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Description  |
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FIELD OF INVENTION
The invention relates to a water-in-oil emulsion suitable for topical
application to human skin and/or hair, to provide enhanced protection from
the damaging effects of sunlight. More particularly, the invention is
concerned with an exceptionally stable water-in-silicone oil emulsion
comprising a hydroxyalkanoic acid and an inorganic sunscreen, which
together with the silicone ingredients, provide a product having, in
addition to its sunscreen properties, exceptional cosmetic and sensory
properties aimed at improving the quality, particularly the plasticity of
skin to which it is applied, either as a beauty aid or in the treatment of
damaged or diseased skin.
BACKGROUND TO INVENTION & PRIOR ART
A soft, supple and flexible skin has a marked cosmetic appeal and is an
attribute of normal functioning epidermis.
As human skin ages with advancing years, the epidermis can become folded or
ridged or furrowed to form wrinkles which signal the loss of youthful
appearance and herald the transition to old age. This transition can occur
prematurely with young people, especially those who expose themselves to
excessive doses of sunlight. Also, the outer layer of the epidermis, that
is the stratum corneum, can become dry and flaky following exposure to
cold weather, or excessive contact with detergents or solvents which
result in loss of skin moisture with the result that the skin loses its
soft, supple and flexible characteristics.
Emollients such as fats, phospholipids and sterols have in the past been
used to soften wrinkled or dry skin, but it is apparent that these
emollients are only partially effective as a remedy for skin in poor
condition.
The use of 2-hydroxyalkanoic acids for enhancing the quality of human skin
following topical application thereto has already been described.
Thus, EP-A 0 007 785 (Unilever) discloses skin treatment compositions
incorporating .alpha.-hydroxycaproic acid or .alpha.-hydroxycaprylic acid
or mixtures thereof, the compositions having a pH value of less than 7,
usually from 2 to 4.
It is also proposed in U.S. Pat. No. 4,105,782 (Yu & Van Scott) to use
amines or ammonium salts of .alpha.-hydroxyacids in the treatment of acne
or dandruff and, in the Yu & Van Scott patents U.S. Pat. No. 4,105,783 and
U.S. Pat. No. 4,197,316, to use such compounds in the treatment of dry
skin. U.S. Pat. No. 4,234,599 (Yu & Van Scott) discloses the use of
.alpha.-hydroxyacids, and their esters or amine salts in the treatment of
keratoses. In U.S. Pat. No. 4,363,815 (Yu & Van Scott) it is proposed to
use .alpha.-hydroxyacids or .beta.-hydroxyacids or keto acids or their
derivatives, in a composition for treating skin conditions.
According to GB 1 471 679 (Avon), it is known to use alkali metal salts of
C.sub.2 -C.sub.5 .alpha.-hydroxycarboxylic acids in moisturising
compositions.
In DE 2 110 993 (Henkel), there are disclosed alkali metal salts of C.sub.4
-C.sub.10 .alpha.-hydroxycarboxylic acids, and the sodium salt of
.alpha.-hydroxycaprylic acid is mentioned.
In addition to premature ageing of human skin, as seen from the formation
of wrinkles, other more immediate damaging effects of sunlight on skin
have been observed since time immemorial, such as sunburn (erythema),
keratoses and increased incidence of skin cancer (carcinoma), and many
remedies have been proposed to protect the skin from this type of damage.
In general terms, harmful ultra-violet radiation, particularly that
originating from sunlight, which penetrates the upper atmosphere and
reaches the earth's surface, can be classified into:
i. the energy-rich UV-B rays (290-320 nm wavelength) which possess an
intense physiopathological activity on the skin; these are absorbed just
above the dermis and they are responsible for erythema and skin
pigmentation, and
ii. UV-A rays (320-400 nm wavelength) which penetrate deeper into the skin
(to the dermis and beyond). Their energy is much lower and the
photobiological effects they cause are much more long term in nature, for
example, they accelerate skin ageing. Certain organic substances
(sunscreens) whose molecules absorb the harmful ultra-violet rays have
been proposed for use; these substances mitigate the deleterious effects
of ultra-violet radiation.
Some of these substances absorb more effectively in UV-A range thereby
providing filtering of UV radiation in this range, while others are more
effective in the UV-B range.
