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Background and Introduction
What Is Already Known?
■ First connections between altered quantitative
and/or qualitative bacterial growth in pathologi-
cally modified skin and the shifted skin pH were al-
ready made by those who coined the term acid
mantle. At that time, the physiologic role of the
acid skin surface was thought to be a protective
mechanism against invading organisms.
■ The understanding of the skin pH has broadened,
and we know that the acid character and its gradu-
al change within the skin also help to orchestrate
epidermal differentiation and corneocyte shedding
and many other cellular functions, for example, in
pigmentation, ion homeostasis, epidermal (stem)
cell behavior, and so on.
What Does This Text Add?
■ In some controlled trials (acne, atopic dermatitis,
incontinence-associated dermatitis, aged skin), the
benefits of targeted skin acidification have become
evident and the use of topical preparations with
reduced pH may therefore be recommendable.
■ The formulation concepts for direct acidification
are based on a reduced pH of the hydrophilic prod-
uct phase in combination with a buffering system
with a sufficiently high buffering capacity within
the vehicle.
Abstract
Ninety years ago – in 1928, the term acid mantle was
coined by the physicians Heinrich Schade and Alfred Mar-
chionini in Kiel, Germany. A decade later Marchionini and
several coworkers published 5 scientific communications
in the Klinische Wochenschrift on “Der Säuremantel der
Haut und Bakterienabwehr” (acid mantle and defense
against bacteria). They described experimental detail,
documented age- and body site as well as skin disease-
dependent skin pH shifts, and discussed the significance
of the pH and bacterial growth on the skin. In their fourth
and fifth communication, they made the first connection
between the altered quantitative and qualitative bacte-
rial growth in pathologically modified skin and the shift-
ed skin pH and attributed it partly to the gap in the acid
mantle (pathologische Lücke des Säuremantels). They
Surber C, Abels C, Maibach H (eds): pH of the Skin: Issues and Challenges.
Curr Probl Dermatol. Basel, Karger, 2018, vol 54, pp 1–10 ( DOI: 10.1159/000489512 )
The Acid Mantle: A Myth or an Essential
Part of Skin Health?
Christian Surber a, b · Philippe Humbert c · Christoph Abels d · Howard Maibach e
a Department of Dermatology, University Hospital, Basel , and
b Department of Dermatology, University Hospital, Zurich ,
Switzerland;
c Department of Dermatology, University Hospital, Besançon , France;
d Dr. August Wolff GmbH & Co. KG Arzneimittel,
Bielefeld , Germany; e Department of Dermatology, University of California San Francisco, San Francisco, CA , USA
Downloaded from http://karger.com/books/book/chapter-pdf/1987930/000489512.pdf by University of Basel user on 17 June 2024
2 Surber · Humbert · Abels · Maibach
also investigated the pH of several topical dermatologic
preparations and concluded that their benefit can at least
partly be attributed to their acid character and recom-
mended the systematic investigation of acid treatments
in dermatology. At that time, the physiologic role of the
acid skin surface was thought to be a protective mecha-
nism against invading organisms. Hence, it seemed rea-
sonable to allocate protection to an easy and conceivable
term such as “mantle.” Today, “acid mantle” as a term is
still a very suitable metaphor to illustrate the protective
quality of the “acid” in the skin and the term has become
part of colloquial speech. In the meantime, our under-
standing of the skin pH has broadened, and we know that
the acid character and its gradual change within the skin
also help to orchestrate epidermal differentiation and
corneocyte shedding. For many more biochemical pro-
cesses within the skin, the compartmental pH is crucial,
for example, in pigmentation, ion homeostasis, epider-
mal (stem) cell behavior, and so on. The often existing
difference between the H
+ concentration of extra- and
intracellular as well as subcellular compartments estab-
lishes an ionic, electric, and/or osmotic driving force;
hence, H
+ concentration per se acts as an extra-, intra,-
and subcellular signaling modality affecting and control-
ling many cellular functions. One may even consider pH
a universal signal and effector. It is therefore also no sur-
prise that skin pH shifts have been observed in various
skin pathologies. More recently, in carefully controlled tri-
als (acne, atopic dermatitis, incontinence-associated der-
matitis, aged skin), the benefits of targeted skin acidifica-
tion have become evident and the use of topical
preparations with reduced pH may be recommended.
