February 2017 happi.com happi • 51
DEFINING CLEAN SKIN
weakens the skin over time it, even if effective against bacteria,
may cause the skin to be more susceptible to infections.
Gojo Industries researchers recently published a study describing the effect of repeat exposure of ethanol to skin. In this
exploratory study, the effects of ethanol, isopropanol and n-propanol were assessed in vitro and in vivo. Significant differences
were observed between the three types of alcohols with ethanol
exhibiting the mildest, least barrier damaging of the three. In vitro, ethanol had the mildest effect on keratinocyte metabolism
and cytokine secretion. In vivo, panelists applied the alcohols 20
and 100 times a day for 14 days. No significant differences were
observed between the alcohols at the high application frequency.
However, at the low application frequency, n-propanol and isopropanol generated greater barrier impairment when compared
to ethanol as measured by TEWL and capacitance. The team concluded that ethanol-based sanitizers are better tolerated by skin.
While this study is missing the effect on skin microbiome and
the time of observation is limited to 14 days, it points toward a
potential correlation between skin condition and relevant skin
barrier biomarkers. Moreover, ethanol, while a strong antimicrobial agent, evaporates rapidly from the skin surface, and therefore
may exhibit a short-term effect that allows restoration of barrier
homeostasis. Industry should conduct more of these studies to
unravel the effect of skin cleansing regimens.
Skin cleansing practice should be studied with consideration of
skin barrier condition. The barrier should be assessed not only
physically by measuring transepidermal water loss (TEWL), but
also by other means that allow broader evaluation of its condition such as pH, a rapid recovery after stress, microbiome population, sebum secretion, and the presence of antimicrobial lipids
and peptides. These underlying skin conditions may not be visible clinically but are critical in the assessment of benefit vs. harm
in the overall evaluation of skin cleaning practice. Today’s measuring devices can evaluate endpoints and provide direction to
improve products and create new ones. Elements of a healthy
• Sufficient skin layers. A healthy barrier contains several layers of corneocytes structured as“brick and mortar,” with the cor-neocyte’s keratin being the“bricks” and the lamellar intercellular
lipids as the“mortar.”
• Proper ratio. The ratio of intercellular lipids/skin intercellular lipids exhibits a unique organization of lamellae in a thermodynamic phase that is rather rigid. The main components of
these lipids are ceramides, followed by cholesterol, saturated long
chain fatty acids and cholesteryl esters.
• Acidic pH. The pH of healthy skin is around 5-5. 5 and is
maintained by presence of fatty acids on the skin surface. Such
pH is essential to support a healthy skin microbiome.
• Relatively low levels of water. The upper layer of the skin,
the stratum corneum contains about 10% water. It is dry for a
reason. Elevating water contents in the skin artificially by either
occlusion or extensive use of moisturizers may support the environment for harmful biota.
• Sebum secretion. Human sebum is composed mainly of triglycerides and contains key elements of antimicrobial lipids that
balance harmful and commensal skin biota.
• Low transepidermal water loss (TEWL) as a measure of
healthy barrier. The lower the TEWL, the more intact the barrier.
A 2014 publication by Bouwstra’s research team explains the
importance of stratum corneum lipids in maintaining skin barrier.
Extensive use of products that deplete lipid barrier components
can lead to barrier impairment and changes that may facilitate
skin diffusion of pollutants and allergens. Another publication,
by Foweler and co-authors from the University of Louisville, explains that skin cleansing products can damage the stratum corneum, leading to barrier dysfunction. Any regimen that generates
a constant chronic imbalance to a healthy skin barrier, whether
it includes an antiseptic agent or not, can trigger a skin disease
and further exposure to harmful agents from the environment. A
healthy skin needs no extra means of cleansing or moisturization.
Over-cleansing and over-protection can generate a new state of
imbalance that the skin must “correct.” In recent decades there
is documented growth in population that reports to have“sensi-tive skin,” which may be due to adaptation of a Western lifestyle
that includes changes in nutrition, emotional stress, pollution
The CDC gives good old bar soap a big hand.