A common problem exists, however, whatever the choice of organic sunscreen,
for protection from whichever wavelength of ultra-violet radiation, and
this is that physiological damage to the body can occur, following topical
application of these sunscreens in quantities necessary to provide
effective filtering of harmful ultra-violet radiation. Even those organic
sunscreens that are believed to be safe to use in this way, necessarily
have safety limits imposed, based on the quantity applied to the skin,
which can result in only moderate to poor protection from harmful
ultra-violet radiation.
Certain inorganic substances which physically block ultra-violet exposure
of the skin have also been proposed for use as sunscreens. Notable of
these is titanium dioxide having a very small particle size. This grade of
titanium dioxide, designated ultrafine (also described as micronised)
TiO.sub.2, affords a good degree of sun blocking potential without the
unacceptable skin whitening experienced with the normal pigmentary grade
(particle size >300 nm). For example, in DE-A-3824999 (The Boots Company
PLC), it is proposed to use titanium dioxide with a mean primary particle
size of <100 nm in a water-in-oil emulsion as a sunscreen preparation.
This reference also suggests that additional organic sunscreen agents,
such as p-aminobenzoic acid and esters thereof, methoxycinnamate,
benzophenone, dibenzoylmethanes or salicylates can also be included to
improve protection.
In spite of this and other prior proposals, there still exists a need for a
completely stable, highly efficient and thoroughly safe sun protection
composition which not only provides a wide spectrum of protection in the
ultra-violet region, against the aforementioned short and long term damage
to the skin that can result from excessive exposure to sunlight, but which
can also ameliorate or prevent skin damage following exposure to other
adverse climatic conditions or contact with, particularly immersion in
detergent solution liable to cause damage. It is with the fulfillment of
these needs that the invention is concerned.
SUMMARY OF INVENTION
It is apparent that some emulsions, such as classical oil-in-water
emulsions, containing a hydroxyalkanoic acid, such as 2-hydroxyoctanoic
acid, suffer from the disadvantage that they lack sufficient stability
over long periods of storage at temperatures that may vary from below
0.degree. C. to up to 45.degree. C., that is conditions to which such
emulsions can be subjected following manufacture and prior to sale and use
by the consumer. This is believed to be due at least partly to the
solubilisation of the hydroxyalkanoic acid by the emulsifiers
conventionally used in such products, with the consequence that separation
of oil and water phases can ensue.
A further consequence of this solubilisation is to release the
hydroxyalkanoic acid prematurely from the emulsion, so that its delivery
to the skin when the emulsion is applied topically is less efficient and
effective. The sensory properties of such emulsions can be poor, due to
the presence of the hydroxyalkanoic acid in the continuous phase. This
then exerts a dominating influence on the sensory profile, with the
consequence that residual stickiness on the skin can be experienced. Also,
where protection from the harmful effects of sunlight is required, these
emulsions are virtually ineffective unless loaded with one or more organic
sunscreens in an amount which can be dangerous to tender skin.
It has now surprisingly been found that a water-in-oil emulsion having the
aforementioned desired properties can be obtained by including in it a
2-hydroxyalkanoic acid, a polydimethylcyclosiloxane, a silicone emulsifier
ingredient and an inorganic electrolyte, together with an inorganic
sunblocking agent, namely ultrafine titanium dioxide.
DEFINITION OF THE INVENTION
Accordingly, the invention provides a water-in-silicone oil emulsion,
suitable for topical application to mammalian skin or hair, which
comprises, in addition to water;
i. from 1 to 50% by weight of a volatile polydimethylsiloxane,
ii. from 0.1 to 25% by weight of a silicone surfactant comprising a polymer
of dimethyl polysiloxane with polyoxyethylene and/or polyoxypropylene side
chains having a molecular weight of from 10,000 to 50,000 and having the
structure:
##STR1##
where the groups R' and R" are each chosen from --H, C.sub.1-18 alkyl and
##STR2##
a has a value of from 9 to 115, b has a value of from 0 to 50,
x has a value of from 133 to 673,
y has a value of from 25 to 0.25,
iii. from 0.1 to 10% by weight of a 2-hydroxyalkanoic acid having from 3 to
28 carbon atoms, or a salt, soap, acid-soap thereof, or mixtures thereof;
iv. from 1 to 10% by weight of ultrafine titanium dioxide having an average
particle size of from 1 to 100 nm; and
v. from 0.001 to 10% by weight of an inorganic electrolyte.
