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Moisturizers in the skin care

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					                        Moisturizers in the skin care
                     published in Beauty Forum 2011 (3), 86-88 and 2011 (4), 46-49

The term moisturizer generally stands for moisturizing creams. The present overview
will inform on components that influence the skin hydration.


T
     errestrial organisms have developed a                     skin wrinkles. Excessive increase of the skin
     number of strategies to protect against                   hydration with the help of occlusive waxes and
     dehydration and certain death. Mother                     hydrocarbons is not recommended as it only
Nature has optimized cell membranes, cell                      causes skin swellings and subsequently leads
components and the skin barrier in this regard.                to disorders within the skin structure. Tradi-
                                                               tional anti-wrinkle creams are based on this
•    Aquaporins are peptides that are inte-                    principle: they remove minor wrinkles via
     grated into the cell membrane. They con-                  swellings.
     trol the transport of water and specific sub-             The skin hydration is easy to measure with a
     stances, as e.g. glycerin, through the cell               Corneometer®. It basically is a flat condenser
     membranes. Aquaporins can be stimulated                   whose capacity is modified and measured via
     by various substances, such as vitamins.                  the dielectric medium water. The minimal tis-
•    Bacteria protect themselves against dry-                  sue penetration of the Corneometer® only al-
     ness with water-retaining substances,                     lows statements on the surface layers of the
     against cold with substances that inhibit                 stratum corneum. The transepidermal water
     the formation of ice crystals and against                 loss (TEWL) is the equivalent of the quantity of
     temperature rises with materials that im-                 water evaporated through the skin in form of
     pede the denaturing of proteins. Examples                 vapor. It is used as a measure for the perme-
     here are ectoin and diglyceryl phosphate.                 ability and the condition of the skin barrier.
•    Amphibians have their body surfaces                       The sebum activity influences the TEWL and
     covered with mucus in order to retain wa-                 that is why the measuring of skin hydration and
     ter for a considerable time. Animal mucus                 sebum allows conclusions on the transepider-
     mostly consists of glycoproteins (combina-                mal water loss, some experience is required,
     tion of proteins with carbohydrates) while                though. This is helpful for skin analyses in
     vegetable mucus consists of polysaccha-                   summer when the TEWL will yield more or less
     rides. Also the leaves of succulents con-                 inaccurate readings.
     tain high concentrations of mucus. Aloe
     vera can be mentioned here as an exam-                    Skin barrier and TEWL
     ple.
•    The human stratum corneum has effective                   The majority of emulsifiers used interferes with
     barrier layers which impede the loss of                   the layered structure of the skin barrier and
     water. They consist of long chained cera-                 increases the TEWL. As a consequence, they
     mides, cholesterol and fatty acids.                       are frequently combined with hydrocarbons or,
•    The NMF (Natural Moisturizing Factor)                     in other words, with paraffins and mineral
     of the human skin consists of a multitude                 waxes which again reduce the TEWL with their
     of water retaining substances, in particular              impermeable surface film. Evidence of the
     amino acids.                                              barrier disordering effect of emulsifiers is the
•    The sebum of the skin seals the skin                      wash out effect which means that the natural
     surface with lipid substances, such as                    lipids of the skin are washed out with skin
     squalene, in order to reduce the evapora-                 cleansing. Today’s moisturizing creams refrain
     tion of water.                                            from emulsifiers or contain emulsifiers that
                                                               quickly metabolize in the skin.
Measurement of skin hydration                                  Many substances have an indirect effect on the
                                                               TEWL. Among them is linoleic acid (essential
The purpose of moisturizing creams is to stabi-                fatty acid) or linoleic acid providing vegetable
lize the regular skin hydration of the individual              oils. Linoleic acid serves as a substrate for
person. In terms of measurement, the effects                   barrier active ceramide I. A deficit in essential
of the creams can be evaluated by reading the                  fatty acid shows by dry and scaly skin.
skin hydration and the transepidermal water                    Other substances directly influence skin hydra-
loss (TEWL), however, it can also be visually                  tion or TEWL by binding water molecules. This
validated by observing the behavior of little dry

