Ageing effects on the diameter, nanomechanical properties and tactile perception of human hair

The Trotter collection: A review of Mildred Trotter's hair research and an update for studies of human variation

OBJECTIVES

Mildred Trotter was an anatomist and physical anthropologist whose studies on hair morphology, growth, somatic distribution, and trait relationships to age and ethnogeographic population were foundational to the field of microscopical hair analysis. The collection of human hair samples she assembled for her research has been an underutilized resource for studies on human hair variation. We applied updated methods and reviewed Trotter's original data to reassess the relationship hair traits have to diverse population labels.

METHODS

Hair form and pigmentation patterns were measured from a subset of the hair samples accumulated by Trotter and we compared our data to Trotter's original results. Variability in hair traits were tested within individuals, within populations, and among ethnogeographic groups.

RESULTS

Measured hair cross-section dimensions and melanosome density and distribution revealed substantial variability within individuals and ethnogeographic populations. Hair traits were found to not be distinctly separable by ancestry but instead showed continuous variation across human populations. Trotter's measurements were precise and the dataset she compiled remains valid, though the conclusions should be reviewed in light of our current understanding of human variation.

DISCUSSION

Our findings support moving away from categorical ancestry classifications and eliminating the use of outdated racial typologies in favor of more descriptive trait analysis. Detailed analysis of trait pattern distributions are presented that may be useful for future research on human variation. We point to the need for additional research on human variation and hair trait relationships with reference to known population affinity.

In Vitro Biological Activity and In Vivo Human Study of Porcine-Placenta-Extract-Loaded Nanovesicle Formulations for Skin and Hair Rejuvenation

Porcine placenta extract (PPE) contains many water-soluble macromolecular compounds, such as proteins and growth factors, which have limited transportation through the skin. This study aimed to assess the effect of porcine-placenta-extract (PPE)-loaded nano-transdermal systems for skin repair and hair growth promotion. The potentials of the nanoformulation for cytotoxicity, cell proliferation, intracellular reactive oxygen species (ROS) reduction, lipoxygenase inhibition, intracellular inflammatory cytokine reduction, and cell aggregation were evaluated. PPE-entrapped niosome nanovesicles were produced by thin-film hydration and probe-sonication methods, followed by incorporation in a skin serum formulation. The physicochemical properties of the formulation were examined, and the efficacy of the serum formulation was elucidated in humans. The results showed that PPE had no toxicity and was able to induce cell growth and cell aggregation. In addition, PPE significantly decreased intracellular ROS, inhibited lipoxygenase activity, and reduced the production of intracellular tumor necrosis factor-α. In the in vivo human study, the PPE nanovesicles-loaded serum could improve skin properties by increasing skin hydration. Moreover, it was capable of promoting hair growth by increasing hair elongation and melanin index after application for one month. Consequently, the PPE nanovesicles-loaded serum was effective for skin anti-aging and hair rejuvenation.

Effects of Cosmetic Emulsions on the Surface Properties of Mongolian Hair

In the light of clean beauty and sustainability requirements emerging in the personal care market, the urgent need for the replacement of silicones in hair conditioners-with comparable performance and customer experience-has been highlighted in the industry. In this context, the goal of the present study was to investigate the physical effects of different silicone-free conditioner formulations on Mongolian hair after damage due to bleaching and compare the results to property changes induced by a classical silicone-containing formulation. To that end, the morphology, structure, and composition of strands and individual fibers of this hair type were characterized before and after bleaching by means of optical microscopy, atomic force microscopy (AFM), and X-ray photoelectron spectroscopy (XPS). It is shown that oxidative bleaching causes significant damage to the native hair surface, leading to local depletion or even large-area removal of the outer hydrophobic lipid layer. This results in enhanced wettability of the bleached hair by water (as confirmed by contact angle measurements) and is accompanied by an undesired loss of hair gloss and softness. Upon treatment with suitable cosmetic emulsions, the natural hydrophobicity of intact Mongolian hair can be partially or fully restored, with silicone-free formulations having effects similar to those of established silicone-containing products. The successive influence of bleaching and conditioning was further monitored using inverse gas chromatography (iGC), a technique that probes changes in surface energetics and polarity over an ensemble of an entire hair strand through interactions with specific molecules at the solid/gas interface. The resulting data mirror the macroscopic behavior of the bleached/conditioned hair and provide a quantitative scale for measuring damage and repair effects. Most notably, the effect of bleaching and subsequent conditioning on the haptic perception of hair strands could also be quantified with the aid of a biomimetic measurement system, which identifies increased friction (both tactile and sliding) as the major cause for the strawy feel of bleached hair and indicates successful relubrication after treatment with suitable conditioner formulations. Finally, the different physical properties determined for native, bleached, and reconditioned Mongolian hair are found to be reflected in application-oriented tests, namely in vitro measurements of wet and dry combing work. Overall, the data collected in this work shed novel light on the surface properties of Mongolian hair and highlight that effective hair conditioning after damage can be achieved without silicones in advanced cosmetic emulsions based on octyldodecyl myristate and glyceryl oleate.

