HAIR CARE
A rough guide to testing hair health
Daniel Brown, Hadya El Shourbagy, Phillip Green, Rachael Tucker - James Robinson Speciality Ingredients
Hair means different things depending on a person’s point of view. To a consumer, hair is an identity and an expression of their personality. Hair tells the story of a consumer’s history and is a marker of ethnicity or culture. For a consumer hair health can affect their lives in very real ways by impacting mood, confidence and self-esteem. From a scientific perspective, a hair fibre
consists of a medulla, cortex and cuticle. For a James Robinson Speciality Ingredients (JRSI) scientist, the parts of the hair of particular interest are the cortex and the cuticle. The cortex is comprised mainly of a protein filament called keratin, which is packed full of disulfide bonds to give it strength. The cuticle is coated in lipids that protect the surface, providing smoothness and shine.
Hair health – How to test what consumers want? A consumer’s perception of healthy hair is hair that is strong, looks great, and is manageable. Consumers want hair with volume, great colour, shine and with soft feel. Consumers want hair that gives them confidence. At JRSI, our role is to take our understanding
of what hair is and apply it to create products that gives the consumer what they want. It is therefore essential for us to quantify the qualities that are important to consumers. Our applications team can do this with a
dedicated laboratory facility in Manchester designed to test hair health. This facility aids the development of new sustainable products and also means we can provide accurate data to customers to support our claims for these products.
Medulla
Hair structure Hair is designed to be strong, hardwearing and resistant to the elements. The bulk of the hair is made up of the cortex. Cortex cells consist of microfibrils that give hair its flexibility. The microfibrils are surrounded by a protein matrix that is rich in cysteine amino acids, which are the building blocks of proteins. Cysteine forms covalent disulfide bonds and it is these bonds within the cortex that give hair its characteristic strength. Surrounding the cortex is an outer layer of
hair called the cuticle. The cuticle layer is very thin, only about 10 cells deep, but the protein within the cells contains very high levels of the cysteine that again forms strong covalent interactions. As a result, the cuticle is hard and tough,
Cuticle Cortex
Figure 1: Hair shaft under microscope showing cuticle structure and damaged cuticle
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and can even leave an indent in stainless steel. The exterior of the cuticle cells is covered in a hydrophobic layer of lipids and the cells are bound together by the cuticle cell membrane complex (CMC) which, when intact, acts to provide an impervious barrier to damaging molecules and protect the cortex underneath.
Hair strength A consumer’s perception of hair strength is
‘hair that doesn’t break.’ Despite the natural strength and barriers present in hair, modern stresses to which hair is exposed to can cause it to become damaged. Cleaning products can strip away the outer
lipid layer and damage the CMC, allowing water to penetrate, this compromises the integrity of the outer protective layer leaving it susceptible to further damage by abrasion. Damage to the cuticle leads to further harm as modern pollution and cosmetic products can penetrate into the cortex. Of particular harm to hair health are
relaxing and bleaching treatments. Reactive oxygen species (ROS) generated by these treatments penetrate into the cortex of the hair and break apart the covalent bonds between cysteines. Once these bonds are broken the strength of the hair suffers leading to breakages and split ends that a consumer can perceive. Lots of research aims to restore these bonds
and recover hair strength. In an ideal situation, we could repair covalent interactions within the hair, in practice this is unrealistic as once the bonds are broken by ROS they are capped by subsequent reactions meaning they can not simply be reformed. What is possible however is to use products to substitute broken covalent bonds for new linker molecules, which can form ionic or hydrophobic interactions and restore hair strength.
Variables when testing Hair can display vastly different results in strength tests based upon the hair type. For example, Type 1 straight hair generally yields higher tensile strength results compared to Type 4 coily hair, which is more fragile. The hair type and level of damage to the
hair also greatly influences outcomes. In cases of extreme damage, bond-building or hair- strengthening ingredients may not show any positive effects. In addition, environmental factors such as temperature and in particular humidity can affect results. When developing our in-house method for assessing hair strength, we carefully considered all these factors. This includes the selection of hair and its preparation method, such as the level and duration of bleaching, and ensuring that tests are performed under consistent humidity conditions. At JRSI, we can test the strength of the hair with a combination of methods.
January 2025 PERSONAL CARE
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