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Cream
A cream is a formulation that contains water and oil and is stabilized
with an emulsifier. Lipophilic creams are called water-in-oil (W/O)
emulsions, and hydrophilic creams oil-in-water (O/W) emulsions. The
cream base for W/O emulsions are normally absorption bases such as
vaseline, ceresin or lanolin. The bases for O/W emulsions are mono-,
di- and triglycerides of fatty acids or fatty alcohols with soaps,
alkyl sulphates or alkyl polyglycol ethers as emulsifiers.
Creams can restore a disrupted hydrolipid film or due to their occlusive
effect rehydrate the horny layer. They can act as cleansing substances,
skin-protecting agents and as vehicles for therapeutic substances.
Shower Balm
EucerinŽ pH5 Cream Shower Balm is the name of an oil-in-water
shower emulsion with a particularly high lipid content (74%). At the
same time, surfactants ensure that the oils (lipids) are emulsified,
making additional emulsifiers superfluous. The Shower Balm lathers
easily and, because of its high lipid content and low surfactant content,
is particularly well-tolerated by the skin.
Emulsions
An emulsion is defined physically as a liquid system with two fluids
that are insoluble or only sparingly soluble in each other, and in
which one is finely dispersed within the other. Cosmetically and therapeutically
used emulsions consist of a polar water phase and a nonpolar oil phase.
There are oil-in-water (O/W) emulsions and water-in-oil (W/O) emulsions.
The necessary stabilization is achieved during production by the introduction
of an emulsifier which reduces the surface tension between the two
phases. Emulsions are of great importance for dermatological and cosmetic
products, as they meet the physiological demands of the skin and permit
uniform distribution of water-soluble and oil-soluble substances.
phase. In water-in-oil (W/O) emulsions the reverse is true.
Fatty ointments (rich ointments)
Fatty ointments are water-free, spreadable ointments that consist
of a solid structure-giving component and a fluid component. They
cover the skin with a fatty film that reduces the loss of water from
the skin surface by occlusion and thus enhances the skin's moisture
content. This improves the tension (tone) and water balance (turgor)
of the skin. Fatty ointments are used to protect dry skin from the
cold and to remove cosmetics. |
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Oil-in-water (O/W) emulsions
have an inner oil and an outer water phase. In water-in-oil (W/O)
emulsions the reverse is true.
1 Oil phase
2 Water phase |
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Follicle
Targeting System (see Liposomes)
The term "follicle targeting system" describes a liposomal formulation
that facilitates the transport of active ingredients (e.g. lactic
acid) into the follicle.
Cream gels (see also Hydrodispersion gel)
Cream gels are gels without an emulsifier, which - unlike hydrodispersion
gels - display the properties of a cream.
Gels (see also Hydrodispersion gel)
Gels are normally transparent, uniform, easily deformed dispersed
systems consisting of at least two components. Of the two components,
one is a fluid acting as a dispersing agent and the other a structure-giving
component, normally a solid colloidal material. This stabilizes the
fluid part by forming a three dimensional network.
Depending on the dispersant, there are different types of gel:
 hydrogels
(fluid = water)
alcohol gels
(fluid = alcohol)
lipogels (fluid
= liquid fats, e.g. paraffin)
surfactant
gels (fluid = water/surfactant mixture)
Hydrogels and alcohol gels have a distinct cooling effect due mainly
to the evaporation of the water or alcohol. For this reason they are
especially good for the production of sungels.
The structure-giving component can be either organic or inorganic,
hydrophilic or lipophilic, synthetic or natural. An example of organic
structure-giving components is cellulose derivatives that are mostly
used in film-forming protective gels. Polyacrylic acid, which has
a marked penetration effect, is used in alcohol gels. Lipogels, which
are mainly used as bases for ointments, find polyethylene a suitable
structure-giving component. |
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Inorganic structure-giving
components are bentonite (aluminium silicate) and colloidal silicic
acid. These display thixotropic properties, which means that, as highly
viscous gels, they liquefy without any change in the water content
under the influence of mechanical stress, for example, by stirring
or shaking. When the stress is removed the high-viscosity state returns.
Urea (see also Active and inactive ingredients)
Urea is one of the most important end products of human protein metabolism.
It has been used for many years in the treatment of chronic dry skin
conditions, as it is a very effective natural moisturising factor.