Tribology of an assembly of hairs: Influence of multiscale surface chemistry and structure on sensorial tactile properties

BACKGROUND

Hair fibers may be either oriented in a common direction or randomly arranged. Fiber arrangement as well as cosmetic treatment control the sensorial perception. The present study explores the respective influence of these two aspects by predicting the product performance in terms of tactile perception.

MATERIALS AND METHODS

Friction forces between hair swatches of different curl patterns using a finger-like probe have been measured to better mimic real-life hair/finger contact. Measurements of fiber alignment, hair diameter (thickness), and compression tests were performed on natural and treated swatches to assess the respective weight of these parameters.

RESULTS

Conditioned hair exhibit an adhesive behavior measured at the start of the frictional movement. Conversely, natural hair is influenced by fiber reorientation. After a few seconds, friction-related signals stabilize. Thus, the averaged friction forces do not only depend on hair thickness, but increase with a decreased alignment of the fibers.

CONCLUSIONS

Intrinsic (diameter/curliness) and external (orientation/ friction/compression) characteristics allow to define a model of "macroscopic" roughness linked to the sensorial characterization. As friction of hair swatches depends upon fiber alignment and coating, this combined approach is potentially a very useful in vitro test, as an alternative or complementary method to sensory tests.

Age, lifestyle and self-perceptions of hair: Is there an association with hair diameter and tensile properties?

OBJECTIVE

To determine the association of age, lifestyle habits and the self-perception of hair condition with the objectively measured physical properties of hair in Caucasian females with brown hair.

METHODS

Hair biophysical properties, lifestyle habits data and self-perceptions of hair condition were collected on 110 Caucasian females with brown hair ranging in age from 17 to 78. Hair diameter (cross-sectional area) and tensile properties (elastic modulus, break strength and break extension) were measured at the root end of individual fibres (n = 100/subject) from the crown and frontal regions using objective instrumental methods. Other measures included body mass index (BMI) and Savin female pattern hair loss grades based on judging of standardized front, top and side view head images. Lifestyle habits and practices and self-perceived hair condition were obtained via a standardized self-assessment questionnaire.

RESULTS

Hair fibre diameter and break extension decreased significantly with age. Hair fibre elastic modulus and Savin hair loss scores increased significantly with age. No age-related change in hair fibre break stress was observed. A history of smoking or being overweight was significantly associated with having lower hair fibre cross-sectional area but was not associated with any of the measured tensile properties. Subjects who perceived their hair as fine, thinning or weak had significantly lower cross-sectional areas than subjects who did not. Subjects who perceived their hair to be healthy or strong had significantly higher cross-sectional areas than subjects who did not.

CONCLUSION

The biophysical properties of hair change significantly with age. A history of smoking or being overweight was significantly associated with having smaller hair cross-sectional area but was not associated with differences in hair tensile properties. The self-perception of having strong or healthy hair seems more associated with having a larger cross-sectional area than any real differences in hair strength.Abstrait.

Incubatory environment of the scalp impacts pre-emergent hair to affect post-emergent hair cuticle integrity

OBJECTIVES

To determine whether the oxidative stress transmitted to newly grown hair from an unhealthy scalp has physical consequences to the cuticular condition and function.

METHODS

A uniquely designed 24-week clinical study included 8 weeks of pretreatment with a cosmetic shampoo and 16 weeks of treatment with either a potentiated zinc pyrithione (ZPT) antidandruff shampoo or a placebo cosmetic shampoo. This clinical design allowed the growth and acquisition of hair samples under conditions of varying but known scalp health as a result of treating a dandruff/seborrheic dermatitis (D/SD) population. Two complementary methods were used to characterize the integrity of the cuticular surface. Hair surface hydrophobicity was assessed by quantifying water wetting force using a Wilhelmy balance method. Surface structure and porosity were assessed using dynamic vapor sorption (DVS) to gravimetrically quantify water sorption.

RESULTS

Chemical oxidative stress to pre-emergent hair has been shown to have negative consequences to hair surface structure. Compared to a placebo shampoo control, use of a potentiated ZPT shampoo improved scalp health and significantly improved the following attributes associated with healthy hair: hair surface hydrophobicity (surface energy) and cuticular moisture barrier effectiveness (dynamic vapor sorption).

CONCLUSIONS

Pre-emergent hair can be negatively impacted by the oxidative stress that occurs with an unhealthy scalp, possibly due to metabolic activity of resident microbes. Manifestations of the oxidative stress include altered cuticle surface properties that are responsible for its protective function; these effects are similar in type to those observed by bleaching post-emergent hair. These alterations have the potential to make the hair, once emerged from the scalp, more susceptible to the cumulative physical and chemical insults responsible for hair feel and look, fiber integrity, and overall retention.