DISCLOSURE OF THE INVENTION
The emulsion of the invention is a water-in-silicone oil emulsion, which is
particularly suitable for topical application to mammalian skin or hair,
especially that of the human subject, for providing protection from the
damaging effects of sunlight. The emulsion is unusual in as much as it is
exceptionally stable and retains superior sensory attributes, with a high
degree of creaminess, both in terms of feel and appearance, yet without
undue whitening, this being due to the careful choice of both a
hydroxyalkanoic acid and an inorganic electrolyte, together with a
silicone emulsifier and volatile silicone.
The emulsion can also provide a vehicle for other skin and/or hair benefit
substances which can thereby be applied, with much greater ease and
control to the skin or hair at an appropriate concentration suited to
their intended benefit.
The Polydimethylsiloxane
The emulsion of the invention comprises a volatile polydimethylsiloxane
such as polydimethylcyclosiloxane having a viscosity of less than 5
mm.sup.2 s.sup.-1, examples of which are DOW CORNING 344 Fluid (tetramer)
and DOW CORNING 345 Fluid (pentamer), and volatile hexamethyldisiloxane
having a viscosity of not more than 0.65 mm.sup.2 s.sup.-1, for example
DOW CORNING 200 Fluid (0.65 mm.sup.2 s.sup.-1).
The preferred volatile siloxane is polydimethylcyclosiloxane (pentamer).
The emulsion will normally comprise from 1 to 50%, preferably from 5 to 20%
by weight of the volatile siloxane.
Silicone Surfactant
The emulsion of the invention also comprises a high molecular weight
silicone surfactant which acts as an emulsifier.
A preferred silicone surfactant is a high molecular weight polymer of
dimethyl polysiloxane with polyoxyethylene and/or polyoxypropylene side
chains having a molecular weight of from 10,000 to 50,000 and having the
structure:
##STR3##
where the groups R' and R" are each chosen from -H, C.sub.1-18 alkyl and
##STR4##
a has a value of from 9 to 115, b has a value of from 0 to 50,
x has a value of from I33 to 673,
y has a value of from 25 to 0.25.
Preferably, the dimethyl polysiloxane polymer is one in which:
a has a value of from 10 to 114
b has a value of from 0 to 49
x has a value of from 388 to 402
y has a value of from 15 to 0.75
one of groups R' and R" being lauryl, and the other having a molecular
weight of from 1,000 to 5,000.
A particularly preferred dimethyl polysiloxane polymer is one in which:
a has the value 14
x has the value 249
y has the value 1.25
The dimethyl polysiloxane polymer is conveniently provided as a dispersion
in a volatile siloxane, the dispersion comprising, for example, from 1 to
20% by volume of the polymer and from 80 to 99% by volume of the volatile
siloxane. Ideally, the dispersion consists of a 10% by volume of the
polymer dispersed in the volatile siloxane.
Examples of the volatile siloxanes in which the polysiloxane polymer can be
dispersed include those given above.
A particularly preferred silicone surfactant is cyclomethicone and
dimethicone copolyol, such as DC 3225C Formulation Aid available from DOW
CORNING. Another is laurylmethicone copolyol, such as DC Q2-5200, also
available from Dow Corning.
The emulsion according to the invention will normally comprise from 0.1 to
25%, preferably from 0.5 to I5% by weight of the silicone surfactant.
Non-volatile siloxane
The emulsion can also, optionally, comprise a non-volatile siloxane such as
a polydimethylsiloxane having a viscosity in excess of 5 mm.sup.2
s.sup.-1, for example, from 50 to 1,000 mm.sup.2 s.sup.-1, for example DOW
CORNING 200 Fluids (standard viscosities 50-1,000 mm.sup.2 s.sup.-1).
The Hydroxyalkanoic Acid
The emulsion of the invention also comprises a 2-hydroxyalkanoic acid
having from 3 to 28 carbon atoms.
