559 Prebiotic Micellar Solution
After 7 days of colonization in an antibiotic-free medium, no bacteria have been detected
on the skin explant surface of Group B. This group did not receive incubation treatment
except for a change in the culture medium. Its purpose in the study is to evaluate the
sterility conditions of the skin throughout the experiment to ensure the feasibility and
reliability of the test by observing the growth of unwanted microorganisms that could
mask the results obtained.
Despite their usefulness, skin cleansers’ potential impacts cannot be ignored. Disturbances
caused by hand hygiene practices, including soaps and cleansers, may disrupt protective
mutualisms in the skin microbiota, which allow invaders to colonize.20 In addition,
traditional hygiene practices, including the use of soaps and traditional cleansers, fail to
consider the high abundance of nonharmful and potentially helpful bacteria on the skin,
which may be disrupted by these products.21
S epidermidis, for instance, may act in reverse and prevent the colonization and proliferation
of S aureus in the human nostrils.22 This would make eradicating S epidermidis detrimental
to the host by facilitating the increased colonization of opportunistic pathogens.23 Moreover,
S epidermidis has been shown to produce antimicrobial peptides and modulate the host
immune response, which indicate its potential role in maintaining healthy host/microbiota
relationships.24
S epidermis is integral to maintaining the skin barrier function through the secretion of
sphingomyelinase, which assists the bacteria in nutrient acquisition and facilitates the host’s
production of ceramides. Furthermore, it enhances the expression of proteins related to
ceramide biosynthesis including claudin-1 and occluding.25 These ceramides are vital lipids
that contribute to moisture retention and safeguard the skin against environmental stressors.26
S aureus, in contrast, is the universal cause of boils, carbuncles, and skin abscesses and is
the agent generally identified as responsible for skin and soft tissue infections.27,28 S aureus
infections often begin as minor boils or abscesses and can progress to serious systemic
infections such as bacteremia and sepsis.29 Pre-existing conditions, such as injury (ulcers,
wounds) or tissue inflammation (exudative dermatitis), as well as underlying disorders (such
as diabetes mellitus or poorly controlled insulin-dependent cancer), are some of the risk
factors for infection with S aureus.27
S aureus also has a pivotal position in atopic dermatitis (AD) due to its ability to establish
intricate biofilms that considerably affect the integrity of the skin barrier and the host’s
immune response. The skin colonization by S aureus, especially in its biofilm state, is linked
to antibiotic resistance and dysbiosis, as the increased population of S aureus occurs to the
detriment of resident microbiota such as S epidermidis.30 This dysbiosis, along with the
dominance of S aureus, can intensify AD severity, thus rendering it an essential contributor
to the pathogenesis of the condition.31Therefore, skin cleansers must ensure the removal of
pathogenic microorganisms selectively that is, they must alter the population of commensal
microorganisms as little as possible. One of the ways to maintain the balance of the skin’s
microbiota is by using prebiotics, or ingredients that stimulate the growth and/or activity
of one or a limited number of microorganisms.32
The term prebiotic was initially developed to describe materials (carbohydrates) that reach
the colon when ingested and promote the growth of desirable organisms (probiotics). In
2017, the International Scientific Association for Probiotics and Prebiotics coined the current
definition of prebiotic as “a substrate that is selectively utilized by host microorganisms
conferring a health benefit.”33

560 JOURNAL OF COSMETIC SCIENCE
Examples of prebiotics include fructo-oligosaccharides, galacto-oligosaccharides,
glucomannans, oligosaccharides, inulin, isomalto-oligosaccharides, lactosucrose, lactulose,
palatinose, raffinose, sorbitol, xylitol, and xylo-oligosaccharides.29
In cosmetic formulations, prebiotics can be applied directly to the skin microbiota and
selectively increase the activity and growth of beneficial skin microbiota.29 The major
challenge in a cosmetic formulation containing prebiotics is the correct choice of components
to promote the growth of saprophytic or commensal (good) bacteria, such as S epidermidis,
to the detriment of pathogenic bacteria, such as S aureus.
To provide prebiotic properties, the prebiotic aqueous micellar solution presents a
combination of the polysaccharide inulin and xylitol. Inulin is a polysaccharide, like a
starch, that is available in the form of a white powder with a neutral taste.32 Inulin is used
as a functional ingredient in processed foods due to its primary characteristic: the b-(2,1)
bonds between fructose monomers cannot be digested by human intestinal enzymes. This
characteristic provides important applications in functional foods aimed at controlling type
2 diabetes, obesity, and other health conditions related to blood sugar. When ingested,
inulin passes through the mouth, stomach, and small intestine without being metabolized
until it enters the large intestine, where it is fermented by the colonic microflora. Inulin as
a prebiotic also stimulates the growth of beneficial bacteria in the colon, which increases
the absorption of important minerals such as calcium and magnesium and synthesizes
vitamins from the B-complex.32,34
Clinical studies have shown that daily administration of inulin increases the number of
Bifidobacteria and Lactobacilli in the colon while also reducing the number of Clostridia,
Bacteroidetes, and other nonspecific aerobic and anaerobic microorganisms.35 Related to
the activity of inulin in the digestive system, studies have shown that this carbohydrate
modulates the immune system, thus influencing the production of natural killer cells,
interleukins, and immunoglobin A.35 However, the scientific literature does not accurately
describe the clear role of topically applied inulin on the skin microbiota.
Xylitol, a naturally occurring five-carbon polyol (sugar alcohol), is used in several products
as a sugar substitute.36 It has beneficial effects for maintaining oral health when present
in chewing gum, including reducing the number of bacteria in saliva without altering
the oral microbial composition, while also providing an inhibitory action on the growth,
metabolism, and production of polysaccharides in Streptococcus mutans, the main causative
agent of dental caries.36
Regarding the topical application of xylitol, studies demonstrated that its association with
farnesol, a natural terpene found in essential oils that is commonly used in cosmetics and
perfumery to enhance sweet floral scents. It is also used as an antibacterial agent37 and has
acted selectively on the skin microbiota of patients with AD to prevent the formation and
dissolving of the biofilm formed by S. aureus, which selectively inhibits its growth,38 thus
indicating a selective action on the pathogen without influence on the resident microflora.39
CATHELICIDIN (LL-37) IMMUNOFLUORESCENCE ASSAY
This assay aims to evaluate the positive modulation of cathelicidin (LL-37), the one
exclusively human antimicrobial peptide, that acts as a defense molecule in the skin.40 The
results of the evaluation of cathelicidin protein expression for the test formula prebiotic
aqueous micellar solution are shown in Figures 4 and 5. The images demonstrate that