengthens the lipid barrier of the epidermis, improves the sebaceous glands, and is suitable for some skin diseases such as silver Psoriasis and rosacea. Grape seed oil contains a large amount of omega-6 fatty acids, which can regenerate the lipid barrier of the epidermis for dry skin and prevent excessive water loss; it can improve acne and normalize sebaceous glands for oily and seborrheic skin.

Saponins

Saponins are widely distributed in higher plants with rich structural and functional diversity. According to different aglycon structures, saponins are divided into triterpene saponins and steroidal saponins. Triterpene saponins are mainly found in dicots whereas steroidal saponins are mainly found in monocots. Most saponins are the combination of hydrophobic aglycon and hydrophilic sugar group, which makes saponins have high amphoteric affinity, and have moisturizing, foaming and emulsifying properties.

The main active ingredients in Centella asiatica extract are pentacyclic triterpene saponins such as madecassoside. Centella asiatica extract is widely used in cosmetics, and has the functions of moisturizing, promoting skin wound healing, anti-inflammation and anti-oxidation; the emulsion of centella asiatica extract compounded with hyaluronic acid and glycerin can produce lasting hydration and moisturizing to the skin effect while improving the skin barrier function. The main active ingredient of ginseng extract is the tetracyclic triterpene saponin ginsenoside. Ginsenosides not only have a good water absorption and moisturizing effect on the skin, but also can stimulate skin regeneration and wound healing by increasing the proliferation and migration of keratinocytes, repair the skin barrier, and have whitening and anti-wrinkle effects. In addition, extracts from many plants such as licorice, pansy, terrestris and quilan are mainly saponins. These saponins combine with water molecules through hydrogen bonds to absorb water and prevent water loss, which helps to moisturize the skin; it can also repair the skin barrier and maintain the function of the stratum corneum, and has obvious anti-inflammatory and antibacterial properties.

Flavonoids

Flavones usually have multiple phenolic hydroxyl structures, and flavones in many plants combine with sugar groups to form flavone glycosides. Plant flavonoids not only have a certain hygroscopicity, but also have a variety of biological activities. Adding flavonoids to cosmetics can help restore the elasticity and luster of dry and sagging skin. Quercetin, a flavonoid, is widely found in plants. Chamomile extract containing quercetin can enhance the moisturizing effect of the skin, repair dry and cracked skin and balance oil secretion, and the effect of soothing sensitive skin is more obvious. Quercetin promotes the expression of tight junction proteins in a dose-dependent manner, thereby enhancing the tightness of cell junctions, maintaining the integrity of the skin barrier and regulating water dynamic balance, preventing skin dehydration and reducing skin sensitivity; quercetin combined with essential oils Formulated with a synergistic effect, it promotes moisturizing effect on the skin. Quercetin also has antioxidant, anti-inflammatory, anti-allergic and anti-aging effects. The combined antioxidant/anti-inflammatory effects of quercetin also benefit wound healing. Many flavonoid-rich plant extracts, such as chamomile, pomegranate and moso bamboo extracts, have antioxidant, anti-aging and anti-inflammatory biological activities in addition to moisturizing effects.

Polyphenols

Polyphenolic compounds are also widely found in plants. Because polyphenols contain hydrophilic phenolic hydroxyl groups, they combine with water through hydrogen bonds to reduce skin moisture loss and exhibit a certain moisturizing effect. The main component of tea extract is tea polyphenols, and tea polyphenols are typical polyphenols with moisturizing effect. Tea polyphenols not only have the functions of moisturizing, sun protection, inhibiting tyrosinase and anti-photoaging, but also can promote the differentiation of keratinocytes and the formation of skin barrier, and promote wound healing. In addition, tea polyphenols can also displace the moisture-rich skin interstitial fluid and reduce the viscosity of the intercellular space. Tea polyphenols have better moisture absorption capacity and water retention capacity when the humidity is relatively low; that is, when used in cosmetic formulations, their effect is better in a relatively dry environment. Proanthocyanidins are a kind of polyphenolic polymer, and its phenolic hydroxyl group has strong hydrophilicity, which can absorb water, maintain the water content of the stratum corneum, and produce moisturizing effect. For water-soluble polyphenolic compounds in plant extracts, the more phenolic hydroxyl groups in the polyphenolic structure, the stronger the hydration ability and the more obvious the moisturizing effect.

In addition, the composition of many plant extracts is relatively complex, and there are many types of natural products. For example, the main components of horse chestnut extract and Hypericum perforatum extract are saponins, polyphenols and flavonoids, which not only have moisturizing effect, maintain skin barrier, but also have anti-inflammatory, anti-oxidation and inhibition of tyrosinase activity.

To sum up, in addition to vegetable oil, the main components of plant extracts with moisturizing effect are polysaccharides, saponins, flavonoids and polyphenols. The structural characteristics of these ingredients are polyhydroxyl or polyphenolic hydroxyl groups, which mainly form hydrogen bonds to bind moisture and maintain moisture through hydroxyl or phenolic hydroxyl groups to produce moisturizing effects. The more hydroxyl groups in structures such as water-soluble polysaccharides and saponins in plant extracts, the stronger their ability to bind water is usually. In addition to moisturizing effects, these ingredients in plant extracts usually have antioxidant and anti-inflammatory effects. Although plant extracts have many advantages as moisturizing ingredients, there are still some problems: First, except for vegetable oils, the content of moisturizing ingredients in plant extracts is usually not very high, so it is necessary to refine these moisturizing ingredients Improve its moisturizing effect; Second, there are differences in the absorption effect of plant extracts, especially macromolecular polysaccharides, as well as polysaccharide-based saponins and polyphenol polymers, so it is necessary to use different methods or dosage forms to solve their effects on the skin. permeability and bioavailability, etc. The application of plant extracts in moisturizing products still needs to be continuously explored and improved.