Examples of hydroxyalkanoic acids include:
2-hydroxypropanoic acid
2-hydroxyhexanoic acid
2-hydroxyoctanoic acid
2-hydroxydecanoic acid
2-hydroxydodecanoic acid
2-hydroxytetradecanoic acid
2-hydroxyhexadecanoic acid
2-hydroxyoctadecanoic acid
2-hydroxyeicosanoic acid
2-hydroxydocosanoic acid
2-hydroxytetracosanoic acid
2-hydroxyhexacosanoic acid, and
2-hydroxyoctacosanoic acid
Particularly preferred hydroxyalkanoic acids are those having from 3 to 8
carbon atoms, especially
2-hydroxypropanoic acid, and
2-hydroxyoctanoic acid.
The 2-hydroxyalkanoic acids can also be present in the emulsion in the form
of their acid-soap complexes having from 6 to 56 carbon atoms, preferred
examples of which have an elemental analysis of:
(C.sub.m H.sub.2m-1/2 0.sub.3) (C.sub.n H.sub.2n-1/2 0.sub.3) M
where m and n have the same or different values, and each is an integer of
from 6 to 28, and M is a cation. The cation M is a monovalent ion such as
potassium, sodium, ammonium or a substituted ammonium.
A particularly preferred example of the acid-soap complex is that derived
from two molecules of 2-hydroxyoctanoic acid which has the empirical
formula C.sub.16 H.sub.31 O.sub.6 Na, as disclosed in EP A O 348 198.
The emulsion according to the invention will normally comprise from 0.1 to
10%, preferably from 0.5 to 5% by weight of the hydroxyalkanoic acid or
its acid-soap complex.
The Titanium Dioxide
The emulsion of the invention also comprises as a sunscreen material,
ultrafine titanium dioxide having an average particle size of from 1 to
100 nm, preferably from 10 to 40 nm, and most preferably from 15 to 25 nm.
Two forms of ultrafine titanium dioxide are available, either or both of
which can be employed in the emulsion of the invention, a
water-dispersible type and an oil-dispersible type.
Water-dispersible titanium dioxide in accordance with the invention is
ultrafine titanium dioxide, the particles of which are uncoated, or coated
With a material to impart a hydrophilic surface to the particles. Examples
of such materials include aluminium oxide and aluminium silicate.
Oil-dispersible titanium dioxide in accordance with the invention is finely
divided titanium dioxide, the particles of which exhibit a hydrophobic
surface, and which for this purpose can be coated with metal soaps, such
as aluminium stearate, aluminium laurate, zinc stearate, or with
organosilicone compounds.
The water-dispersible titanium dioxide, when present, has a greater
affinity with the aqueous phase of the emulsion, while the oil-dispersble
titanium dioxide, when present, has a greater affinity with the oily phase
of the emulsion.
The total amount of titanium dioxide in the emulsion according to the
invention is from I to 25%, preferably from 1 to 10% by weight of the
emulsion. Experimental evidence has shown that emulsions in accordance
with the invention which contain less than 1% by weight of ultrafine
titanium dioxide, provide little or no protection from excessive exposure
to sunlight, while similar emulsions which contain more than 25% by weight
of finely divided titanium dioxide do not further improve protection from
excessive exposure to sunlight beyond that obtainable when up to 25% of
the titanium dioxide is present. Furthermore, an excessive amount of
titanium dioxide in the emulsion according to the invention can leave the
skin white following topical application of the emulsion.
The protection afforded against the harmful effects of excessive exposure
to sunlight by sunscreen materials can be evaluated using an in vitro
technique which measures the Sun Protection Factor (SPF) of a sunscreen
material itself or a composition containing it (such as the emulsion
according to the invention). This technique, which is equally applicable
to inorganic sunscreen materials, such as ultrafine titanium dioxide, and
organic sunscreen materials, will be described later in this
specification.
The Inorganic Electrolyte
The emulsion of the invention also comprises an inorganic electrolyte which
serves to improve the stability of the emulsion, particularly when
subjected during storage to extremes of temperature.
Examples of inorganic electrolytes include salts, such as alkali metal and
ammonium halides, sulphates, nitrates, carbonates and bicarbonates in
either anhydrous or hydrated form.
Particularly preferred salts include sodium chloride, potassium chloride
and ammonium chloride.
