62 BODY CARE
skin, and the detector. The latter can be either an instrument or the eye of an observer. All the techniques used for skin
colour evaluation take these factors into consideration. Numerous methods have been validated to evaluate skin lightening effects. Visual assessment with rating scales and clinical scores are the oldest methods but are still widely used in the cosmetic industry. Despite being subjective (although this can
be improved by an appropriate training), their advantages lie in their simplicity and closeness to the expectations from the consumers who expect a visible lightening. Objective evaluation of the efficacy of depigmenting treatments for the armpit area is desirable. Many instruments are commercially
available for such purpose. Spectrophotometers analyze either the whole absorption or reflectance spectrum from the skin or only some absorption peaks specific of chromophores such as haemoglobin or melanin. In the latter case, a melanin index can be determined. Chromameters or colorimeters analyze the colour of the reflected light by using three sensors that are designed to simulate the human eye sensitivity with regards to the blue, green and red primary colours. The Luminance L* and the Individual
Typological Angle calculated from RGB values are very sensitive indicators of a lightening effect. Another methodology usable for skin colour measurement relies on cross-polarized digital photography. The red, green and blue values constituting digital pictures can be mathematically converted to the L*a*b* colour space. Therefore the Luminance L* and the Individual Typological Angle colorimetric parameters can be determined. In our laboratory, we often use Antera 3D
(Miravex, Ireland). This is an imaging system that not only captures images of the skin surface and of the underlying layers, but also creates three-dimensional representations of the skin. As shown in Figure 1, haemoglobin and melanin distributions, texture, folds and pores are some of the axillary skin features assessable with this device. Quantitative analysis of these parameters makes Antera 3D camera a valuable tool for monitoring skin changes in cosmetic studies. Finally, a more recent technology,
hyperspectral imaging, acquires images across a broad spectrum of wavelengths (from infrared to ultraviolet potentially) unlike standard RDG digital cameras that record only three colour channels. Each pixel in a hyperspectral image contains both spatial and detailed spectra information. This enables the access to structural, biochemical and physiological characteristics of the skin that are otherwise invisible to the human eye. Applications of hyperspectral imaging
to skin studies are numerous. With regards to axillary skin, it allows to assess skin pigmentation and map melanin distribution. Measuring skin oxygenation, blood flow and erythema by detecting haemoglobin absorption at specific wavelengths is another important application since it gives a tool to
PERSONAL CARE April 2025
monitor cutaneous irritation and inflammation. Assessing skin hydration, collagen and
elastin fibres is also possible. Due to the variety of biological information obtained, hyperspectral imaging has already become a powerful tool for skin research.
A few other in vivo assessments of axillary skin condition To conclude this short review of axillary skin problems and their evaluation methods, it is worth mentioning that some methods used to remove hair, such as shaving or depilatory products, can induce skin irritation.8
All the
methods dealing with colour measurements cited above can be used as tools to evaluate the degree of irritation caused by diverse armpit treatments. As the skin in the underarm region can
exhibit increasing laxity as a function of age, some persons may seek rejuvenation and tightening treatments to improve skin tone and elasticity. Some well known non-invasive methods can be used to investigate the response of the skin to these interventions. Cutometry is one of the best-known technique from cosmetic scientists.
Conclusion Nowadays, many countries worldwide require
manufacturer to provide scientific data to support efficacy claims. For axillary skin care cosmetics, as for other products used on the face
or other body parts, there is no method universally adopted by the personal care industry. Companies can use their
own methodologies as long as they meet the necessary standards of proof. In the domain of cosmetic
claim substantiation, understanding skin biology and the physiological, anatomical, morphological and functional changes occurring following a given treatment is the mandatory
prerequisite to design an efficacy study and select the appropriate evaluation method. Therefore, we hope that the presentation of some of the most common available
techniques could be useful for the readers who will have some days to choose one method to investigate the efficacy of a new cosmetic formulation for skin care.
PC
References 1. Lanzalaco A et al. A comparative clinical study of different hair removal procedures and their impact on axillary odor reduction in men. Journal of Cosmetic Dermatology. 2015; 15, 58-65
2. Piérard GE et al. EEMCO guidance for the efficacy assessment of antiperspirants and deodorants. Skin Pharmacology and Applied Skin Physiology. 2003; 16: 324-342
3. Szeimies RM et al. Long-term efficacy and safety of 1% glycopyrronium bromide cream in patients with severe axillary hyperhidrosis: results from a phase 3b trial. Journal of the European Academy of Dermatology and Venereology. 2023; 37: 823-830
4. Teerasumnran P et al. Deodorants and antiperspirants: new trends in their active agents and testing methods. International Journal of Cosmetic Science. 2023; 45: 426-443
5. Maxeiner B et al. Design and application of a screening and training protocol for odour testers in the field of personal care products. International Journal of Cosmetic Science. 2009; 31: 193-199
6. ASTM E1207-14(2022). Standard guide for sensory evaluation of axillary deodorancy
7. Bouabbache S et al. Exploring some characteristics (density, anagen ratio, growth rate) of human body hairs. Variations with skin sites, gender and ethnics. International Journal of Cosmetic Science. 2019; 41: 46-54
8. Evans RL et al. The impact of different hair removal behaviours on the biophysical and biochemical characteristics of female axillary skin. International Journal of Cosmetic Science. 2020; 42: 436-443
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