A wide range of hair shape and color variations exists. Although differences in human scalp hair shape are visually apparent, the underpinning molecular insights are yet to be fully explored. Researchers at Nexxus report on the determination of differences at the protein level between two distinct groups of hair shape: very straight samples versus very curly hair samples. 
 
The research was published in the May/June issue of the Journal of Cosmetic Science. Nexxus scientists at Unilever created Nexxus Curl Define, which launched this past January 2021 as a scientifically customized range for curls.
 
According to Unilever, until now, no one has gone as deep as Nexxus protein researchers to understand curls at the molecular level. Following a decade-long research program, Nexxus uncovered that curly and straight hairs don’t just have a different structure, but the proteins that make up those structures are actually different. 
 
Findings showed there are certain proteins that appear with two to six times greater frequency in curly hair than in straight (specifically, curly hair proteins are much richer in specific building blocks it needs—glycine and serine amino acids—than other proteins). 
 
Knowing curly hair is innately prone to breakage, Nexxus used this proteomic insight to create Curl Define, a four-product range designed to strengthen and moisturize curls and coils from 3A up to 4C. Silk protein was infused into the Curl Define blend, as it is inherently rich in the protein building blocks of glycine and serine. Nexxus researchers also infused marula oil, as it is known for nourishment. 
 
In this study published in the Journal of Cosmetic Science, proteomic technologies were applied to determine whether differences in protein abundance could be observed between the very straight hair samples and the very curly hair samples. Overall, 362 proteins were identified across all samples, with 217 confident protein identifications that were detected and quantified in at least 75% of all samples. To ensure rigorous statistical analysis, further analysis was only based on the 217 proteins that were detected and quantified in most samples. 

According to Nexxus researchers, differences in structural proteins are likely to inform about potential differences in hair performance and those associated with insults and interventions. When looking at the top 20 proteins contributing to the discrimination of the curly versus straight hair shape in the first component, most can be linked to structural protein components of hair; that is, keratin or KAP families, with keratin K85, the strongest contributor to the distinction of the very straight hair shaft pools, whereas KAP 13-2 has the most discrimination power in the very curly hair pooled samples. Although no direct link has been reported in the literature, another protein from the KAP13 family, KAP13-1, is present in significantly higher amounts in curly sheep wool fibers than in the same-diameter straight fibers.

K34 and K81 are cortical proteins that have previously been observed to be uniformly distributed across the follicle in both human straight hair and sheep wool. K40 is notably one of the last keratins to be expressed during the hair formation process and is found only in the cuticle of beard and scalp hair.

Nexxus researchers concluded that this proteome analysis between two extreme groups of hair shape indicates that differences at the protein abundance level can provide useful insights into the physiochemistry underpinning differences in hair shape and the relevant hair growth processes which should inform technological interventions for hair care. The researchers noted that although differences between the very curly and the very straight hair sample groups could be identified, the linkage between biogeographic genetic differences and curl phenotype remains unknown and requires further controlled investigation.