Curly hair science: Scientists define new ways to measure curly and kinky hair

It may be surprising to know that, as someone who’s been dealing with curly hair for over a quarter of a century now, I still don’t have a solid grasp on exactly which products I should be using on my own.

Minor deviations from the usual hair-care routine can result in almost completely different curl patterns and textures. Not to mention: hair products are sufficiently expensive that I’m hesitant to buy new ones and indulge in a little experimentation.

But new research presented at the spring meeting of the American Chemical Society (ACS), held 26–30 March, might just bring some order to all this curl-related confusion.

Scientists have identified measurable properties – like the number of curls or coils in a given length of hair – that could help us better classify our hair. The research ultimately aims to identify the best parameters for product developers to design, and us curly consumers to select, the most suitable products for the incredibly varied categories of hair.

The research project is led by Dr Michelle Gaines, from the Department of Chemistry and Biochemistry at Spelman College, US, who is inspired by experiences with her own natural hair texture.

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“As an African American, I was born with very curly, seemingly unmanageable hair, and other ethnicities can possess similar hair properties,” says Gaines. “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.”

According to Gaines, there’s a major knowledge gap in previous research into the properties of hair, which she says has been done mostly on wavy or straight strands from white or Asian people.

Gaines set out to try to identify differences in these properties, other than curl shape and tightness, and then use those to develop a precise quantitative classification system for hair.

One of these new parameters is “stretch ratio” – a measure of the force required to uncurl a strand of hair until it’s straight. This is negligible for straight hair, since it can’t be uncurled, but about 0.8 for wavy, 1.1 for kinky and 1.4 for curly hair. 

Another property is the number of complete waves, curls, or coils – known as contours – measured on a three-centimetre length of hair. The team found that wavy hair has less than one full contour in that length, curly has about two, and kinky/coily has approximately three or more.

(Careful investigation of my own hair, using a ruler in the office bathroom, confirms that the curliest pieces sit firmly within that two contours category.)

Gaines has also been examining the layer that protects the surface of each hair fibre – the cuticle –which consists of flat cells that overlap each other, like roof shingles or fish scales.

Cuticles open and close reversibly when exposed to water, shampoo, and conditioner. But hair with cuticles that easily open and close, or have irreversibly lifted due to damage, are more porous and can’t retain moisture as well.

In the latest work, preliminary findings suggest that cuticle layers are larger and spaced further apart in wavy hair than curly hair, and that cuticle edges are smoother in wavy hair. This could help explain why curly and coily hair dries out faster than wavy and straight hair.