The emulsion according to the invention will normally comprise from 0.1 to
10%, preferably from 0.2 to 5% by weight of an inorganic electrolyte.
Other Ingredients
The emulsion according to the invention can optionally comprise other
ingredients, further to enhance its properties and consumer appeal.
Organic Sunscreens
The emulsion of the invention optionally can comprise an organic sunscreen
further to enhance the benefit of the emulsion in providing protection
from the harmful effects of excessive exposure to sunlight.
As has already been stated, some organic sunscreens can be harmful to
health if applied topically to the skin at a concentration sufficient to
screen out effectively radiation from either the UV-A range or the UV-B
range. The presence however, of ultrafine titanium dioxide, which can
provide a broad spectrum of protection, enables a lower than usual amount
of organic sunscreen materials to be used to "top-up" the overall Sun
Protection Factor of the emulsion to an exceptionally high level, without
the risk of causing the type of skin damage or other health problems that
can be associated with the use of higher levels of organic sunscreen
materials alone.
In view of this, a relatively small amount of organic sunscreen optionally
can be incorporated into the emulsion of the invention.
Examples of suitable organic sunscreens, when required, include those set
out in Table 1 below, and mixtures thereof.
TABLE 1
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CTFA Name Trade Name Supplier
______________________________________
Benzophenone-3
UVINUL M-40 BASF Chemical Co.
Benzophenone-4
UVINUL MS-40 BASF Chemical Co.
Benzophenone-8
SPECRA-SORB American Cyanamide
UV-24
DEA
Methoxycinnamate
BERNEL HYDRO Bernel Chemical
Ethyl dihydroxy-
AMERSCREEN P Amerchol Corp.
propyl-PABA
Glyceryl PABA
NIPA G.M.P.A. Nipa Labs.
Homosalate KEMESTER HMS Humko Chemical
Methyl anthranilate
SUNAROME UVA Felton Worldwide
Octocrylene UVINUL N-539 BASF Chemical Co.
Octyl dimethyl
AMERSCOL Amerchol Corp.
PABA
Octyl methoxy-
PARSOL MCX Bernel Chemical
cinnamate
Octyl salicylate
SUNAROME Fleton Worldwide
WMO
PABA PABA National Starch
2-Phenyl- EUSOLEX 232 EM Industries
benzimidazole-
5-sulphonic acid
TEA salicylate
SUNAROME W Felton Worldwide
3-(4-methylbenzy-
EUSOLEX 6300 EM Industries
lidene)-camphor
Benzophenone-1
UVINUL 400 BASF Chemical Co.
Benzophenone-2
UVINUL D-50 BASF Chemical Co.
Benzophenone-6
UVINUL D-49 BASF Chemical Co.
Benzophenone-12
UVINUL 408 BASF Chemical Co.
4-Isopropyl EUSOLEX 8020 EM Industries
dibenzoyl methane
Butyl methoxy di-
PARSOL 1789 Givaudan Corp.
benzoyl methane
Etocrylene UVINUL N-35 BASF Chemical Co.
______________________________________
The emulsion of the invention can accordingly comprise from 0.1% to 10%,
preferably from 1 to 5% by weight of an organic sunscreen material.
Other Inorganic Sunscreens
The emulsion of the invention optionally can comprise an inorganic
sunscreen in addition to ultrafine titanium dioxide as herein defined.
Examples of other inorganic sunscreens include:
zinc oxide, having an average particle size of from 1 to 300 nm,
iron oxide, having an average particle size of from 1 to 300 nm,
silica, such as fumed silica, having an average particle size of from 1 to
100 nm.
It should be noted that silica, when used as an ingredient in the emulsion
according to the invention can provide protection from infra-red
radiation.
The emulsion of the invention can accordingly comprise up to 20%,
preferably from 1 to 10% by weight of other inorganic sunscreens.
Alkane Diol
The emulsion of the invention optionally can also comprise an alkane diol,
or a mixture thereof, which can serve further to improve and prolong the
stability of the emulsion, particularly when a very long period of
storage, for example of at least 12 months or even up to 3 years, is
anticipated.
