Effects of Silicone Oil Viscosity on the Physical Structure and Damage Mechanisms of Hair during Permanent Wave Treatment

This study investigated the effects of varying silicone oil viscosity on the physical structure and damage mechanisms of hair during permanent wave treatment of untreated hair (N), permanent wavy hair (P), and dyed hair (C). Hair treatments were formulated using dimethicone with viscosities of 6 cSt, 1,000 cSt, and 10,000 cSt. Wave efficiency, hair thickness, and tensile force were then evaluated. Hair cuticle, cross-sectional structure, and cuticle thickness were observed using FE-SEM, and elemental composition was analyzed using EDS. The results showed that wave efficiency was highest for untreated hair at VL_N, for permanent wavy hair at VM_P, and for dyed hair at VH_C. No significant differences were observed in hair thickness across all hair groups. Hair tensile force, cuticle thickness observed using FE-SEM, and sulfur (S) content analyzed using EDS — an important indicator of hair damage — all exhibited the highest values for VH in N, P, and C showing a consistent pattern. These findings indicate that wave curling performance and hair damage are significantly influenced by the silicone oil viscosity in hair treatments. This study provides fundamental and valuable data for determining the optimal silicone viscosity for hair treatments and may be expected to significantly contribute to the development of hair cosmetic products utilizing the benefits of silicone.