Thermal treatments for hair styling are becoming increasingly popular with consumers both at home and in hair salons. The aim of the present study was to reports an investigation into the effects of this treatment by flat iron on Tunisian hairs. Untreated hair (not chemically treated) was obtained from a volunteer woman who have 34 years old. Individual hair fibers were mounted in parallel arrangement and subjected to 20, 40, 60 and 80 cycles of curling with the flat iron. Each cycle consisted of fifteen seconds of heating at a temperature of 180°C and fifteen second of cooling. In the other hand, the same hair fibers were bleached using H2O2 and subject to the same thermal treatment as virgin hair. The resulting damage to the fibers has been investigated and quantified by tensile measurement and surface characterization. Tensile properties were performed using a Miniature Tensile Tester Model 675 of Dia-Stron and surface characterization was examined using the SEM. After the cited treatment, the cuticle which is the outer covering surrounding and protecting the cortex was destroyed and a cracking of the cuticule cells and a scale lifting was observed for both virgin and bleached hair. It has also contributed to a progressive decrease in the tensile properties of the hair. The elastic modulus and the break stress have respectively decreased of 12.4 % and 18.18% for virgin hair. However, bleached hair loosed 35.7% and 50% respectively of the elastic modulus and the break stress at 100 % RH. In conclusion, the thermal treatment has conducted to the hair surface modification and cuticle damage. In addition, there was a significant reduction in tensile properties after treatment as a function of exposure time especially bleached hair which was affected by the curling more than virgin hair.
