Skincare compositions
This invention relates to compositions for use in skincare, in particular to compositions intended to have a moisturising effect when applied topically to the skin.
A wide variety of compositions are commonly applied directly to the skin. These include compositions intended to have a therapeutic effect upon the skin, as well as cosmetic compositions that are intended to modify the appearance of the skin.
Many compositions suited to the type and/or age of the skin are applied to the skin with the aim of maintaining the skin in a smooth and supple condition. Dry skin is characterised by a lack of moisture caused on the one hand by increased water loss and on the other hand by reduced water-holding capacity. These effects may come about as a result of exposure of the skin to, for instance, conditions of low humidity, to wind, or such effects may be due to genetic predisposition. The balance of water loss and water-holding capacity may also be disturbed by prolonged exposure to surfactants, which promote dissolution of lipids in the skin that otherwise help to retain moisture in the stratum corneum act as a water loss shield.
One important benefit that is commonly sought from compositions applied topically to the skin is therefore moisturisation, ie the maintenance or elevation of the level of hydration of the skin. Improved moisturisation may prevent or inhibit the occurrence of dry and flaky skin, and may improve the elasticity and smoothness of the skin. Many products are used solely for their moisturising properties, eg as "Day Creams" that are intended to be applied and worn throughout the day. Similarly, "Night Creams" are applied before the user retires for the night and are worn throughout the hours of sleep.
A disadvantage of known compositions that are intended to have a moisturising effect on the skin is that the effect may be less than would otherwise be desired,
and more particularly may be less long-lasting than would be desired. Thus, while application of the composition to the skin may initially give rise to a benefit, that benefit may not be as great as would be desired, may not persist for as long as would be desired, and/or may not be as constant as would be desired. For instance, it is commonly found that moisturisation increases over the course of about two hours, but then falls. Where the moisturisation effect is longer lasting, the degree of moisturisation may vary considerably with time, whereas a more uniform, more substantially constant effect would be preferable.
It is clearly desirable that compositions of this type should not have to be frequently reapplied in order for the benefit to be maintained. For most users, it is possible or convenient to apply the composition only once or twice each day. in the case of a "day cream" this might typically be in the morning and then perhaps in the early evening. There is therefore a need for a skincare composition that exerts a moisturising effect that persists for prolonged periods, and in particular for compositions that exert a moisturising effect on the skin that lasts sufficiently long for the effect to be maintained by application of the composition no more frequently than four times per day, and ideally only once or twice per day.
A material known as "Advanced Moisture Complex" is available from Engelhard Corporation and comprises a complex of six different moisturising agents, viz glycerin, sodium PCA, urea, trehalose, Polyquaterniurn-51 and sodium hyaluronate. In a document identified by the BNSDOCID accession number XP2339058A it is stated that each of these components is a performance ingredient in its own right, yet none of them alone provide sustained long-term moisturisation. The same document discloses a cream formulation comprising 10% Advanced Moisture Complex and 2.1 % of a phosphate modified corn starch derivative known as "Structure Zea". Structure Zea is described in a document identified by the BNSDOClD accession number XP-002339059 issued by National Starch & Chemical, where it is described as a rheology and aesthetics modifier for dilutable powders and emulsion products.
US-A-2003/0215471 discloses a number of compositions comprising Structure Zea as a rheology modifying agent and Advanced Moisture Complex.
It has now surprisingly been found that improved moisturisation properties can be achieved by incorporation into a composition for topical application to the skin of a dimethyl imidazolidinone starch derivative and a polymeric quaternary ammonium salt having humectant properties, and there have hence now been devised improved skincare compositions that exhibit improved, and in particular more long- lasting, and/or more constant, moisturisation effects on the skin. Whilst the composition may comprise one or more additional moisturising agents, the moisturising effect, and in particular the prolonged moisturisation effect, does not depend on the presence of a large number of complementary moisturising agents. Thus, according to a first aspect of the invention, there is provided a composition for topical application to the skin, which composition comprises a starch or starch derivative and a polymeric quaternary ammonium salt having humectant properties, provided that when the starch or starch derivative is a corn starch derivative and the polymeric quaternary ammonium salt is polyquaternium-51 , then the composition does not also comprise glycerin, sodium PCA, urea, trehalose and sodium hyaluronate.
The composition according to the invention is advantageous primarily in that it exerts a significant moisturisation effect on the skin, and moreover that effect persists for an extended period. As a consequence, enhanced and persistent moisturisation of the skin may be achieved by only a small number of applications of the composition each day, perhaps as infrequently as once or twice per day. Moreover, the moisturisation effect may be more constant than effects achieved with other moisturising compositions, which may in turn lead to improved compliance as the skin may not be subject to substantial rises and falls in moisturisation that might influence the frequency of application of the composition.
