Effects of curl type on hair fracture patterns in non‐chemically treated hair

Background The problem of high breakage in textured hair has been investigated by analysing the fracture patterns on hairs broken during fatigue testing. Methods Female panellists, aged 18–55, were recruited in New Jersey, in the United States and in Cape Town, South Africa. None had chemically treated their hair for at least 6 months. Panellists were split into three groups based on their natural curl type: wavy (Walker Type 2), curly (Walker Type 3) or coily (Walker Type 4). Single fibre fatigue testing was performed on a Diastron CYC801 (Dia‐stron Ltd., Andover, UK) fitted with four individual test cells. The instrument was housed in a bench‐top environmental chamber to regulate the humidity. Optical microscopy was used to analyse the fracture patterns in the hair from 16 US panellists and 16 South African panellists. Samples were analysed across Walker Types 2, 3 and 4. The main break patterns were put into seven categories. Results The results show that male/female breaks and tear fractures predominate across all hair types. The incidence of smooth/clean breaks was very low. Data also show that Hair Type 4 has significantly more tear fractures and fewer male/female breaks than Hair Types 2 and 3 ( p < 0.05, Tukey multiple comparison test). Hair Type 4 also has significantly more split fractures, although this was not a commonly seen fracture type. Conclusions These data suggest that repeated stretching and untwisting of very curly, Type 4, hair in fatigue experiments often creates longitudinal cracks. Cracks that then usually progress to form long tear fractures. In contrast, the repeated stretching of straighter hair (Types 2 and 3) normally creates cuticle cracks perpendicular to the fibre axis, which eventually develop into male/female fractures.