Urea is a colourless and odourless substance that is solid at room
temperature. There are no dangers in its application as it is non-toxic
and barely reactive. In prescribed formulations urea is regarded as
a "problem substance": urea is weakly hygroscopic and coarsely crystalline,
sometimes lumpy and not easy to pulverize. If used in a water-free
ointment, a sandpaper effect could arise when applied to the skin.
However, in formulas containing water, the urea dissolves in the cream's
water phase. |
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However, the stability
of urea is somewhat of a problem: in water-containing formulas that
are stored for a long time, urea can decompose into carbon dioxide
and ammonia. This can cause the pH to increase as high as 9. These
problems have been solved in pharmaceutical preparations by the inclusion
of suitable stabilizers such as sodium lactate. The decomposition
of urea into ammonia is minimized and the quality of the product is
guaranteed.
Urea - emulsion type and penetration kinetics
Besides the special galenic properties, the choice of emulsion
type plays a central role in achieving the sought-after effects of
urea preparations. The penetration of the active ingredient is dependent
on the degree to which the urea is set free from the ointment or cream
(liberation), as well as the penetrating power of the emulsion. Urea
is released more quickly and in a higher concentration from an oil-in-water
(O/W) emulsion than from a water-in-oil (W/O) emulsion. Even after
a long penetration period, most of the urea is found in the upper
layers of the stratum corneum. The release of urea from W/O emulsions
takes longer, but it penetrates in greater amounts into the skin and
is more evenly distributed.
The differing penetration kinetics as a function of the ointment base
is of therapeutic importance: The application of urea in O/W emulsions
and lotions achieves, at first, a higher degree of hydration (immediate
effect). However, using W/O emulsions as a vehicle for urea leads
to a more intensive and longer lasting increase in the water-binding
capacity of the horny layer (stratum corneum). The therapeutic efficacy
of urea in W/O emulsions is enhanced by the occluding effect of W/O
emulsions.
Hydrodispersion gel (see also Cream gels)
Hydrodispersion gels are a new development in formulations, which
make it possible to intersperse certain substances normally only soluble
in oil or water as micro-droplets within each other and without the
addition of emulsifiers and preservatives, for example, in a highly
effective sunscreen preparation.
Liposomes
Liposomes are phospholipid vesicles and permit targeted active ingredient
transport, e.g. into the follicle. This mode of action is particularly
important in follicle-associated conditions, such as acne.
Lotions
Lotions are liquid emulsions of the type water-in-oil (W/O) and oil-in-water
(O/W) in which medical and cosmetic active ingredients are included.
Due to their ability to spread easily, they are often used in body
care.
Oil baths (film-forming oil versus emulsion oil
bath, 2-phase oil bath)
Oil baths are often used particularly in the treatment of neurodermatitis.
They reduce skin dryness and irritation, and alleviate itching. The
lipid-replenishing properties of oil baths and their anti-pruritic
effect are temperature-dependent and best at 32 degrees Celsius.
Film-forming oil baths
Film-forming oil baths are emulsifier-free and form a lipid film on
the surface of the bath water. This clings to the skin when stepping
out of the bath and locks the moisture in the fully hydrated stratum
corneum. Film-forming oil baths have a strong lipid-replenishing effect
on the skin and markedly reduce transepidermal water loss (TEWL),
but have no cleansing effect.
Emulsion oil baths
In emulsion oil baths, hydrophilic emulsifiers sometimes present in
large quantities achieve a homogeneous distribution of the oil components
throughout the bathwater. The hydrophilic emulsifiers have a certain
cleansing effect, but at the expense of conditioning properties. The
higher the emulsifier content, the lower the lipid-replenishing effect.
2-phase oil bath
A 2-phase oil bath combines the properties of a film-forming oil bath
and an emulsion bath, achieving a dual effect, 2-phase lipid-replenishment:
Phase 1 (emulsion effect): The high proportion of oil, evenly
distributed in the finest droplets throughout the bathwater, replenishes
lipids during bathing.
Phase 2 (film-forming effect): A film of oil forms on the surface
of the bathwater and clings to the skin when stepping out of the bath,
forming a protective coating. In this way, the skin is able to store
the moisture taken up during the bath.
