SKIN MICROBIOME
53
Deodorant actives: bridging the development gap
Steffen Nordzieke, Florian Genrich, Beate Diesing, Ewa Maria Musiol-Kroll – Symrise
In our daily lives, we are exposed to many situations that can trigger sweating. Sweating is a natural reaction of the body to prevent it from overheating thus to control body temperature. Other causes for increased sweating could be emotional stress, illness, hormonal fluctuations, or even spicy food. Most people feel uncomfortable when
sweating and fear the sweat-associated odour that is unpleasant, not only for us but also for others. Visible armpit sweat and body odour both can be embarrassing and may even harm people’s self-confidence. Therefore, there is a huge demand for effective solutions in the form of antiperspirants and deodorants. According to Mintel, long-lastingness has been the global top claim for the last 15 years in new product launches in the deodorant category.1
Additional major needs
for deodorants from the consumer’s side are naturality and skin-friendliness.2 Manufacturers of finished deodorant
products prefer easy-to-process ingredients for two main reasons: to save cost and to reduce energy consumption. Developing new ingredients that combine all these features is challenging. To evaluate the effectiveness of deodorant
actives it is crucial to understand the formation of human sweat malodour. Originally, sweat is an odourless biofluid that is released by sweat glands in the skin. Sweat is composed of water (99%), ions
(e.g., potassium, sodium, and chloride ions), proteins, and tiny amounts of other components such as lipids. These compounds are a source of nutrients for the human natural microbiota. The metabolic activity of microorganisms assimilates the nutrients and degrades the initially odourless fluid into body odour that contains steroids, long-chain fatty acids, short- chain and medium-chain volatile fatty acids, and thioalcohols.3,4 The complexity of sweat malodour can be described by a three-dimensional (3D) complementary process: odourless fresh sweat and its complex components (I), skin microorganisms (MOs) that utilize the nutrients (II), and smaller metabolites produced by the MOs with low odour threshold (III). Traditionally, the strategy to formulate deodorants has been to apply antimicrobials and/or to use fragrances for masking the sweat malodour. Screening for suitable deodorizing molecules has usually been approached via determining
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minimal inhibitory concentrations (MICs) of test substances against specific key bacteria of the human axilla. Microplate tests have been proven useful in this process and are commonly utilized to perform medium to high throughput screenings of candidate substances. Screenings that are performed with selected
single MOs often turn out inefficient in the subsequent expensive in vivo studies as they ‘ignore’ the remaining members of the more complex human armpit microbiome. Ideally, all three dimensions of the complexity (I-III) should be covered. The use of natural sweat samples including the full spectrum of the armpit microbiota enables tracking of the conditions and time- dependent changes of the sweat composition. In our previous study, we presented such ex vivo models and demonstrated sweat odour development under natural conditions.5 Furthermore, we have shown how odour
develops when common deodorizing products are applied.6
Taking the next logical step, we
now report on new results from our ‘3D ex vivo model’ that combines microbiological, sensory, and chemical analyses.
For the first time, we are presenting the
use of our model for the development of a new deodorant ingredient, followed by its detailed efficacy investigation via in vivo studies against the untreated armpit, a placebo, and a benchmark product. This comprehensive analysis enabled us
to confirm the reliability of the prediction of our model. We are subsequently introducing a new cosmetic ingredient derived from this model: SymDeo® PMD green (INCI: Propanediol Caprate).
Materials and methods To evaluate the efficacy of potential deodorant ingredients and their influence on the microbiome, the “3D model” (ex vivo) combining microbiological, chemical, and sensory analyses was used and the resulting molecule was subsequently analyzed in an in vivo study. For the ex vivo analysis, fresh human sweat
of both axillae was collected from healthy female and male subjects (aged 31 – 65 years) after a ten-day washout phase (based on DIN EN ISO 9001:2015; Germany).
October 2024 PERSONAL CARE
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