The currently prevailing formulation concepts for direct
acidification are based on a reduced pH of the hydrophil-
ic product phase in combination with a buffer with a suf-
ficiently high buffering capacity within the vehicle.
© 2018 S. Karger AG, Basel
The acid character of the skin’s outer surface was
first mentioned at the end of the 19th century and
decades later – in 1928 – vividly described as the
acid mantle. From that period until today, the un-
derstanding of the importance of the acid charac-
ter of the skin for skin barrier integrity has tre-
mendously increased. “Acid mantle” as a term
has become a very suitable metaphor to illustrate
the protective quality of the “acid” in the skin. To-
day, the term is broadly used and has become part
of colloquial speech. In particular, the advertising
industry has popularized the term to promote
cleansing means that simultaneously protect or
restore the acid mantle. In the general population,
there is also a widespread belief that excessive
scrubbing of the skin destroys the acid mantle.
Against this background, it is legitimate to ask
the question whether the term “acid mantle”
stands for a myth or an essential part of skin
health. Within the scope of this paper, we explore
the acid-base concept from the past to this day,
discuss the key communications of Schade and
Marchionini
[1] who coined the term acid man-
tle, examine the potential to influence the acid
character of the skin by application of topical skin
products, and finally address the challenges to
quantitate the acid character of the skin.
The Acid-Base Concept
Today, the terms acids/acid and bases/alkaline
are ordinary components of our colloquial lan-
guage and are often used in technical, biochemi-
cal, and medical contexts. To most of us, the
terms are more common in connection with nu-
trition. Everyone has a concept of acid (vinegar,
lactic acid in sour-milk, citrus fruits, etc.) and al-
kaline (alkaline foods [“deacidification for
health”], spring water, etc.) and the wellness and
spa industry propagate and offer both acid and
alkaline foods and balneotherapies.
Originally, the concepts of acidity came from
the ancient Greeks who defined “sour-tasting”
substances as oxein, which metamorphosed into
the Latin word for vinegar acetum , which became
anglicized to acid. Acid substances were eventu-
ally found not only to taste sour but also to change
the color of litmus paper and corrode metals. In
Surber C, Abels C, Maibach H (eds): pH of the Skin: Issues and Challenges.
Curr Probl Dermatol. Basel, Karger, 2018, vol 54, pp 1–10 ( DOI: 10.1159/000489512 )
Downloaded from http://karger.com/books/book/chapter-pdf/1987930/000489512.pdf by University of Basel user on 17 June 2024
The Acid Mantle 3
contrast, bases were typically defined and studied
by their ability to counteract acids – and thus fol-
lowed behind the acids in their chemical charac-
terization. Their more rigid terminology (alka-
line) is derived from an Arabic root word associ-
ated with “roasting” because of the fact that the
first bases were characterized from the soap-mak-
ing substances obtained from roasting ashes and
treating them with water and slaked lime. In the
early 14th century, the Spanish scholar, Arnaldus
de Villa Nova (1235–1311), began to use litmus
for studying acids and bases. This compound, ex-
tracted from a lichen, had been used as a dye since
at least the time of the Vikings, but he was the first
person known to use it as a test of acidity. This
idea was expanded by Robert Boyle (1627–1691),
who found that certain plant-derived substances
changed color in the presence of acid or basic sub-
stances. One example was a liquid fraction of vio-
lets, which is blue in a pH neutral environment
but turns green when exposed to bases and red
when mixed with acid
[2, 3] .