Oils
In dermatology, oils, sometimes called "fatty oils", refer to the
group of glycerol fatty acid esters which can include besides fatty
acid glycerol esters, triglycerides or triglyceride mixtures, also
lipoids, vitamins and colorants. Characteristic of oils is that they
are liquid at room temperature. They are divided into vegetable and
animal oils.
Natural oils, especially in emulsified form, are absorbed well into
the skin and thus stabilize the barrier function. For this reason,
they are used in skincare products. However, natural oils suffer from
oxidative decomposition. Therefore they are usually stabilized with
antioxidants.
O/W emulsion (oil-in-water ~)
If the skin condition is normal, or subacute dermatoses are present,
an oil-in-water (O/W) emul-sion is generally to be preferable. In
this form of emulsion, the preparation's oil droplets lie inside the
water phase. O/W emulsions are quickly absorbed into the skin, leaving
no oily shine. They are especially easy to spread. When applied to
the skin, the water part evaporates, causing a cooling effect. The
inner oil phase moisturises and oils the skin. O/W emulsions are only
lightly occlusive. They wash off with water and are suitable as cleansing
emulsions and for normal daily care. |
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Urea as a natural moisturising factor |
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Electron microscope image
of an oil-in-water (O/W) emulsion.
1 Outer water phase
2 Inner oil phase |
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Electron microscope image
of an oil-in-water (O/W) emulsion with an increased oil content.
1 Outer water phase
2 Inner oil phase |
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O/W emulsion with an
increased oil content
Oil-in-water (O/W) emulsions with an increased
oil content are quickly absorbed, spread easily and contain a high
proportion of caring lipids. They provide a cooling effect through
the evaporation of the water phase. |
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Ointments
The German Pharmacopoeia (DAB) defines anhydrous
one-phase bases, e.g. a water-free pure fat phase, as ointments.
By contrast, two-phase systems (water and fat) are called creams.
Ointments therefore consist of an ointment base (hydrocarbon, hydrodispersion,
lipo, hydro, or silicone gel), which may contain finely dispersed
active ingredients for use on the skin or mucous membranes.
Sprays, e.g. EucerinŽ Deodorant Spray Balm
and EucerinŽ Protective Spray 20
These are spray-on preparations, e.g. oil-in-water
emulsions with no added alcohol or preservatives, produced according
to the PIT (phase inversion temperature) principle. Using this technology,
specific active ingredients can be integrated into fine droplets,
known as nanodroplets, in the oil-in-water emulsion.
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W/O
emulsion (water-in-oil ~)
If the skin condition is dry or chronic dermatoses are present,
water-in-oil (W/O) emulsions are preferable. Here the inner phase
consists of water droplets and these are surrounded by the oil phase.
W/O emulsions are not as quickly absorbed into the skin. They leave
a protective oily film (occlusive effect). This film reduces the transepidermal
water loss (TEWL). It ensures an intensive skin moisturisation and
provides for a balanced oil-to-moisture ratio. Because of these features,
W/O emulsions are very effective in treating dry skin conditions.
They are suitable for the delivery of active ingredients into the
skin and cannot be washed out by water alone.
W/O emulsion, waterproof
Waterproof water-in-oil (W/O) emulsions are produced by a special
W/O emulsion technology. They are used extensively in sunscreen preparations
and thus prevent the active ingredients, UV filters for example, being
washed off by contact with water.
W/O emulsion, low water content
Medicated, low water content water-in-oil (W/O) emulsions have
a higher oil content than normal W/O emulsions. |
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Electron microscope image of a water-in-oil (W/O)
emulsion
1 Outer oil phase
2 Inner water phase |
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W/O/W
emulsion (water-in-oil-in-water)
Water-in-oil-in-water (W/O/W) emulsions are multiple emulsions,
in which oil droplets containing water droplets are themselves dispersed
in a surrounding water phase: As opposed to the classical O/W emulsion,
the inner oil phase itself has tiny water droplets interspersed within
it. This means the W/O/W emulsion has a 3-phase action: The outermost
water phase ensures an immediate moisturising of the upper skin layers.
In the second phase the oil droplets merge to form a layer, in the
third phase, the innermost water is continually released - in the
manner of timed-release capsules - and ensuring a long-lasting skin
moisturisation. |
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The water-in-oil-in-water (W/O/W) emulsion ensures
a long-lasting skin moisturisation.
1 Outermost water phase
2 Inner oil phase
3 Innermost water phase
4 Epidermis |
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