Investigating the relationship between the hair fiber proteome and hair quality

Many hair characteristics (e.g. color and curl) are genetically determined. Here, we investigated whether hair quality is also genetically controlled and related to differences in hair composition. Female, Caucasian subjects (n = 292) were recruited into this study and segmented by self-perceived hair quality and by permanent colorant usage. Hair fibers were collected and characterized by amino acid analysis, dry tensile elastic modulus testing and two-dimensional electrophoresis of hair protein extracts. Protein analysis revealed a string of 66 kDa proteins that correlated with hair of high quality. Loss of low molecular weight (14–29 kDa) proteins increased with colorant usage, particularly in hair of low quality. Amino acid analysis showed that the levels of serine and threonine across all the subjects followed bimodal frequency distributions suggestive of a genetic influence. Overall, data suggested that perception of quality was linked to high serine and threonine levels. In addition, where hair was colored, quality was associated with lower cysteic acid levels. Lower cysteic acid levels were not linked to lower colorant usage and our data suggest that high quality hair may be more resistant to colorant damage. Elastic modulus was significantly higher in hair of higher quality (4.65 GPa) compared to all medium and low quality hair combined (4.3 GPa), P < 0.02. This suggests a link between altered hair composition and mechanical properties. In conclusion, the composition and mechanical properties of hair have been linked to hair quality. We hypothesize that hair quality is thus likely to be genetically determined. Understanding of the links between hair composition and its properties could be utilized in the future for designing products targeted to each individual's hair make-up, and for producing diagnostic tools for determining hair quality.