The first scientific concept of acids and bases
– originally based on mass analysis or titrimet-
rics – was proposed by Antoine Lavoisier (1743–
1794) in the 1770s. His knowledge of strong ac-
ids was mainly restricted to oxoacids such as ni-
tric acid and sulfuric acid. He defined acids in
terms of their containing oxygen, which in fact
he named from Greek words meaning “acid-for-
mer” (from the Greek οξυς (oxys) meaning
“acid” or “sharp” and γεινομαι (geinomai) mean-
ing “engender”). Other theories followed, for ex-
ample, Liebig’s hydrogen theory of acids. This
definition was based on the chemical composi-
tion of organic acids, finishing the doctrinal shift
from oxygen-based acids to hydrogen-based ac-
ids. Justus von Liebig’s (1803–1873) definition,
while completely empirical, remained in use for
almost 50 years until the adoption of the Arrhe-
nius definition. The first modern definition of
acids and bases in molecular terms was devised
by Svante Arrhenius (1859–1927). The hydrogen
theory of acids led to Arrhenius receiving the
Nobel Prize in Chemistry in 1903. An Arrhenius
acid is a substance that dissociates in water to
form hydrogen ions (H
+ ); that is, an acid increas-
es the concentration of H
+ ions in an aqueous
solution. This causes the protonation of water or
the creation of the hydronium (H
3 O + ) ion. Thus,
in modern times, the symbol H
+ is interpreted as
a shorthand for H
3 O + because it is now known
that a bare proton does not exist as a free species
in aqueous solution. An Arrhenius base is a sub-
stance that dissociates in water to form hydrox-
ide (OH
– ) ions; that is, a base increases the con-
centration of OH
– ions in an aqueous solution.
Later, the Danish chemist Johannes Brønsted
(1879–1947) and the English chemist Thomas
Lowry (1875–1936) independently proposed a
modification of the definitions, retaining the con-
nection of the proton release to acids but defining
bases more broadly as any substance capable of
binding protons. Thus, measurements of the hy-
drogen ion became key to defining the level of
acidity, and bases truly were relegated to the mir-
ror-companion of acids as simply receptors. The
above definitions, relying on protons and hy-
droxyl ions as it did, generally related to reactions
in water solution. Gilbert Lewis (1875–1946) re-
fined the acid and base concept to include disso-
lution events in nonaqueous solvents, where free
protons are not involved. Developing along with
these theoretical considerations, the practical
measurement of acidity became the foundation of
analytical chemistry and ultimately of the analyt-
ical instrument business. The concept of pH was
perhaps the most important in facilitating this
evolution. It was the work of Hermann Walther
Nernst (1864–1941) that, in 1889, gave the theo-
retical foundation for the use of electrode poten-
tial to measure the concentration of an ion in so-
lution. With Arrhenius’s definition of acidity as
the result of hydrogen ion concentration, a scale
of acidity based on the results of electrode poten-
tial was created. In 1909, Søren Peter Lauritz Sø-
rensen (1868–1939) developed a new colorimet-
ric assay for acidity
[4] . But more importantly, he
Surber C, Abels C, Maibach H (eds): pH of the Skin: Issues and Challenges.
Curr Probl Dermatol. Basel, Karger, 2018, vol 54, pp 1–10 ( DOI: 10.1159/000489512 )
Downloaded from http://karger.com/books/book/chapter-pdf/1987930/000489512.pdf by University of Basel user on 17 June 2024
4 Surber · Humbert · Abels · Maibach
defined the concept of expressing acidity as the
negative logarithm of the hydrogen ion concen-
tration, which he termed pH. And he was one of
the first to attempt the use of electrostatic meth-
ods to discern pH. The usefulness of his pH con-
cept was first recognized by Leonor Michaelis
(1875–1949). He published a monograph – “Die
Wasserstoffionenkonzetration” – that helped to
convince biochemists and later chemists and oth-
ers of the critical importance of pH to analytical
research
[5] . From then on, measurement of pH,
especially in the life sciences, was considered of
increasingly greater importance. The modern
measurement of pH was revolutionized by 2 ma-
jor innovations. The first was the development of
a superior glass electrode capable of responding
to hydrogen ions. The second occurred when Ar-
nold Beckman (1900–2004) invented a sensitive
and sturdy acidometer that used a pair of vacu-
um-tube signal amplifiers and glass electrodes to
monitor fruit acidity during the production of
pectin and citric acid. The original Beckman ac-
idometer became the inspiration for many im-
provements and adaptations in what would uni-
versally be known as the pH meter, giving pro-
found impetus to the rise of the international
equipment business. For example, the Swiss engi-
neer Bertold Suhner (1910–1988) developed one
of the first European pH meters for Metrohm,
only a few years after Beckman introduced his de-
vice
[6–9] .
