Type 4 hair, or very curly hair, experience more long tear fractures than other hair types due to repeated stretching, unwisting and buckling of the hair strand, according to new research published in the International Journal of Cosmetic Science. The research was performed by TRI Princeton, a nonprofit scientific research and education institute in Princeton, New Jersey.
The study was performed in two locations: New Jersey, United States and Cape Town, South Africa. Subjects aged 18 to 55 with varying hair types without chemical treatment were invited to participate. Researchers performed fatigue tests and light microscopy to assess the fracture patterns on the hair.
According to the results of the study, male/female breaks and tear fractures predominated across all hair types. Hair Type 4 displayed significantly more tear fractures and fewer male-female breaks than Types 2 and 3, and Type 4 had significantly more split fractures.
The researchers believe that the differences in fracture patterns are due to the difference in torsional stresses on the hair fiber. Previous research has suggested that stretching a coily hair fiber is similar to a spring-like helix, creating stress points along the fiber.
“In conclusion, these data suggest that repeated stretching, unwisting and buckling of very curly, Type 4 hair in fatigue experiments more frequently creates longitudinal cracks,” the authors said. “In contrast, the repeated stretching of straighter hair (Types 2 and 3) typically creates cuticle cracks perpendicular to the fiber axis, which eventually develop into male/female fractures.”
The authors state that further work is needed to determine how the fracture patterns relate to those caused by routine combing damage, as well as the exact location of failure points along the hair fiber.
