Hair science holds a great impact on society in the cosmetics industry and in biomedicine. Over the last few decades, there has been a significant societal paradigm shift for people with curly hair to accept the natural morphological structure of their curls and style their hair according to the innate, distinct, and unique material properties that their curly hair possesses. These societal and cultural shifts have given rise the development of new hair typing systems, beyond the traditional and highly limited ethnicity-based distinction between Caucasian, Mongolian, and African types. L’Oréal developed a hair typing taxonomy based on quantitative geometric features among the four key curl patterns – straight, wavy, curly, and coily, however the system fails to address the complex diversity of curly and coily hair. Andre Walker’s classification system is the existing gold standard for classifying curly hair types, however the system relies upon qualitative measures to classify hair type, which makes the system vague and ambiguous to the full diversity of phenotypic differences. The goal of this research is to use quantitative methods to identify new geometric parameters to better classify curly and coily hair and therefore provide more information on the kinds of personal care products that will resonate best with these curl patterns. The motivation behind employing hair typing is to better categorize hair phenotype and target appropriate personal care products tailored for specific hair phenotypes to maximize the desired appearance and overall hair health. This was accomplished by distinguishing new mechanical and physical properties of several types of human hair samples. Mechanical properties were measured under tensile extension using a texture analyzer (TA) and a dynamic mechanical analyzer (DMA). Both instruments measure force as a function of applied displacement, thus allowing the relationship between stress and applied stretch ratio to be measured as a hair strand uncurls and stretches to the point of fracture. Morphological properties were measured using scanning electron microscopy (SEM), photogrammetry, and optical microscopy. From the resulting data, correlations were made between fiber structure and mechanical performance. This data will be used to draw more conclusions on the contribution that morphology has on hair fiber mechanics and will promote cultural inclusion among researchers possessing curly and coily hair.

Reimagining hair science: A new approach to classify curly hair phenotypes via new quantitative geometrical & structural mechanical parameters

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