80 TESTING


protects hair from damage/treats damaged hair, and hair styling/enhancement products used for appearance improvement. Depending on the capacity of entering the


fibre, hair cosmetic products may reach the cuticle surface of the hair fibre or the inner part of the cortex, depending on the size of the presented molecules - smaller molecules can reach the cortex and larger ones act on the cuticle. In order to improve the appearance of hair,


repair hair damages and protect the hair fibres from external damage, products are developed to: ■ Improve combability ■ Seal the cuticles ■ Mimetise the hair natural lipid outer layer: 18- MEA – restore hydrophobicity ■ Enhance shine, smoothness and manageability ■ Avoid or minimize frizz and friction, by neutralising the negative charged net Among the many hair products on the market,


conditioners are often submitted to clinical studies, due to their different actions and usages. The hair shaft has negative electrical charges and conditioning agents have positive charges. Therefore, conditioners act by neutralising


the electrical negative charge of the hair fibre, by attracting positive charges and by greasing the cuticle, with the final result of reduce fibre hydrophilicity. Conditioners also help the raised cuticles to lie down against the hair surface, and, in this way, preserve hair colour and enhance its shyness and smoothness too.7


Testing with human hair tresses Evaluating the efficacy of hair products involves the use of highly accurate equipment. A wide range of instrumental techniques are routinely used in order to claim substantiation. To evaluate structural, chemical, morphological


and physical properties of hair, whether of virgin hair or damaged hair by different agents, and even to evaluate the efficacy of hair care products and to provide support for substantiating hair care claims, several methodologies. Ex vivo tests with human hair tresses have


advantages when compared with in vivo studies as they can provide the necessary data in a shorter period of time, there is no need to select a panel of subjects with specific characteristics and availability to participate in the study, are easier to standardise, and are easier to perform even for high complexity protocols.8 Usually, ex vivo tests are sensitive towards discrimination between products, with both high precision and reliability.9


Some of these ex vivo A


TABLE 1: EX VIVO METHODOLOGIES TO TEST THE EFFECT OF HAIR CARE PRODUCTS AND PROVIDE SUPPORT FOR SUBSTANTIATING HAIR CARE CLAIMS


Claim / Type of evaluation Hair combing/detangling


Antistatic (reduction of flyaway effect)


Anti-frizz/resistance to high rela- tive humidity (RH) conditions


Relaxing/straightening


Silicon deposition by x-ray fluorescence


Split ends Hair breakage


Hair colour fading by consecutive washing procedures


Anti-pollution/pollution particle adhesion test


Hair strength Water content


quantification/hydration Keratin content quantification Optical profilometry


Scanning electron microscopy (SEM)


Atomic force microscopy (AFM)


Transmission electron microscopy (TEM)


Optical Coherence Tomography (OCT)


Infrared Spectroscopy (IR) Raman Spectroscopy


Water absorption ability


techniques are summarised in Table 1. As several techniques can be applied


according to the desired evaluation or to the hair product submitted to clinical tests, for the purpose of this article, some of the most recent and/or used ex vivo methodologies are introduced below.


Hair care products As stated previously, the composition and


B Parameter/ Protocol Mean force to comb Angle of static hair after combing


Angle and area of hair tress exposed to high RH room


Angle and area of hair tress exposed to high RH room


SI content


Split ends imaging scored by expert according to five-category scale


Number of broken hair collected after standard combing


Hair colour fading by UV exposure Colour of hair exposed to UV Colour of hair exposed to


consecutive washing procedures


% area of hair surface covered in particles


Maximum force to break Water denaturation enthalpy


Lipid content quantification Content of methyl eicosanoic acid (18-MEA) on the hair surface


Roughness of the hair surface


Hair structure imaging scored by expert, according to a 12-point grading scale


Hair structure imaging Hair structure imaging


Hair structure imaging


Structural and morphological changes on the hair structure


Chemical and morphological changes on the hair structure


Hair tresses weight variation as indicator of % of water retained on hair tresses


Equipment/ technique Texturometer TA.XT


Hair apparatus with a 360° protractor


High RH room + photographs + image analysis software


High RH room + photographs + image analysis software


X-ray fluorescence spectrometer


Brightfield microscope Olympus CX31 + Clinical score


Combing apparatus Colorimeter® CL400 Colorimeter® CL400


Nikon MZ1500 zoom stereomicro- scope + image analysis software


Texturometer TA.XT Differential scanning Calorimeter


Keratin denaturation enthalpy Differential scanning Calorimeter ToF-SIMS IV (Time-of-flight


secondary ion mass spectrometry) Zeta-20 optical microscope


SEM + clinical score


AFM TEM


Optical Coherence Tomography (OCT)


IR Raman spectroscopy Weighing balance + centrifuge


structure of the hair fibre can suffer damage when the hair fibre is exposed to physical and chemical agents. The use of compounds quantification, such as time-of-flight secondary ion mass spectrometry (ToF-SIMS) or imaging analyses techniques, such as optical profilometry or scanning electron microscopy, allows us to understand the behaviour of the hair fibre structure and, therefore, the damage condition.8


ToF-SIMS to evaluate hair surface damage ToF-SIMS is a surface-sensitive analytical method that is able to detect chemical species present at low concentrations (i.e. ppm, ppb) as well as the spatial and/or depth distributions of the species.10 The lipids present on the hair surface are the first to be destroyed when damage occurs and, due to the high sensitivity level of this technique, it is possible to detect this degradation, even when the alterations of the cuticle are not visible.11 One known lipid present on the outermost hair


Figure 2: (a) 2D image of a virgin hair fibre; (b) 2D image of chemically damaged hair fibre (bleached hair) obtained by optical profilometry


PERSONAL CARE October 2022


surface is the methyl eicosanoic acid (18-MEA), and it plays an important role in hair surface hydrophobicity as well as in hair smoothness


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HAIR CARE PRODUCTS - HAIR DAMAGE PROTECTION / REPAIR


HAIR STYLING


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