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Moisturizers in the skin care                                                                          page 2 of 4


capacity is due to the hygroscopic (water at-                  done carbonic acid (PCA) belongs to the
tracting) functional groups.                                   amino acids and is a popular component in
                                                               skin care products. Amino acids belong to the
•    Hydroxy groups (-OH): alcohols, glycols,                  group of osmolytes. This term stands for sub-
     glycerin, saccharides (sugar) etc.                        stances that are able to compensate concen-
•    Carboxy groups (-COOH): organic acids                     trations in the skin and hence stabilize the
     and their salts                                           individual osmotic pressure. Malfunctions of
•    Polyethylene glycols (-O-CH2-CH2-)n: for                  this control system may cause irritations after
     details on PEGs please refer to Kos-                      the application of water-containing skin care
     metische Praxis 2009 (1), 12-15                           products, an effect which can be compared to
•    Amino groups (-NH2, -NH-): amines,                        irritations caused by sweat, whose salts con-
     amino acids                                               centrate while drying and build up hypertonic
•    Amide groups (-CO-NH2, -CO-NH-): urea,                    properties.
     allantoin, fatty acid amides, peptides, pro-              Carbomers (polyacrylates) are consistency
     teins etc.                                                agents and remain on the skin surface. They
•    Metal ions: magnesium (Mg2+), calcium                     have no moisturizing capacities but may
     (Ca2+). They are so-called cationic acids                 slightly reduce the TEWL due to their perme-
     with hygroscopic features and should only                 able film. Combined with penetrating moistur-
     be applied in chelated form (e.g. in combi-               izers, they have synergetic effects and improve
     nation with AHA acids). Otherwise there is                their efficacy in low atmospheric humidity. In
     a certain risk that they react with the skin              this regard, it can be stated from experience
     barrier and cause disorders of the layered                that they also reduce sensations of tension.
     structure. Insoluble salts like magnesium                 Ceramides are basic components of the bar-
     or calcium palmitate or –stearate have no                 rier layers of the skin and a base element of
     influence on skin hydration and remain on                 laminary-structured DMS creams. They are
     the skin surface.                                         frequently gained from yeast.
•    Mineral salts: sodium and potassium salts                 Cholesterol occurs in the skin barrier and can
     of the phosphoric acid (phosphates), hy-                  be replaced in creams by phytosterols with
     drochloric acid (chlorides) and sulfuric acid             similar structure (as e.g. from avocado oil or
     (sulfates)                                                shea butter). The barrier activity is stimulated.
                                                               CM-Glucan is a chemically modified filming
Popular active agents                                          polysaccharide which impedes the evaporation
                                                               of water through the skin and which can ab-
Algae extracts: In combination with specific                   sorb and release moisture (hydration buffer).
proteins, amino acids and mineral salts, the                   Diglyceryl phosphate (DGP) is an osmolyte
alginic acid in the extracts increases the skin                which suppresses the denaturing in thermo-
hydration. Liposomal laminaria digitata extract                philic bacteria at higher temperatures. The
sprayed on the closed eyelid may be beneficial                 substance also inhibits the collagen degrada-
against dry eye syndrome.                                      tion caused by matrixmetalloproteinases.
Alginic acid (alginate): The polysaccharide is                 D-panthenol: With its two alcoholic hydroxyl
gained from brown algae and consists of man-                   groups and its amide bond, the provitamin B5
nuronic and guluronic acid units. It is used as a              increases the skin hydration, has tightening
consistency agent and forms a moisture-re-                     effects and supports the cell formation.
taining film on the skin surface.                              Ectoin: The water retaining pyrimidine deriva-
Alginic acid hydrolysates are fractions of the                 tive increases the irritation threshold of the
alginic acid. The smaller the size, the better                 skin. It is used in products for the sensitive
they penetrate into the upper horny layer                      skin.
where they bind water just like any other short-               Glycerin is a component of the NMF and,
chained carbohydrates.                                         despite contrary reports, has no dehydrating
Allantoin has structural elements of urea;                     effects. Although hand creams with a high
hence it also supports the skin hydration and                  content of glycerin visibly augment the skin
eliminates itching as well.                                    hydration, the major part of the glycerin as well
Aloe vera: The gels of aloe vera are rich in                   as natural skin components are again released
amino acids, polysaccharides and mineral                       from the skin during hand cleaning. The skin
salts, among others. They have anti-inflam-                    then feels dehydrated. Hence, creams with a
matory effects and form moisture-retaining                     high fat and moderate glycerin content are
films on the skin.                                             more appropriate for the hand care.
Amino acids are the most important elements                    Glyceryl glucoside: The combination of gly-
of the natural NMF. They have excellent water-                 cerin and glucose is a natural substance, binds
retaining effects and are a natural protection of              water and stimulates aquaporin 3. There is a
the skin against nitric oxides (radicals). Pyrroli-

