Ethnic hair: Thermoanalytical and spectroscopic differences

Abstract

Hair is a protein fibre (85%) and contains low levels of lipids (1%-5%) and water (10%). Hair consists of a follicle and a shaft. 1 The shaft, the part of the hair that is visible above the skin, has a width of 50-100 μm and is composed of three main parts: the medulla, the cortex and the cuticle. The medulla, which possesses a diameter of 5-10 μm, is composed of loosely packed cells and is not always presented in the hair. The cortex, which is 45-90 μm thick, accounts for 90% of the total hair mass. Seven to ten tetramer spiral units, known as intermediate filaments, compose the microfibrils of the cortex. The intermediate filaments are surrounded by a matrix of high-glycine/tyrosine proteins. The proteins interact with the intermediate filaments through intermolecular disulphide bonds that provide inertness, rigidity and high mechanical strength to the hair fibres. 1,2 The cuticle, at the surface of the hair, has a 5-µm-thick protective covering consisting of superimposed layers of flat overlapping structures. 3,4 Low levels of lipids form part of the intercellular membrane complex, and these lipids are presented in the cortex and in the cuticle. In addition, the hair medulla also contains a fraction of rich lipids. 5,6 The presence of cuticles is fundamental to maintain the internal water content of the

How different is human hair? A critical appraisal of the reported differences in global hair fibre characteristics and properties towards defining a more relevant framework for hair type classification

“…Internal lipids in the fibre originate from the follicle [56] and African hair was reported to have higher internal lipids than Asian and Caucasian hair, and a higher content of cholesterol ester and cholesterol sulphate along with the lower concentration of ceramides [57, 58]. Another study of cuticle lipids also places African hair as presenting the highest amount [59]. Caucasian grey hair was reported to have less lipids in the cuticle than brown hair [60], but no other investigations of the effect of greying were found.…”

“…Dynamic vapour sorption (DVS) comparisons report the highest amount of water in the Caucasian, followed by African, and the lowest in the Asian hair, inferring that Asian hair is more resistant to hydration changes. On the other hand, African hair had the highest diffusion coefficient, and Caucasian the lowest, thus implying that water content per se is not related to diffusion capacity [59]. Wet Caucasian hair was also reported to have higher radial swelling than the other hair types [7].…”

A systematic review on the lipid composition of human hair

“…Caucasian fibers with their highly ordered lipids are more resistant to moisture uptake and are also the most hydrated. 23,24 Comparatively, African hair has the lowest lipidic order and highest water diffusion rate, despite high cuticle lipid content. 24 Other studies found that hair fiber permeability and humidity resistance is not affected by lipid removal.…”

“…23,24 Comparatively, African hair has the lowest lipidic order and highest water diffusion rate, despite high cuticle lipid content. 24 Other studies found that hair fiber permeability and humidity resistance is not affected by lipid removal. 2,25 Gray hair fibers with their decreased unsaturated lipid content have a lower capacity to absorb water contributing to their clinical "stiffness" as compared to pigmented hair fibers.…”

The Role of Lipids in the Process of Hair Ageing

“…The µ-FTIR was performed with a MIRAS beamline at the ALBA Synchrotron 35 using a Hyperion 3000 Microscope (Bruker) equipped with a 36× magnification objective and condenser coupled to a Vertex 70 spectrometer (Bruker) with a 50 µm HgCdTe (MCT) detector that was continuously purged with N2 gas, as described elsewhere [11,32,33]. Hair tufts (1 cm) were embedded into an optimal cutting temperature (OCT) compound (Bright Instruments) and immediately frozen using liquid N2.…”