The Acid Mantle
In the second part of the 19th century, sweat was
subject to intense research and the question
whether sweat was acid or alkaline was a central
question that had controversy and was intensely
debated upon. In a comprehensive paper in the
journal Monatsheft für praktische Dermatologie ,
Ernst Heuss – a scholar of Prof. Dr. Paul Gerson
Unna (Hamburg) – described the experimental
procedures to determine the acid and alkaline
character of sweat and skin colorimetrically
[10] .
He provided conclusive evidence that fresh sweat
and the skin surface were acidic. He presumed
that lower parts of the skin were less acidic, con-
currently admitting that he had experimental dif-
ficulties to conclusively prove his assumption. In
the years to come, the evidence for the acid char-
acter of the skin including a pH gradient within
the skin (from acid toward neutral) was finally
substantiated
[11–14] .
In 1928, Heinrich Schade and Alfred Marchio-
nini reported results of their investigation of the
reaction of the sweat. They confirmed the obser-
vations made by Heuss and others and added data
from their own pH measurements from cadaver
and living skin. It is interesting to note that they
then discussed the experimental challenges of
cleansing the electrode and skin and also the pH
shifts in diluted and concentrated sweat and point
out that the measurement of the pH is possible
only when the skin is sufficiently moist. For dry
skin, they suggested the use of a mist spray. They
also mentioned that the use of acid skin prepara-
tions may influence skin pH. With the title of
their paper “Der Säuremantel der Haut” (the acid
mantle of the skin), they coined the term “the acid
mantle” of the skin, which has become an easy-to-
understand term for everybody
[15] . In 1930,
Scholtz confirmed and expanded Schade’s and
Marchionini’s observations. He tested several
acid topical treatments (e.g., sour mild) and rec-
ognized the significance of acid preparation in re-
lapse prevention
[16] .
In the years 1938 and 1939, Marchionini et al.
[17–21] published 5 scientific communications in
the Klinische Wochenschrift on “Der Säureman-
tel der Haut und Bakterienabwehr” (acid mantle
and defense against bacteria). They describe ex-
perimental details, give references related to their
instrumentations, document age- and body site as
well as skin disease dependent skin pH shifts, and
discuss the significance of the pH and bacterial
growth on the skin. In their fourth and fifth com-
munication, they make a connection between the
Surber C, Abels C, Maibach H (eds): pH of the Skin: Issues and Challenges.
Curr Probl Dermatol. Basel, Karger, 2018, vol 54, pp 1–10 ( DOI: 10.1159/000489512 )
Downloaded from http://karger.com/books/book/chapter-pdf/1987930/000489512.pdf by University of Basel user on 17 June 2024
The Acid Mantle 5
altered quantitative and qualitative bacterial
growth in pathologically modified skin and the
shifted skin pH and attribute it partly to a patho-
logic gap in the acid mantle (pathologische Lücke
des Säuremantels). They also investigated the pH
of several topical dermatologic preparations and
concluded that their effect can at least partly be
attributed to their acid character and recommend
the systematic investigation of acid treatments in
dermatology. It is interesting to note that Mar-
chionini, Schade or Scholz did not explicitly ex-
plain why they coined the term “acid mantle”
[15–21] . The designation “acid mantle” has be-
come a plain metaphor to illustrate the protective
value of the acid character of the skin and is now-
adays used colloquially. However, Öhman and
Vahlquist question the term and call it a misno-
mer because it implies something that can readily
be removed from the skin (take off the coat/man-
tle), for example by cleansing
[11] .
After the pioneering work of Marchionini,
Schade, and Scholz, the number of investigations
on pH and its effect on skin has steadily grown to
the present day
[22–27] .
It was also observed that skin partially resist
acid/alkaline aggression. This led to the develop-
ment of the alkali/acid resistance test – used in the
1960s – to detect workers who are likely to de-
velop occupational diseases in certain chemical
work environments. A mild variation of the al-
kali/acid resistance tests, also called the acid/al-
kali neutralization test, assesses how quickly the
skin is able to buffer applied acids or bases with-
out the occurrence of skin corrosion. Repetitive
applications of acid or base demonstrated that the
skin’s buffering capacity is limited and may be
overcome. It has been postulated that amino acids
and sweat are responsible for the buffering capac-
ity. Data suggest that the buffering capacity of dif-
ferent skin layers differ substantially from each
other. This observation could further improve
our understanding related to issues in dermato-
pharmacology and toxicology. When the buffer-
ing capacity becomes nonexistent, the pH of skin
becomes significantly altered, thereby initiating a
series of processes within the skin with positive
(wound healing) and negative (inflammation) ef-
fects
[28–32] .