The starch or starch derivative is preferably a chemically or physically modified starch. Most preferably, the starch is modified so as to render it heat-stable and/or non-sweiling.
A preferred form of starch derivative is a dimethyl imidazolidinone starch derivative, ie a product obtained by reaction of 1 ,3-dimethy[-4,5-dihydroxy-2- imidazolidinone (dimethyl imidazolidinone) with starch. Particular starches that may be used include corn starch but, more preferably, the starch is rice starch. The dimethyl imidazolidinone starch derivative may thus be dimethyiimidazolidinone corn starch or, more preferably, dimethylimidazolidinone rice starch.
A suitable form of dimethylimidazolidinone rice starch is available from Agrana u. Staerke AG, Conrathstr. 7, A-3950 Gmuend, Austria, under the trade name Rice NS. Another supplier is Dr Hauser, Reintalstrasse 8, D-82467 Garmisch- Partenkirchen, Germany.
The starch or starch derivative is preferably present in the composition according to the invention at a level of less than 15% w/w, preferably less than 10% w/w, and more preferably less than 5% w/w. The concentration of starch derivative is preferably greater than 0.1% w/w, and more preferably greater than 1% w/w. The concentration of starch derivative is therefore preferably in the range 0.1 % to 15% w/w, and more preferably in the range 1 % to 5% w/w, particularly 2.25% to 3.75% w/w.
The polymeric quaternary ammonium salt is most preferably the material known as Polyquaternium-51 , ie the polymeric quaternary ammonium salt that conforms generally to the formula:
A suitable form of polyquaternium-51 is available from NOF Corporation, 4-20-3, Ebisu, Shibuya-ku, Tokyo 150, Japan, under the trade name Lipidure-PMB.
The ammonium salt is preferably present in the composition according to the invention at a level of less than 1% w/w, more preferably less than 0.1% w/w. The concentration of ammonium salt is preferably greater than 0.0001 % w/w, and more preferably greater than 0.001 % w/w. The concentration of ammonium salt is therefore preferably in the range 0.0001 % to 1 % w/w, and more preferably in the range 0.001% to 0.1% w/w.
The composition according to the invention may comprise one or more additional moisturising or humectant ingredients, ie moisturising or humectant ingredients that are additional to the starch derivative and the ammonium salt.
Most preferably, the additional moisturising or humectant ingredient is a relatively low molecular weight polyalcohol, eg a C2-6 aliphatic polyalcoho!. Examples of such poiyalcohols include glycerin (1 ,2,3-trihydroxypropane), 1 ,3-butylene glycol and propylene glycol. The most preferred additional moisturising or humectant ingredient is glycerin.
The additional moisturising or humectant ingredient(s) are preferably present in the composition at a level of up to 25% w/w or more, more preferably up to 20% w/w. The concentration of additional moisturising or humectant ingredient(s) is preferably greater than 1 % w/w, more preferably greater than 5% w/w, and most preferably greater than 10% w/w. The concentration of additional moisturising or humectant ingredient(s) is therefore preferably in the range 1% to 25% w/w, and more preferably in the range 5% to 20% w/w.
Where glycerin is present in the composition, the concentration of glycerin is preferably in the range 1 % to 20% w/w, more preferably in the range 10% to 20% w/w, and in particular in the range 10% to 15% w/w.
The composition may comprise more than one aliphatic polyalcohol. In some embodiments, the composition comprises both glycerin and propylene glycol.
Compositions comprising one or more aliphatic polyalcohols have been found to be particularly beneficial. In a more specific aspect, the invention thus provides a composition for topical application to the skin, which composition comprises a starch or starch derivative, a polymeric quaternary ammonium salt having humectant properties, and from 10% to 20% w/w of one or more aliphatic polyalcohols. The polyalcohols are preferably C2-e aliphatic polyalcohols, most preferably selected from the group consisting of glycerin (1 ,2,3-trihydroxypropane), 1 ,3-butylene glycol and propylene glycol. Preferably, the composition comprises glycerin.
In preferred embodiments, the composition is free of any additional moisturising agents other than the low molecular weight polyalcohols. In particular, the composition is preferably free of sodium PCA, urea, trehalose and sodium hyaluronate.
Compositions in accordance with the invention may be formulated in any one of numerous different forms. Suitable types of composition, and methods by which they may be prepared, will generally be evident to those skilled in the art.