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Moisturizers in the skin care                                                                         page 3 of 4


multitude of analogous glycosides with similar                skin caring characteristics such as skin tight-
behavior.                                                     ening and moisture retention.
Glycols are bivalent (2 hydroxy groups) water                 Urea belongs to the NMF substances. Urea
retaining alcohols. Moderate concentrations of                can crack hydrogen bridges. Its keratolytic
glycols impede the growth of microorganisms                   activity in higher concentrations results from
similar to ethanol. The most popular repre-                   this specific property. Among other applica-
sentatives are propylene glycol, butylene gly-                tions, it is also a component of non-dehydra-
col, pentylene glycol and hexylene glycol.                    ting powders and suppresses itching.
Glycolic acid is the simplest alpha hydroxy                   Xanthan gum: The polysaccharide has thick-
acid (AHA) and its sodium and potassium salts                 ening characteristics and improves the lubri-
can be found in moisturizing creams.                          cating and glide properties of gels. It forms a
Hyaluronic acid, as one of the most popular                   surface film combined with pleasant skin tight-
high molecular moisturizers is active at the skin             ening effects and also retains moisture in the
surface. Together with phosphatidylcholine, hy-               skin.
aluronic acid is used to treat dry eye symptoms               Sugars (saccharides) retain water, however,
similar to algae extract. In skin care appli-                 their adhesive properties account for the fact
cations, hyaluronic acid extends the bandwidth                that they are not very popular. There are also
of low molecular moisturizers towards low                     products with honey additives.
atmospheric humidity.                                         Sugar substitutes: The 6-valent sugar alcohol
Lactic acid: The sodium salt of lactic acid                   sorbitol (sorbite) is a naturally occurring carbo-
(INCI: sodium lactate) is a component of the                  hydrate with water retaining properties similar
NMF and a rather effective moisturizer.                       to glycerin. In combinations with ethanol, gly-
Sodium chloride (table salt) only shows                       cols or glycerin, sorbitol has antimicrobial ef-
weak efficacy. Isotonic solutions (0.9% NaCl)                 fects in preservative free preparations without
and 3.5% sea salt solutions (mainly sodium                    sensitizing potential. Similar features show the
chloride) are used for baths for the sensitive                related mannitol (mannite) which occurs in
skin. Water of the Death Sea still shows higher               algae, beach or tideland plants, and the natural
concentrations: it contains considerable                      inositol (inosite) of the human body. Other
amounts of magnesium and calcium salts.                       sugar alcohols with comparable effects are
PEGs: Long chained PEGs (macrogols) form                      xylitol (xylite) and maltitol (maltite).
moist surface films on the skin. PEGs with alkyl
chains (emulsifiers) cause washing out effects.               The limits of efficacy
Attention should be paid to their sensitivity to
UV/atmospheric oxygen which leads to irrita-                  On the one hand, the skin hydration depends
tions of the skin.                                            on a functioning NMF, skin barrier and bal-
Phospholipids: Phosphatidylcholine (PC),                      anced sebum, but it is also determined by the
phosphatitylinositol (PI), phosphatidylethanol-               atmospheric humidity. The skin per se is capa-
amine (PE) and phosphatidylserine (PS) are                    ble of adapting to different conditions. In case
components of lecithin and increase the skin                  of a fast change of atmospheric humidity
hydration. PC temporarily also augments the                   between the interior of the house and the ex-
TEWL though, as it fluidizes the skin barrier                 ternal atmosphere, but also in case of skin
(effective principle of liposomal preparations).              disorders, the skin has more difficulties to
Native phospholipids contain linoleic acid                    adapt, which particularly applies to the mature
which is integrated into the ceramide I of the                skin. There are three simple rules to illustrate
skin barrier. Related to phospholipids are                    the effects:
sphingomyelins.
Polyglutaminic acid (PGA): The polypeptide                    •   When air with a relative humidity of 100%
is a filming agent with water retaining and                       at a temperature of 0° C is warmed up to
tightening characteristics.                                       10° C, it features an atmospheric humidity
Polysaccharides (polymer sugars): Many                            of about 50%. Warmed up to 20° C, the
filming cellulose derivatives such as hy-                         humidity is around 25%. The atmospheric
droxyethyl cellulose and hydroxypropyl cellu-                     humidity approximately halves with every
lose belong to this group (rf. Kosmetische                        10° C.
Praxis 2009 (4), 12-15).                                      •   The TEWL increases with decreasing air
Proteins of vegetable origin are used as base                     humidity.
substance for protein hydrolysates. Depending                 •   The efficacy of moisturizers decreases
on their manufacturing process, they contain                      with the decline of air humidity. There is a
protein fractions such as peptides or amino                       characteristic threshold for every mois-
acids. Protein hydrolysate serves as a starting                   turizer where it becomes inefficient and
material for condensates with fatty acids (pro-                   releases the moisture into the circumambi-
tein hydrolysate condensates) with excellent                      ent air.

