Human hair has been extensively studied for decades, but until now, a complete understanding of its structure had proven elusive.
"Hair traditionally has been constituted of three regions: medulla (central part of the hair), cortex (biggest volume fraction of the hair) and the cuticle (external part of the hair)," project leader Vesna Stanic, a scientist working at the Brazilian Synchrotron Light Source, told Discovery News.
"We discovered a new intermediate zone, which is in between the cuticle and cortex," she added.
Stanic and her team made the discovery by combining an ultra powerful submicron X-ray beam with cross-sectional geometry. The original goal was to just study materials used in hair treatments, and how they affect hair. While doing this, Stanic wondered about the diffraction patterns of hair.
Diffraction is the bending of waves around obstacles and openings. X-ray diffraction patterns of a given material can therefore reveal the local arrangement of both molecular and atomic structures.
Diffraction patterns of human hair have been documented before, but they usually involved pointing the X-ray beam perpendicular to the hair fiber axis. Stanic and her team decided to do something different.
"We performed a full diffraction map from a 30-micron-thick cross section of hair, with an incident beam parallel to the hair axis, and then compared it to the diffraction map with the beam perpendicular to the hair axis," she explained.
Before this study, human hair was thought to be composed only of a fibrous protein called alpha keratin, as well as certain minerals and lipids. The scientists were therefore extremely surprised to find that a key diffraction feature of alpha keratin was absent in the area between a hair strand's cuticle and cortex. The pattern instead corresponded to beta keratin.
Previously, beta-keratin was associated with reptiles and birds. It is what makes claws, scales, beaks and feathers strong, tough and, in the case of feathers, also flexible and elastic.
Alpha and beta keratin are similar molecules, but they have very different sizes and shapes.
Stanic explained, "The basic difference between alpha and beta keratin is the molecule conformations. We can say that beta keratin is essentially stretched alpha keratin. Alpha keratin has a helical structure, while beta is typically arranged in sheets."
The discovery comes on the heels of other research helping to explain why humans from different parts of the world have distinctive hair types. The reason can be summed up in one word: Neanderthals.
Daven Presgraves, an associate professor in the Department of Biology at the University of Rochester, told Discovery News that people of non-African heritage today retain Neanderthal alleles (alternative gene types) at genes affecting keratin filaments.
"The implication is that these Neanderthal-derived alleles were particularly well adapted to Eurasian environments in which they'd evolved for several hundred thousands of years," Presgraves told Discovery News. "Modern humans who interbred with Neanderthals on their way out of Africa were, in effect, able to borrow these keratin-associated alleles, perhaps accelerating adaptation to a Eurasian environment that was new to them."
Read more at Discovery News
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