Effect of shampoo, conditioner and permanent waving on the molecular structure of human hair.

Yuchen Zhang,Richard J Alsop,Fei-Chi Yang,Asfia Soomro,Maikel C Rheinstädter

doi:10.7717/peerj.1296

Abstract

The hair is a filamentous biomaterial consisting of the cuticle, the cortex and the medulla, all held together by the cell membrane complex. The cortex mostly consists of helical keratin proteins that spiral together to form coiled-coil dimers, intermediate filaments, micro-fibrils and macro-fibrils. We used X-ray diffraction to study hair structure on the molecular level, at length scales between ∼3–90 Å, in hopes of developing a diagnostic method for diseases affecting hair structure allowing for fast and noninvasive screening. However, such an approach can only be successful if common hair treatments do not affect molecular hair structure. We found that a single use of shampoo and conditioner has no effect on packing of keratin molecules, structure of the intermediate filaments or internal lipid composition of the membrane complex. Permanent waving treatments are known to break and reform disulfide linkages in the hair. Single application of a perming product was found to deeply penetrate the hair and reduce the number of keratin coiled-coils and change the structure of the intermediate filaments. Signals related to the coiled-coil structure of the α-keratin molecules at 5 and 9.5 Å were found to be decreased while a signal associated with the organization of the intermediate filaments at 47 Å was significantly elevated in permed hair. Both these observations are related to breaking of the bonds between two coiled-coil keratin dimers.

Highlights

The human hair has a complex internal structure consisting of many layers including, from outside in, the cuticle, the cortex and the medulla, all bound by the cell membrane complex
X-ray diffraction is able to visualize signals corresponding to keratin coiled-coils, intermediate filaments and lipids in the cell membrane complex
The hair structure of a single individual under shampoo, conditioning and permanent waving treatments was studied in the natural state using wide angle and small angle X-ray diffraction

Summary

Introduction

The human hair has a complex internal structure consisting of many layers including, from outside in, the cuticle, the cortex and the medulla, all bound by the cell membrane complex. The medulla is a loosely packed, disordered region at the centre of the hair shaft. It is surrounded by the cortex, the structure that makes up majority of the hair fibre and contains keratin proteins and structural lipids. The cuticle is a layer of overlapping dead cells that form a protective barrier against the outside environment (Robbins, 2012)

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