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Left: Cross-sections observed by optical microscopy for Caucasian hair selected to analyze by μ-FTIR, regions were manually determined. Right: Chemical map of second derivative obtained at 2850 cm−1 (CH2 symmetric stretching) of Caucasian virgin hair (a) and Caucasian delipidized hair (b).
Cerdanyola del Vallès, 14th December 2021 Researchers from the Institute for Advanced Chemistry of Catalonia (IQAC-CSIC) in collaboration with the ALBA Synchrotron have studied and compared the lipid distribution of African, Caucasian and Asian hair fibers. More specifically, the work has determined the presence, distribution, and function of lipids of each ethnicity. The differences observed can explain some of the barrier properties against external substances that each hair type presents. In particular, African hair was demonstrated to have more lipids that are highly disordered, which can explain its differentiation from Asian and Caucasian hair concerning moisturization and swelling (when water content inside the fiber increases).
There are very few studies on hair morphology across populations and usually are focused on the protein within the hair fibers, but results show just slight differences between ethnicities, which cannot explain the physical differences. However, some studies have found that lipids play a key role in maintaining adequate water permeability and the hydrophobic (or “waterproof”) character of the hair fiber surface.
Researchers observed differences in the lipid fraction on the three ethnic hair types. The African hair structure showed the greatest lipid content in all of the hair regions: the medulla, which is the center-most portion of the hair. The cortex, which makes up the bulk of the hair and determines its strength and color. And the cuticle, which is the outermost layer of the hair, is composed of overlapping cells with a scale-like appearance and protects the cortex. The Asian hair had the lowest amount of lipids, and Caucasian hair has a similar lipid order in all regions, which is higher than that of cuticles of Asian and African types, in accordance with previous studies.
The results from this work can have particular relevance to chemists and new-product development specialists who work in the ethnic hair-care market.
Experiments at the MIRAS beamline in ALBA
Fourier Transform Infrared (FTIR) microscopy experiments were carried out at the MIRAS beamline in the ALBA Synchrotron to study the lipid fraction distribution in the different types of hair. The high brightness of synchrotron light plays an important role in studying localized biochemical phenomena in living single cells.
The study of the lipid peaks observed in the synchrotron-based infrared spectra enabled the determination of the lipid distribution and order on the different hair regions.
"With the synchrotron light techniques that we have used, we could see where the lipids location in the hair is and how it is structured", explained Luisa Coderch, main author of the paper and researcher in IQAC-CSIC. "The hair has more lipid in the innermost part and less in outer part. African hair has more lipids and they are disordered, which means that it is more permeable to dye the hair or hair treatments, unlike the Asian hair", concluded Coderch.
Reference: Clara Barba, Marc Adrià Oliver, Meritxell Martí, Martin Kreuzer, Luisa Coderch. Lipid distribution on ethnic hairs by Fourier transform infrared synchrotron spectroscopy. Skin Research and Technology 2021. DOI:10.1111/srt.13093
With the collaboration of Fundación Española para la Ciencia y la Tecnología. The ALBA Synchrotron is part of the of the Unidades de Cultura Científica y de la Innovación (UCC+i) of the FECYT and has received support through the FCT-20-15798 project.
