The proper hair care for curly or kinky locks can be incredibly confusing, and while there are more brands out there focusing on different textures of hair, the vast majority of hair studies have been conducted on straight or wavy hair strands for Asian or white hair. Advice for maintaining your mane can even be contradictory and leaves highly variable results.
A group of scientists are working to bring some order to this chaos by identifying hair properties, like the number of curls or coils in a given length of hair, that could eventually help consumers select products and get consistent results. The findings are being presented at the American Chemical Society’s spring meeting.
“As an African American, I was born with very curly, seemingly unmanageable hair, and other ethnicities can possess similar hair properties,” Spelman University chemist Michelle Gaines, this project’s principal investigator, said in a statement.
When Gaines became pregnant, she stopped using chemical relaxers to straighten her hair and saw an overwhelming variety of products available to care and style for natural hair. It didn’t help Gaines that there was limited guidance about the best options for her specific hair type, followed by conflicting advice on social media and from friends.
“As a polymer chemist and materials scientist, I thought it would be great to start a project where I could study the nuances of my hair, because I felt like it wasn’t very well understood,” Gaines said.
With a team of undergraduates and collaborators at Spelman University and the University of Massachusetts Amherst, Gaines wanted to see if she could identify differences in properties beyond curl shape and tightness, and use those differences to develop a classification system that is more precise and quantitative.
The team looked at wavy, curly, and kinky hairs and measured their mechanical properties with a texture analyzer. When a strand of hair is uncurled and stretched until it breaks, texture analyzers measure stress, force, and other parameters.
Among their findings, the team found a newly developed parameter called a “stretch ratio.” This ratio quantifies and compares the force that is needed to uncurl a strand of hair until it straightens. The ratio was negligible for straight hair, about 0.8 for wavy, 1.1 for kinky, and 1.4 for curly. The team believes that this measurement could be a quantifiable way of distinguishing between hair types since it indicates the initial curliness of hair.
The team also measured geometric properties including diameter, cross section, and the 3D shape of hair strands. This helped them develop new parameters, including the number of complete waves, curls, or coils—known as contours—that were measured on three centimeter lengths of hair. According to the results, wavy hair had less than one full contour in that length, curly hair had about two, and kinky or coily hair had approximately three or more. These results could help people classify their own hair by counting contours.
Cuticle layers that protect the hair surface are smoother, larger and further apart (left) in wavy hair than in curlier hair (right). CREDIT: Michelle Gaines.
Gaines has also started to examine the layer that protects the surface of each hair fiber, or the cuticle. This layer consists of flat cells that overlap each other, like roof shingles, and have a natural tendency to open and close reversibly when exposed to plain water, shampoos, and conditioners. Retaining excessive acid and moisture permanently damage the cuticles and make the strand more porous and retain more moisture. Preliminary findings show that wavy hair has cuticle layers that are larger and spaced further apart compared to curly or coily hair. The cuticle edges are smoother in wavy hair, and these findings could help scientists explain why coily and curly tresses dry out quicker than wavy or straight locks.
As a whole, Gaines hopes, this work will identify the best parameters for better hair product development so that consumers can buy the best products for their specific hair needs.
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