Originally, the physiologic role of an acid skin
surface was thought to be a defense mechanism
against invading organisms. More recently, it has
been demonstrated that several key processes in-
volved in the synthesis and maintenance of a
competent skin barrier are affected by pH and its
gradient within the epidermis
[13, 33–35] . For a
number of biochemical processes within the skin,
the compartmental pH is crucial, for example, in
pigmentation, ion homeostasis, epidermal (stem)
cell behavior, and so on. The often existing differ-
ence between the H
+ concentration of extra- and
intracellular as well as subcellular compartments
establishes an ionic, electric, and/or osmotic driv-
ing force; hence, H
+ concentration per se acts as
an extra-, intra-, and subcellular signaling modal-
ity affecting and controlling many cellular func-
tions. One may even consider pH a universal sig-
nal and effector
[36–39] . It is therefore also no
surprise that skin pH shifts have been observed in
various skin pathologies. There are reports on the
relationship between skin surface pH and preva-
lence of skin diseases
[40–43] and the compro-
mised barrier function and properties in aged
skin have been attributed to pH-dependent alter-
ations in the activity of key enzymes involved in
the biochemical processing of the skin lipids, the
formation of the lipid bilayers, and corneodesmo-
some degradation
[35] . Therefore, it seems obvi-
ous that the exogenous acidification by means of
topically applied formulations may offer preven-
tive or therapeutic benefits.
Topical Influencing of the Skin Surface pH
The use of liquid or semi-solid wash-off or leave-
on preparations to clean or treat the skin has a
long tradition. The term “cleanser” – first men-
tioned in 1955 in Medline – is most often used in
Surber C, Abels C, Maibach H (eds): pH of the Skin: Issues and Challenges.
Curr Probl Dermatol. Basel, Karger, 2018, vol 54, pp 1–10 ( DOI: 10.1159/000489512 )
Downloaded from http://karger.com/books/book/chapter-pdf/1987930/000489512.pdf by University of Basel user on 17 June 2024
6 Surber · Humbert · Abels · Maibach
connection with removing make-up, dead skin
cells, oils, dirt, and other types of pollutants from
the skin of the face
[44] . Today, the term is used
in a more general way. Based on the anticipated
beneficial effects of acidification of the skin, it be-
came popular to develop slightly acid cleansers to
add an additional benefit to the cleansing prod-
ucts
[44, 45] . Nowadays, soap-free, skin-friendly
cleansers are most often commercialized with
slightly acid or physiological pH values ( ≈ 5.5).
Despite the fact that the majority of investigations
confirmed the benefits, some conflicting investi-
gations exist. Duncan et al.
[46] demonstrated
that a product used (pH 5.5) in routine skin care
significantly affected the skin pH of ICU patients
but not the bacterial colonization. In a long-term
study (5 years), Takagi et al.
[47] found that the
continuous use of a soap-based cleanser did not
affect the pH-maintaining mechanism of human
skin. From the beginning on, it was also clear that
additional factors than just pH may affect local
tolerance
[48–51] .
More recently, the potential of semi-solid
leave-on products to “correct” the skin surface
pH and hence to accelerate barrier recovery, to
maintain, or to enhance barrier integrity has
again attracted attention (note that Scholz already
reported in 1930 the potential of acid treatments
of skin diseases
[16] ) [52–56] . The studies consis-
tently showed accelerated barrier recovery and
enhancement of the barrier integrity and proper-
ties. By means of tape-stripping the stratum cor-
neum, Behm et al.
[54] also reveal the data that the
pH in the deeper layer of the skin (stratum granu-
losum) was actually lowered after the use of a pH
4 O/W emulsion with sufficiently high buffering
capacity. Indications such as incontinence-asso-
ciated dermatitis or atopic dermatitis are medical
highly relevant skin conditions with a great level
of affliction that urgently need treatment options.