One preferred group of compositions are formulated as emulsions. The emulsions may be o/w, w/o, o/w/o or w/o/w emulsions. Preferred emulsion compositions are o/w emulsions. Such emulsion-type compositions may be described inter alia as creams or lotions. Other emulsion compositions are w/o emulsions. Another preferred group of compositions are formulated as gels.
As moisturisation of the skin is an important benefit of the compositions according to the invention, additional ingredients that contribute to improved skin-feel are preferably present. Such additional ingredients may include skin conditioning agents, as well as thickeners, particularly thickeners for the aqueous phase of emulsion compositions.
Suitable skin conditioning agents that may be present include ingredients having emollient properties, ie ingredients which help to maintain the soft, smooth and pliable appearance of the skin, and which function by their ability to remain on the skin surface or in the stratum corneum to act as lubricants, to reduce flaking and to improve the skin's appearance. Suitable skin conditioning ingredients will be evident to those skilled in the art, but examples include PPG-15 stearyl ether, ethylhexyl stearate, cetyl dimethicone, octyldodecanoi, PPG-20 methyl glucose ether, isopropyl myristate isopropyl palmitate, isopropyl laurate isodecy! laurate, isodecyl neopentanoate, isohexadecane, pentaerythrityl tetraisostearate, caprylic/capric triglyceride, canola oil, sunflower oil (Heiianthus annuus), olive oil (Olea europea), cottonseed oil (Gossypium herbaceum), jojoba oil (Simmondsia chinensis), shea butter (Butyrospermum parkii), cocoa butter {Theobroma cacao), cupuacu butter (Theobroma grandiflorum), avocado oil {Persea gratissima), evening primrose oil (Oenothera biennis), mineral oil, liquid paraffin, squalane, dimethicone, phenyl trimethicone, cyciomethicone, cyclopentasiloxane, dimethicono! and petrolatum.
Suitable thickeners will also be evident to those skilled in the art, but examples include hydrophiiic polymers and derivatives thereof, eg agarose, carbomer, polyacrylamide, alkyl acrylate crosspolymer, carboxymethyl hydroxyethylceliulose, hydroxyethyl cellulose, xanthan gum, cellulose gum, and hydroxypropyl starch.
The composition will generally also comprise other ingredients or excipients which constitute or form part of a dermatologically acceptable carrier and will be well known to those skilled in the art. These include, for example:
a) Surfactants - anionic surfactants, eg sodium lauryl sulphate, sodium laureth sulphate, ammonium laureth sulphate, disodium laureth suifosuccinate and sodium C12-15 pareth sulphate; amphoteric/zwitterionic surfactants, eg coca mido propyl betaine, sodium cocoa mphoacetate and cocamidopropyl hydroxysultaine; nonionic surfactants, eg laureth-3, oleth-5, cocamide DEA, cocamide MEA, PEG-5 cocamide, sucrose cocoate, polysorbate 20, PEG- 40 hydrogenated castor oil; and cationic surfactants, eg cetrimonium chloride, behentrimonium chloride and benzalkonium chloride.
b) Emulsifiers, eg steareth-2, steareth-21 , steareth-10, ceteareth-5, ceteareth- 12, ceteareth-20, oleth-10, glyceryl stearate, polyglyceryi-3 oleate, polyglyceryl-3 methylglucose distearate, sodium cetearyl sulphate, sodium stearate, PEG-12 Oleate, PEG-2 stearate, PEG-12 stearate, PEG-80 sorbitan, sorbitan oleate, sorbitan palmitate, sorbitan stearate and cetyl PEG/PPG-10/1 dimethicone.
c) Chelating agents or sequestering agents (sequestrants) - ingredients that have the ability to complex with and inactivate metallic ions in order to prevent their adverse effects on the stability or appearance of the composition. Examples of chelating agents are ethylenediamine tetraacetic acid and its salts, notably the dipotassium and especially the disodium or tetrasodium salt.
