Plant extracts in cosmetics

In plants, there are sugar groups in the structure of water-soluble components such as polysaccharides and glycosides, which can absorb and maintain water through hydrogen bonding; The phenolic hydroxyl structure in flavonoids and polyphenols also combines water through hydrogen bonds, thus having the ability to absorb and maintain water; Vegetable oil can keep moisture and prevent skin from drying by forming a thin layer of oil on the skin.
Polysaccharide
Polysaccharides are widely found in plants. The monosaccharide units in plant polysaccharides are interconnected to form branched or linear structures, but their main chains are usually dextran, fructan, xylan, mannan or galactose, or polymers of two or more monosaccharides. The branched chain structure of polysaccharides shows great diversity. There are a lot of hydroxyl groups in the structure of plant polysaccharides, which have good hydration ability through hydrogen bonding. In addition, the polar group of plant polysaccharides, such as carboxyl, can also combine with water molecules through hydrogen bonds. Therefore, most plant polysaccharides have the characteristics of moisture absorption and water retention. As a humectant, plant polysaccharides have been widely used in various cosmetics. 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 skin and reduce water loss even at low concentrations.
Oil, saponin
Vegetable oil can form a water-lipid film on the surface of the skin, which not only has the moisturizing effect, but also makes the skin waterproof. Vegetable oil can strengthen skin barrier and affect the reconstruction of cuticle, prevent skin moisture loss and normalize sebaceous glands. Vegetable oil also has an important impact on the normal appearance and function of skin. Vegetable oil is widely used in various cosmetics, including face cream, lotion, conditioner, hair moisturizer, beauty facial mask and lipstick.
Saponins are widely distributed in higher plants with rich structural and functional diversity. According to different aglycone structures, saponins are divided into triterpenoid saponins and steroidal saponins. Triterpene saponins mainly exist in dicotyledonous plants, while steroidal saponins mainly exist in monocotyledonous plants. Most saponins are the combination of hydrophobic aglycones and hydrophilic sugar groups, so saponins have high amphoteric affinity and have the characteristics of moisturizing, foaming and emulsifying.
flavone
Flavonoids usually have multiple phenolic hydroxyl structures, and flavonoids in many plants combine with sugar groups to form flavonoid glycosides. Flavonoids in plants not only have certain hygroscopicity, but also have a variety of biological activities. Adding flavonoids in cosmetics can help restore the elasticity and luster of dry and loose skin. Quercetin, a flavonoid component, widely exists in plants. Chamomile extract containing quercetin can enhance the moisturizing effect of the skin, repair the dry and cracked skin, and relieve the 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 to wound healing. Many plant extracts rich in flavonoids, such as fructus aurantii, chrysanthemum, pear fruit cactus and phyllostachys pubescens, have antioxidant, anti-aging, anti-inflammatory and other biological activities in addition to moisturizing.
polyphenol
Polyphenol compounds also widely exist in plants. Polyphenols, which contain hydrophilic phenolic hydroxyl groups, combine with water through hydrogen bonds to reduce skin moisture loss and show a certain moisturizing effect. The main component of tea extract is tea polyphenol, which is a typical moisturizing polyphenol. Tea polyphenols not only have the effects of moisturizing, sunscreen, tyrosinase inhibition and photoaging, but also promote the differentiation of keratinocytes and the formation of skin barrier, and promote wound healing. In addition, tea polyphenols can also displace the skin tissue fluid rich in water and reduce the viscosity of intercellular space. Tea polyphenols have better hygroscopicity and water retention capacity when the humidity is relatively low; When used in cosmetics formula, it works better in a relatively dry environment.
In addition, the components of many plant extracts are complex and there are many types of natural products. For example, the main components in the extracts of Aesculus chinensis and Hypericum perforatum are saponins, polyphenols and flavonoids, which not only have the moisturizing effect, maintain the skin barrier, but also have the effects of anti-inflammatory, antioxidant and tyrosinase inhibition.
To sum up, in addition to vegetable oil, the main ingredients with moisturizing effect in plant extracts are polysaccharides, saponins, xanthones and polyphenols. The structural characteristics of these components are polyhydroxy or phenolic hydroxy, which mainly form hydrogen bonds through hydroxyl or phenolic hydroxy to combine water and maintain water to produce moisturizing effect. The more hydroxyl groups in the structure of water-soluble polysaccharides and saponins in plant extracts, the stronger their ability to bind water. In addition to moisturizing effect, 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, in addition to vegetable oil, the content of moisturizing ingredients in plant extracts is usually not very high, so it is necessary to refine these moisturizing ingredients to improve their moisturizing effect; Second, there are differences in the absorption effects of plant extracts, especially the macromolecular polysaccharides, as well as the glycosides and polyphenol polymers of polysaccharides. Therefore, it is necessary to adopt different methods or dosage forms to solve the problems of skin permeability and bioavailability. The application of plant extracts in moisturizing products still needs to be explored and improved.
(The article is excerpted from the Chinese Medical Journal and the Science of Daily Cosmetics, Issue 5, 2021)