Products for targeted skin acidification may offer
in these indications new therapeutic options
[56–
58] . However, further clinical trials with larger
cohorts are necessary to strengthen these find-
ings. Important issues related to formulation
composition (acids), buffering systems used, or
buffering capacity of product and product dosing
have so far not been directly addressed.
pH and Buffering Capacity of Topical
Formulations
The first and main objective of all developments
of pharmaceutical and cosmetic formulations is
the stability of the active principle and the formu-
lation as a whole. Decisive factors are the physi-
cochemical compatibility of all substances used in
the formulation. In terms of activity and stability,
the pH and the buffering capacity of the hydro-
philic phase also play a key role. Based on the pH
partition hypothesis, that is, the nonionized spe-
cies of an acid or a basic molecule is more perme-
able across biological barriers than the ionized
formulators will pH-optimize the formulation to
increase the non-ionized species of the active
principle
[59, 60] . Furthermore, the activity (e.g.,
preservatives) and stability of many vehicle ingre-
dients are pH dependent. To maintain an optimal
pH in the formulation and hence to ensure prod-
uct safety and stability during shelf live, buffering
systems are added.
Because product development is generally fo-
cused on product stability, it may happen that the
optimal product pH is different from the physio-
logic skin surface pH (4.5–5.5)
[61–63] . Shi et al.
[62] determined the pH of hydrophilic phase of
31 skin care products sold in the United States
(2012). Eighteen products from important brands
showed a pH between 5.5 and 8.2. No informa-
tion on the buffering capacity was given and
hence it is difficult to estimate the potential im-
pairment of the skin surface pH. However, it is
understandable that the long-term use of skin
care products (leave-on product) with elevated
pH impairs the skin. In a recent investigation,
Wohlrab and Gebert
[61] determined the pH and
the buffering capacity of the hydrophilic phase of
Surber C, Abels C, Maibach H (eds): pH of the Skin: Issues and Challenges.
Curr Probl Dermatol. Basel, Karger, 2018, vol 54, pp 1–10 ( DOI: 10.1159/000489512 )
Downloaded from http://karger.com/books/book/chapter-pdf/1987930/000489512.pdf by University of Basel user on 17 June 2024
The Acid Mantle 7
66 cosmetic skin care products from the German
market. Only 43% of the evaluable products
showed a pH of <5.5 and may therefore be con-
sidered appropriate for the treatment of skin with
impaired barrier function or for topical skin acid-
ification. Three products specifically developed
for the acidification of the skin showed a buffer-
ing capacity >1. The majority of products had a
low or very low buffering capacity.
The significance of pH and buffering capacity
for product stability and quality is well known
and part of every galenic product development
plan. However, the targeted development of
products with a specific pH and buffering capac-
ity for skin acidification to accelerate barrier re-
covery to maintain or to enhance barrier integrity
has gained only some attention from developers,
patients, and consumers. Exceptions exist; see the
section above: Topical Influencing of the Skin
Surface pH
[52, 56] .
Measurement of Skin Surface pH
The first investigations dealing with the degree of
acidity on skin surface were made by way of colo-
rimetry
[10] . Accuracy was limited and the appli-
cation impractical. In their basic work on skin pH,
Schade and Marchionini
[15] used an electrome-
tering device – the quinhydrone electrode (redox
electrode). First experiments with “flat” glass elec-
trodes
[64, 65] were reported in 1938. Their use has
become the current standard and since then
brought together an enormous amount of infor-
mation on skin surface pH as a function of endog-
enous, exogenous, and environmental factors.
Since the beginning of skin surface pH recording,
some authors repeatedly point out that the pH
measurement and the measurement process per se
represent major challenges. In the last decade,
some groups have taken the effort to develop
guidelines for the in vivo assessment of skin surface
pH and made recommendations for measure-
ment, measurement interpretation, and data re-
porting to promote a more universal/standardized
methodology to be followed, which if done would
make comparison of data possible
[66, 67] . How-
ever, the relevance of the various experimental
conditions still remains unclear and has not been
investigated in detail. Already Schade and Mar-
chionini in 1928 mentioned the difficulties with
the pH measurement in connection with the rins-
ing of the electrode and the skin. This and many
other issues have been addressed in the guidance
though more systematic testing is urgently needed
to better understand the pH measurement of the
microenvironment itself between the glass elec-
trode and the skin. Too little attention is devoted to
the fact that the measurement represents only the
pH of the microenvironment between the glass
electrode and the skin and may therefore be differ-
ent from the actual skin surface pH or the pH of the
underneath layers. It is therefore advisable to bear
in mind that the use of any topical products may
significantly affect the measurement
[68] . This ap-
plies also to the water including its quality that is
applied for skin surface pH measurement. The po-
tential “aging” of the electrodes and its relevance to
measurement quality is also an area in need of in-
vestigation to improve guidance. In the future, ma-
jor efforts are needed to evaluate these and other
potentially relevant factors to further improve the
measuring certainty.