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Moisturizers in the skin care                                                                          page 4 of 4


                                                               tion and possibly higher external temperatures
The following transitions stress the skin and                  the dosage of lipid substances including phy-
are particularly demanding for moisturizers:                   tosterols in skin care preparations should even
                                                               be increased. Sensitive dosing is required here
•    cold outside air    heated rooms with ex-                 to avoid both imbalances and undesired
     tremely low air humidity (Central European                swelling of the skin due to occlusion as well as
     winters)                                                  a disordered natural recovery of the skin. In
•    muggy outside air     chilly rooms with ex-               cases of rosacea skin, there even is an in-
     tremely low air humidity (air condition)                  creasing risk of creating the ideal living condi-
                                                               tions for the typical anaerobic bacteria that
In case of low air humidity, low molecular and                 cause the rosacea-specific blushing.
well penetrating moisturizers like urea, gly-                  Conclusion: Skin hydration is one of the most
cerin, glycols, salts etc. alone are unable to                 important factors for a healthy skin. In terms of
cope. Even frequent re-applications will not be                preventive measures, particular emphasis
beneficial in this context. On the contrary: In                should be laid on a stable skin barrier and the
this case, the moisturizers will concentrate in                preservation of the natural NMF. Externally
terms of hypertonic properties, which may lead                 applied and preferably physiological moistur-
to irritations of the skin particularly in case of             izers may be beneficial here.
rosacea-prone skin. The range of low molecu-
lar moisturizers can be enlarged by high mo-                   Dr. Hans Lautenschläger
lecular moisturizers like hyaluronic acid, CM-
Glucan and other filming agents. Filming                       Blue text passages are not contained in the
agents form an additional barrier for the TEWL                 original publication.
on the skin surface. With even lower air hydra-




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