Post by chenhongxia on Aug 15, 2008 11:41:31 GMT 7
The most obvious target of cleansing is the outermost layer of the skin, the keratinizing epithelium. It is a cornified (hardened) cell envelope and it has an extremely tough protein/lipid polymer structure. This hard and lipophilic layer of the epidermis and the surface hairs would not easily retain dirt if it were not for a hydrolipid film that covers the outermost layer of skin and that picks up particles of soil. This natural outer film of lipid entraps and glues environmental dust, pollutants, smoke, keratinous debris, organic and inorganic compounds in sweat, cosmetics, and other substances that come in contact with it. The hair of the scalp (corresponding to a surface area of about 8 square meters, or 86 square feet, for an average female head) is cleansed regularly. The scalp gets coated with sebum, the product of the sebaceous appendages that flows into hair follicles and a natural lubricating oil that contributes luster to the hair, on the one hand, but entraps dirt, on the other.
Washing the skin consists of the removal of the outer layer of grease (lipid) in which the soil (no matter what kind) is embedded. It is a complex physicochemical process that includes the following:
1.A weakening of the binding forces between the keratinized epithelium and the layer of grease via the reduction of the surface tension between the water and the water-resistant oil/grease. Because of this reduced surface tension, water (and surfactant molecules) can penetrate into the finest wrinkles of the skin. In this way, more and more interface is occupied by surfactant, and the adhesiveness of the soil-containing layer is further weakened, a process facilitated by mechanical rubbing.
2.Transfer of portions of the layer of oil to the aqueous vehicle. It is facilitated by the action of the micelles created when the soil was emulsified. The micelles have negatively charged surfaces and are repulsed by the overall negative charge of the keratin of the skin epithelium.
3.Dispersion/suspension of the oil and dirt particles in the soap foam, preventing these particles from being redeposited on the surface.
Washing the skin consists of the removal of the outer layer of grease (lipid) in which the soil (no matter what kind) is embedded. It is a complex physicochemical process that includes the following:
1.A weakening of the binding forces between the keratinized epithelium and the layer of grease via the reduction of the surface tension between the water and the water-resistant oil/grease. Because of this reduced surface tension, water (and surfactant molecules) can penetrate into the finest wrinkles of the skin. In this way, more and more interface is occupied by surfactant, and the adhesiveness of the soil-containing layer is further weakened, a process facilitated by mechanical rubbing.
2.Transfer of portions of the layer of oil to the aqueous vehicle. It is facilitated by the action of the micelles created when the soil was emulsified. The micelles have negatively charged surfaces and are repulsed by the overall negative charge of the keratin of the skin epithelium.
3.Dispersion/suspension of the oil and dirt particles in the soap foam, preventing these particles from being redeposited on the surface.