Hair damage from environmental and cosmetic treatments continues to be a concern. Consequently, continuing efforts are under way to understand the mechanisms of hair degradation and to devise means to protect or repair hair from damage. This short review summarizes recent advances in the quest to protect and repair human hair.
It is well-known that hair is comprised of three structural elements: the cortex, which resides in the interior of the fiber; the cuticle, which is wrapped around the exterior; and the medulla, which is a tubular region of low density that resides within the cortex region. It is also well-known that hair can be damaged by exposure to mechanical stress and abrasion from combing and brushing, oxidative stress due to UV irradiation in an oxygen-rich environment, and chemical treatments designed to perm, color, straighten, relax or bleach the hair.
For example, perming causes hair within a molecular weight range of 48 kDa and 60 kDa to lose about 58% of its protein. After such damaging treatments, it is standard protocol to use conditioners to screen the damage by improving wet and dry combing attributes, imparting a soft feel and alleviating static flyaway. However, conventional conditioners do little to restore hair strength.
Synthetic copolymers of styrene and acrylates can be utilized to cover damaged hair and improve shine. One advantage to using polymers as hair fixatives is that they minimize the need for more commonly employed silicones, which can compromise fixative properties. In one case, styrene, butyl acrylate, methacrylic acid and other co-monomers were synthesized via emulsion polymerization and formulated as aerosol hair spray and gel. Shine measurement, film gloss, stiffness analysis, high humidity curl retention and dynamic mechanical analysis were then used to characterize the treated hair. This method does not repair damaged hair, but instead relies on the high refractive index of latex polymers as the means of attaining gloss/luster of the polymer-treated hair.