Other approaches for the measurement of the
skin surface pH have been proposed (e.g., micro-
electrodes, pH-sensitive fluorescent dyes fol-
lowed by confocal laser microscopy, or electron
spin microscopy imaging). However, these have
not yet become routinely operational
[11, 12, 69–
72] .
Conclusion
The importance of the acid character of the skin is
well documented. Deviations from the physiolog-
ical norm – whether causative or as a result of dis-
turbance – entail some sort of skin barrier impair-
Surber C, Abels C, Maibach H (eds): pH of the Skin: Issues and Challenges.
Curr Probl Dermatol. Basel, Karger, 2018, vol 54, pp 1–10 ( DOI: 10.1159/000489512 )
Downloaded from http://karger.com/books/book/chapter-pdf/1987930/000489512.pdf by University of Basel user on 17 June 2024
8 Surber · Humbert · Abels · Maibach
ment. Under normal conditions, an ingenious
buffering system in the skin ensures a perpetual
normalization of the acid character of the skin.
Right from the very beginning of research in
the field, researchers discussed opportunities and
limitations to shape the acid character of the skin
to protect the skin and to accelerate barrier recov-
ery, to maintain, or to enhance barrier integrity.
With the introduction of skin cleansers in the
1950s, the awareness for the importance of the
acid character of the skin reached large parts of
the population. The metaphor “acid mantle”
played a major role in popularizing skin cleans-
ers.
More recently, the benefits of targeted skin
acidification have become clinically evident and
the use of topical preparations with reduced pH
(direct acidification) is being recommended. The
currently prevailing formulation concepts for di-
rect acidification are based on a reduced pH of
the hydrophilic product phase in combination
with a buffer with a sufficiently high buffering
capacity. Important issues related to formulation
composition (acids), buffering systems used, or
the buffering capacity of product and product
dosing have so far not been systematically inves-
tigated. Incontinence-associated dermatitis or
atopic dermatitis is a medical and a highly rele-
vant skin condition causing a great level of afflic-
tion that urgently needs treatment options. Be-
cause of these indications, products for targeted
skin acidification may therefore offer new thera-
peutic options.
A matter of some concern is that the quantifi-
cation of the acid character of the skin is techni-
cally very delicate and standardization and vali-
dation still incomplete. The existing guidance re-
quires further work. Furthermore, many existing
publications report incompletely the experimen-
tal conditions.
The term “acid mantle” was coined by those
who first recognized the importance of the acid
character of the skin. The physiologic role of the
acid skin surface was thought to be a protective
mechanism against invading organisms. Hence, it
seemed reasonable to allocate protection to an
easy and a conceivable term such as “mantle.”
Since then, our understanding of the skin pH has
tremendously broadened. The acid character and
its changes within the skin help to orchestrate epi-
dermal differentiation and corneocyte shedding.
Today, the acid character of the skin is recognized
as a key requisite for healthy skin. Against this
background, it is still legitimate to keep this meta-
phor even 90 years after its creation.
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Prof. Dr. phil. nat. Christian Surber
Department of Dermatology
University Hospital Zurich, Gloriastrasse 31
CH–8091 Zurich (Switzerland)
E-Mail christian.surber@unibas.ch
Surber C, Abels C, Maibach H (eds): pH of the Skin: Issues and Challenges.
Curr Probl Dermatol. Basel, Karger, 2018, vol 54, pp 1–10 ( DOI: 10.1159/000489512 )
Downloaded from http://karger.com/books/book/chapter-pdf/1987930/000489512.pdf by University of Basel user on 17 June 2024
