Mechanical hair removal

Hair Removers. Hair removers are designed to remove hair from the skin surface without cutting ia order to avoid uadesirable stubble. Cosmetic products have beea developed for chemical destmctioa of hair, that is, depilatioa, and for facilitating mechanical hair removal, that is, epilation. 

The differences in the amino acid chemistry of the hide coUagen and the hair keratin are the basis of the lime-sulfide unhairing system. Hair contains the amino acid cystine. This sulfur-containing amino acid cross-links the polypeptide chains of mature hair proteins. In modem production of bovine leathers the quantity of sulfide, as Na2S or NaSH, is normally 2—4% based on the weight of the hides. The lime is essentially an unhmited supply of alkah buffered to pH 12—12.5. The sulfide breaks the polypeptide S—S cross-links by reduction. Unhairing without sulfide may take several days or weeks. The keratin can be easily hydrolyzed once there is a breakdown in the hair fiber stmcture and the hair can be removed mechanically. The coUagen hydrolysis is not affected by the presence of the sulfides (1—4,7). 

The hair of the back of the head was mechanically removed from an area of 3 x 4 cm under ether anaesthesia. The skin was dissected to the fascia. After the operation the wound was daily treated with a 5% ointment consisting of the appropriate silatrane and a vaseline-lanolin base until complete microscopic healing. The wounds of the control animals were covered only with the vaseline-lanolin mixture. The other control group was not treated at all. The wounds were examined daily and measured until complete healing. Then the animals were killed. From the wound area a piece of skin was taken for a histological analysis. 

Other studies unfortunately dealing only with the time necessary for the cut hair to grow were carried out on female white rats and guinea pigs of the same age70. After having the hair mechanically removed the animals were fed on the diet containing 10 mg/kg of the examined preparation. 

The principles outlined in Section 3.6.6 apply to both the removal and anti-redeposi-tion of soils, and to detergency in both industrial and personal care situations. There are, however, some differences between the application of detergency in an industrial setting (Section 12.2.1) and in a household setting. For example, whereas industrial cleaning usually involves hard surfaces that cannot mechanically hold soil, fabrics can hold soil mechanically, even after the soil has been removed from the fibre surfaces. In addition, fabrics can usually swell in aqueous solution, are permeable to small molecules, and may contain charged or polar surface groups that can interact with soil. An effective shampoo or skin cleaner needs to displace dirt and keep it dispersed so it does not redeposit before the hair or skin can be rinsed. 

Historically, ideas of casein micelle structure and stability have evolved in tandem. In the earlier literature, discussions of micellar stability drew on the classical ideas of the stability of hydrophobic colloids. More recently, the hairy micelle model has focused attention more on the hydrophilic nature of the micelle and steric stabilization mechanisms. According to the hairy micelle model, the C-terminal macropeptides of some of the K-casein project from the surface of the micelle to form a hydrophilic and negatively charged diffuse outer layer, which causes the micelles to repel one another on close approach. Aggregation of micelles can only occur when the hairs are removed enzymatically, e.g., by chymosin (EC 3.4.23.4) in the renneting of milk, or when the micelle structure is so disrupted that the hairy layer is destroyed, e.g., by heating or acidification, or when the dispersion medium becomes a poor solvent for the hairs, e.g., by addition of ethanol. 

Drugs placed on the surface of hair must have some mechanism for entry into the hair matrix. If a solid is placed on the hair surface, most of it can be readily removed. However, after the deposition of the solid drugs onto the hair surface, hair may be bathed at some point in an aqueous media, be that sweat, sebum, normal hygienic solutions, or during the hair analysis procedure. Alternatively, an individual might come in contact with a solution of a drug by transfer of sweat from another individual. It is for these reasons that we and others studied solution phase transfer as the vector for admission and incorporation of drugs into hair. 

Various mechanisms are involved in removing the oily materials. These include roll-up, emulsification, liquid crystal formation, and solubilization. In the following sections the mechanisms and their relative importance in the hair cleaning process are discussed. 

More work is needed to determine the exact contribution of solubilization to the cleaning of different soils. However, solubilization is undoubtedly a highly significant cleaning mechanism and, quite likely, is the most important means by which shampoos remove soils from human hair. 

An examination of the composition and physical state of sebum suggests that several cleaning mechanisms can operate during its removal from hair. Since sebum is completely molten at body temperature [122], it can be effectively removed by the roll-back mechanism. Also, the presence of approximately 25% free fatty acids in sebum indicates, as discussed in Section IV.C.3, that it is subject to removal by emulsification and mesophase formation. Finally, because the concentration of detergents during shampooing is well above their critical micelle concentrations, sebum can also be cleaned from hair by solubilization. 

Solubilization by anionic surfactants is another possible mechanism for cleaning quats. However, Reich and co-workers [157,158] found that solubilization of CTAC and SAC by lauryl and laureth sulfates (1 to 5 EO) was ineffective owing to formation of surfactant-quat complexes that were insoluble in ALS or SLES and, thus, difficult to remove from hair. In this case, reducing the carbon chain length of the quat to 12 or the chain length on the anionic surfactant to 10 resulted in more soluble complexes and more effective removal of the cationic soil. 

---