Integral hair lipid (IHL) is bound to the keratinized cell surface to make an environmentally resistant lipid
envelope. It is mainly positioned on the hair cuticle and inner root sheath. IHL in the hair follicle may
regard as hair barrier to be similar to the epidermal lipid layer functioning as skin barrier. Major
constituents of IHL are fatty acid, phytosphingosine, ceramide in decreasing order. Minor constituents of
IHL are cholesterol, cholesterol sulfate and cholesterol oleate. Cuticle or cortical cell surface in hair are
abundant in fatty acids unlike the keratinized area of epidermis or sebaceous gland, and about 30–40% of
such fatty acids are composed of 18-methyl-eicosanoic acid which is known to be bound to proteins by
ester or thioester bond. Various factors including moisture, solvent, oxidative damage during bleaching
or permanent waving affect IHL. Photochemical changes also can occur in IHL as well as in hair protein
and hair pigment. Lipid metabolism is thought to play an essential role in lipid envelope of hair, but also
involvement in hair development and function.