The preferred alkane diols for this purpose when used are those having from
2 to 10 carbon atoms in the molecule. Examples of particularly preferred
alkane diols are:
ethane diol
propane-1,2-diol
propane-1,3-diol
butane-1,3-diol
butane-1,4-diol
butane-2,3-diol
pentane-1,5-diol
hexane-1,6-diol
octane-1,8-diol, and
decane-1,10-diol
An especially preferred alkane diol is butane-1,3-diol.
The emulsion according to the invention can comprise up to 30%, most
preferably from 1 to 25% by weight of an alkane diol.
Cosmetically Acceptable Vehicle
The emulsion of the invention optionally can comprise a cosmetically
acceptable vehicle, in addition to water, to act as a dilutant, dispersant
or carrier for other materials present in the emulsion, so as to
facilitate their distribution when the emulsion is applied to the skin
and/or hair.
Vehicles other than water can include liquid or solid emollients, solvents,
humectants, thickeners and powders. Examples of each of these types of
vehicle, which can be used singly or as mixtures of one or more vehicles,
are as follows:
Emollients, such as stearyl alcohol, glyceryl monoricinoleate, mink oil,
cetyl alcohol, isopropyl isostearate, stearic acid, isobutyl palmitate,
isocetyl stearate, oleyl alcohol, isopropyl laurate, hexyl laurate, decyl
oleate, octadecan-2-ol, isocetyl alcohol, eicosanyl alcohol, behenyl
alcohol, cetyl palmitate, di-n-butyl sebacate, isopropyl myristate,
isopropyl palmitate, isopropyl stearate, butyl stearate, lanolin, cocoa
butter, corn oil, cotton seed oil, olive oil, palm kernel oil, rapeseed
oil, safflower seed oil, jojoba oil, evening primrose oil, soybean oil,
sunflower seed oil, avocado oil, sesame seed oil, coconut oil, arachis
oil, castor oil, acetylated lanolin alcohols, petroleum jelly, mineral
oil, butyl myristate, isostearic acid, palmitic acid, isopropyl linoleate,
lauryl lactate, myristyl lactate, decyl oleate, myristyl myristate;
Propellants, such as propane, butane, isobutane, dimethyl ether, carbon
dioxide, nitrous oxide;
Solvents, such as ethyl alcohol, methylene chloride, isopropanol, acetone,
ethylene glycol monoethyl ether, diethylene glycol monobutyl ether,
diethylene glycol monoethyl ether, dimethyl sulphoxide, dimethyl
formamide, tetrahydrofuran;
Powders, such as chalk, talc, fullers earth, kaolin, starch, gums,
colloidal silica sodium polyacrylate, tetra alkyl and/or trialkyl aryl
ammonium smectites, chemically modified magnesium aluminium silicate,
organically modified montmorillonite clay, hydrated aluminium silicate,
fumed silica, carboxyvinyl polymer, sodium carboxymethyl cellulose,
ethylene glycol monostearate, pigmentary titanium dioxide, titanium
dioxide-coated mica.
The cosmetically acceptable vehicle, when present, will usually form up to
to 99.9%, preferably from 10 to 99% by weight of the emulsion, and can, in
the absence of other cosmetic adjuncts, form the balance of the emulsion.
Cosmetic Adjuncts
Examples of conventional adjuncts which can optionally be employed include
preservatives, such as para-hydroxy benzoate esters; antioxidants, such as
butyl hydroxy toluene; solvents, such as ethyl alcohol and isopropanol;
humectants, such as glycerol, sorbitol, 2-pyrrolidone-5-carboxylate,
dibutylphthalate, gelatin, polyethylene glycol, preferably PEG 200-600;
buffers, such as lactic acid together with a base such as triethanolamine
or sodium hydroxide; amino acids such as L-proline waxes, such as beeswax,
ozokerite wax, paraffin wax; plant extracts, such as Aloe vera,
cornflower, witch hazel, elderflower, cucumber; thickeners; other skin
benefit ingredients, such as hyaluronic acid or the sodium salt thereof;
activity enhancers; colourants; and perfumes. Cosmetic adjuncts can form
up to 50% by weight of the emulsion and can conveniently form the balance
of the emulsion.
It is to be explained that the incorporation of L-proline as a cosmetic
adjunct into the composition according to the invention is particularly
advantageous, as this amino acid is believed to rebuild collagen, a
proline-rich protein which is an important structure in skin.
pH
The aqueous phase of the emulsion according to the invention should
preferably have a pH value of from 3.5 to <7.
