Hair lipids composition

Wertz, P. and Norlen, L., Confidence intervals for the true lipid composition of the human skin barrier in Skin, Hair, and Nails. Forslind, B. and Lindberg, M., Eds., Marcel Dekker Inc., New York, Basel, 2004, p. 85. 

At the other end of the spectrum, combined X-ray (fluorescence, absorption and diffraction) and IR microscopic analyses on the same sample represent an activity of growing interest among the biomedical community. For example, protein mis-folding has been correlated with trace metal uptake in Alzheimer s disease [32], Parkinson s disease [91], scrapie [36] and amyotrophic lateral sclerosis [91], Likewise, in human hair the protein and lipid composition of the cuticle, cortex and medulla have been correlated with trace metal content associated with mummification techniques [74], and with environmental metal exposure [92]. 

Deficiencies in both n-3 and n-6 FFA are seen clinically and can be differentiated by predominant symptoms. Common symptoms of n-6 FA deficiency include growth retardation, skin lesions, impairment of reproduction, loss of hair, fatty liver, and disorder in the water balance. In contrast, n-3 FA deficiency spares growth and reproduction, but is associated with reduced learning, impaired vision, and polydipsia. Abnormal n-6-to-n-3 ratios have been linked to changes in the vascular membrane lipid composition and the increased incidence of atherosclerosis and inflammatory disorders. In humans, EFA deficiencies have been observed in babies however, EFA deficiency in adults was unknown until parenteral feeding with a formula diet was administered over a long period of time. 

Leeder and Rippon [85] have analyzed the lipid composition of wool fibers after removing surface grease. Continued extraction with solvent removed the beta layers evidenced by electron microscopy however, the extract contained free cholesterol and free fatty acid and triglycerides but negligible quantities of phospholipid normally associated with biological membrane lipids. Koch [86], in his work with internal lipid of human hair, did not report significant quantities of phospholipid. These lipid-protein layers of hair are most likely related structurally to those of the epicuticle. 

Composition of Human Hair Lipid 93 Table 2-13. Composition of FFA in human hair lipid. 

It was indicated previously that the amount of sebaceous secretion changes with age near puberty. The composition of the sebaceous secretion also changes with age near puberty. Nicolaides and Rothman [146] have shown that the paraffinic hydrocarbon content of sebum is highest in children (boys), lower in men, and lowest in women. These same two scientists have also shown that the squalene content of the hair lipid of children, at approximately 1.35% of the total lipid content is about one-fourth that of adults (sebum from boys age 6 to 12 was examined in this study and compared to that from both men and women). In addition, the cholesterol content of the hair lipid of children is less than that from adults 3.7% versus 12.2% [146]. 

This test result suggests that the amount of internal lipid in dry and oily hair are virtually identical. Therefore, the primary differences between dry and oily hair lipid are in the amount and the composition of the surface... 

Converse flexoelectric studies of lyotropic liquid crystals, such as vesicles, is still an active subject. Notably, the sensory mechanism of outer hair cell composite membranes " can be understood by the flexoelectric properties of the lipid bilayer. The converse of this effect, i.e., a voltage-generated curvature, has also been observed and was discussed by Todorov et Another related phenomenon is the ferroelectricity which results from the tilted layered structures of chiral molecules, which has been discussed extensively since the 1980s.Ferroelectric phases are called... 

Analysis of hair lipid reveals that they are very complex, consisting of saturated and unsaturated, straight and branched fatty acids with chain lengths of from 5 to 22 carbon atoms. The difference in composition of lipids between persons with dry and oily hair is only qualitative. Fine straight hair is more prone to oiliness than curly coarse hair. 

Lipid extracted from human hair is similar in composition to scalp lipid [134]. Thus, the bulk of the extractable lipid in hair is free lipid however, cell membrane complex lipid is also partially removed by extraction of hair with lipid solvents or surfactants. In a sense, the scalp serves as a lipid supply system for the hair, with sebum being produced continuously by the sebaceous glands [135]. Sebum production is controlled hormonally by androgens that increase cell proliferation in the sebaceous glands, and this in turn increases sebum production [135,136], although seasonal and even daily variations in the rate of sebum production do occur [137]. 

Several studies have shown significant differences in the composition of oily versus dry hair. Perhaps the most comprehensive study in this regard was by Koch et al. [152], who examined hair surface lipid from 20 dry- and oily-haired subjects, three days after shampooing, and found the following correlations with increasing hair oiliness ... 

Creme rinses and most hair conditioners are basically compositions containing cationic surfactant in combination with long chain fatty alcohol or other lipid components. Distearyldimonium chloride, cetrimonium chloride, stearalkonium chloride, and behentrimonium methosulfate are typical cationic surfactants used in many of today s hair conditioning products. Amines like dimethyl stearamine or stearamidopropyl dimethylamine are other functional cationics used in these products. Cationic polymers such as Polyquaternium-10 (quaternized ceUulosic) and Polyquatemium-7 (copolymer of diallyl dimethyl ammonium chloride and acrylamide) are also used (more in shampoos than in hair conditioners) however, care must be taken to avoid buildup on hair when formulating with cationic polymers. See the section on Cationic Polymers and Their Interactions with Hair in Chapter 7. 

Lipid soils are the primary hair soil and are principally sebaceous matter. For a more complete description of the chemical composition of sebaceous soil, see Chapter 2. 

Koch et al. [9] report that repeated shampooing removes 70 to 90% of the ether-extactable hpid and that enzymatic hydrolysis of hair after ether extraction, followed by extraction of the residual membranes, yields internal lipid. Koch found the composition of this internal lipid to be somewhat similar to that of surface hair hpid. Koch, therefore, concludes that internal lipid of hair must in part originate from the sebaceous glands (see the section entitled Intercellular Matter and the Non-Keratin Regions of Hair of Chapter 1). 

The composition of the lipid itself may influence its transport because ingredients that either lower the surface tension of the sebum or increase its fluid nature (make it less viscous) can facilitate transport and even increase the perception of oiliness. In addition, other ingredients left behind on the hair surface (e.g., conditioning agents) may exacerbate oiliness in an analogous manner. 

Leeder [16] has shown that the composition of the cell membrane complex (see Section 5.2.5), of which the lipid fraction is one component, has a dramatic influence on fiber and fabric properties. The composition of the internal lipid fractions of a number of specialty animal fibers has been the subject of detailed study [309,310]. Wool, cashmere, cashgora, and mohair contain free cholesterol and desmosterol in the ratio of 1.7-2.6 1 [309]. By comparison, llama, camel, and alpaca fibers contain virtually no free cholesterol or desmosterol. The results for yak vary widely [309,310]. Rabbit and dog hairs have distinctive sterol compositions, which are unlike each other and different from that of wool and goat fibers. 

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