Process for Preparing the Emulsion
The invention also provides a process for the preparation of an emulsion
for topical application to skin and/or hair which comprises the step of
incorporating into the emulsion a volatile polydimethylsiloxane, a
silicone surfactant, a 2-hydroxyalkanoic acid, an inorganic electrolyte
and an inorganic sunscreen as herein defined.
Use of the Emulsion
The emulsion according to the invention is intended primarily as a product
for topical application to human skin, particularly dry skin, when
repeated application can alleviate the dry condition and restore the skin
to a more natural, soft, supple, healthy state. The emulsion is also
useful for protecting exposed skin from the harmful effects of excessive
exposure to sunlight. The emulsion can also be used to treat the hair and
the scalp.
In use, a small quantity of the emulsion, for example from 1 to 5 ml, is
applied to the affected area of skin or hair, or to exposed areas of skin,
from a suitable container or applicator and, if necessary, it is then
spread over and/or rubbed into the skin or hair using the hand or fingers
or a suitable device.
Product Form and Packaging
The topical skin and/or hair treatment emulsion of the invention can be
formulated as a lotion having a viscosity of from 4,000 to 10,000 mPas, a
fluid cream having a viscosity of from 10,000 to 20,000 mPas or a cream
having a viscosity of from 20,000 to 100,000 mPas, or above. The emulsion
can be packaged in a suitable container to suit its viscosity and intended
use by the consumer. For example a lotion or a fluid cream can be packaged
in a bottle or a roll-ball applicator or a propellant-driven aerosol
device or a container fitted with a pump suitable for finger operation.
When the emulsion is a cream, it can simply be stored in a non-deformable
bottle or squeeze container, such as a tube or a lidded jar.
The invention accordingly also provides a closed container containing a
cosmetically acceptable emulsion as herein defined.
Method for determination of Sun Protection Factor (SPF) in vitro
The method for the in vitro SPF determination of the emulsion of the
invention involves the spectrophotometric scanning of stratum corneum
between 400 nm and 290 nm utilising a Perkin Elmer Lamba 17
spectrophotometer equipped with a diffuse transmission detection system.
Guinea pig stratum corneum is used in place of human skin and the following
procedure is followed.
i. Guinea pig stratum corneum is isolated as fine sheets from guinea pig
skin and air dried.
ii. A piece of the stratum corneum is applied to the outer surface of a 0.5
cm quartz cuvette using a drop of distilled water to seal the stratum
corneum uniformly to the quartz surface.
iii. The quartz cuvette carrying the piece of stratum corneum is placed in
the light path of the spectrophotometer which for this purpose is fitted
with a fluorescence cut-off filter. This filter eliminates the
autofluorescence of the stratum corneum and filters out all transmissions
above 400 nm.
iv. The stratum corneum is scanned from 290 to 400 nm and the spectrum
obtained is saved as the control.
v. The cuvette with stratum corneum is removed from the spectrophotometer
and the test material (i.e. sunscreen) is applied to the stratum corneum
at the rate of 1.5 .mu.l/cm.sup.2, in accordance with German DIN protocol,
and rubbed uniformly across the entire surface of the skin using the
finger fitted with a finger stall.
vi. The applied sunscreen material is allowed to stand for 5 minutes at
room temperature (20.degree. C.) to enable it to dry, and then the sample
is rescanned in the spectrophotometer as before from 290 to 400 nm. This
spectrum is saved as the test spectrum. No spectral absorbance changes
were observed with drying times between 2 and 15 minutes; the 5 minute
drying time was therefore adopted as standard.
vii. The control spectrum is subtracted from the test spectrum to provide
the spectral absorbance of the test sample of sunscreen material and this
absorbance is converted to transmission.
viii. The in vitro Sun Protection Factor (SPF) is finally calculated from
transmission measurements as described by Diffey et al in a paper
entitled: "A new substrate to measure sunscreen factors throughout the
ultraviolet spectrum" in J.Soc. Cosmet. Chem. 40, 127-133 (May/June 1989):
see especially page 130.
EXAMPLES
The invention is further illustrated by the following examples.
EXAMPLE 1
This example illustrates a lotion according to the invention.
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