d) Sunscreening agents - inorganic sunscreening agents, eg microfine titanium dioxide, microfine zinc oxide, iron oxides, talcs and boron nitride; and/or organic sunscreening agents, eg p-aminobenzoic acids, esters and derivatives thereof, for example, 2-ethylhexyl p-dimethylaminobenzoate and the octyl ester of p-aminobenzoic acid; methoxycinnamate esters such as 2-ethylhexyi p-methoxycinnamate, 2-ethoxyethyl p-methoxycinnamate or α,β-di-(p-methoxycinnamoyl)-α'-(2-ethylhexanoyl)-glycerin; benzophenones such as oxybenzone; 2-phenylbenzimidazole-5-suifonic acid and disodium phenyl dibenzimidazole tetrasulfonate and terphthalylidene dicamphor sulfonic acid; alkyl-β,β-diphenylacrylates for example alkyl α-cyano-β,β- diphenylacryiates such as octocrylene; triazines such as 2,4,6-trianilino-(p- carbo-2-ethylhexyl-1'-oxy)-1 ,3,5 triazine and bis-octyloxyphenoi methoxyphenyl triazine; camphor derivatives such as methyibenzyiidene camphor; organic pigment sunscreening agents such as methylene bis- benzothazole tetramethyl butylphenol; silicone derivatives such as drometrizoie trisiloxane, benzylidene malonate polysiloxane and dimethicodiethyl benzal malonate, salicylates such as octyl salicylate.
e) Preservatives - ingredients which prevent or retard microbial growth and thus protect the composition from spoilage. Examples of preservatives include DMDM hydantoin, propylparaben, methylparaben, phenoxyethanol, sodium benzoate, bronopol, sodium dehydroacetate, polyhexamethylenebiguanide hydrochloride, isothiazolone and diazolidinylurea.
f) Perfumes and colourings.
g) pH adjusting agents.
As described above, the compositions according to the invention are useful in that they enhance the moisturisation of the skin. Thus, according to a further aspect of
the invention, there is provided a method for moisturising skin, which method comprises the topical application to the skin of a composition comprising a dimethyl imidazolidinone starch derivative and a polymeric quaternary ammonium salt having humectant properties, provided that when the starch or starch derivative is a corn starch derivative and the polymeric quaternary ammonium salt is polyquaternium-51 , then the composition does not also comprise glycerin, sodium PCA, urea, trehalose and sodium hyaluronate.
The skin to which the composition is applied will most commonly be human skin, • the composition generally being applied by the user to his or her own skin.
Usually, the composition will be applied to areas of skin that are normally exposed, eg the face and/or neck, the arms, hands or legs.
A presently preferred embodiment of the invention will now be described, by way of illustration only, with reference to the following Examples.
Example 1
Body Cream (oil-free)
Inqredients: % w/w
Phase I :
Dimethicone/Dimethiconol 3.000
Polyacrylamide/C12-14 lsoparaffin/Laureth-7 2.000
Phase II:
Aqua 76.600
Dimethyϋmidazolidinone Rice Starch 2.500
Glycerin 12.000
Phenoxyethanol 1.000
Phase III:
Parfum 0.200
Aqua/Polyquaternium-51 /Phenoxyethanol 0.200
Aluminum Starch Octenylsuccinate 2.500
Method:
Heat Phase I and Phase Il to 600C. Homogenize and cool to 200C.
Add Phase III.
Example 2
Bodv Lotion W/O
Ingredients: % w/w
Phase I :
Cyclomethicone 11.000 lsopropylmyristate 7.000
Isohexadecane 4.000
Cetyl Dimethicone 5.000
Bis-PEG/PPG-14/14 Dimethicone 3.000
Phase II:
Aqua 52.100
Dimethylimidazolidinone Rice Starch 2.500
Glycerin 12.000
Phenoxyethanol 1.000
Sodium Chloride 2.000
Phase III:
Parfum 0.200
Aqua/Polyquaternium-51 /Phenoxyethanol 0.200
Method:
Heat Phase I and Phase Il to 60°C
Homogenize and cool to 2O0C. Add Phase III,
Example 3
Bodv Lotion O/W
Ingredients: % w/w
Phase I :
Cyclomethicone 11.000 lsopropylmyristate 7.000
Isohexadecane 4.000
Cetearyl Alcohol 0.500
Cetearyl Giucoside 0.500
Acrylates/C10-30 Alkyl Acrylates 0.150 Crosspolymer
Phase II:
Aqua 60.950
Dimethylimidazolidinone Rice Starch 2.500
Glycerin 12.000
Phenoxyethanol 1.000
Phase ill:
Parfum 0.200
Aqua/Polyquaternium-51/Phenoxyethanol 0,200
Method:
Heat Phase I and Phase Il to 600C. Homogenize and cool to 2O0C.
Add Phase III.
Example 4
Dav Cream
Ingredients: % w/w
Phase !:
Aqua 50.826
Glycerin 12.002
Sorbitan Stearate 5.087
Sucrose Cocoate 0.413
Dimethylimidazolidinone Rice Starch 2.500
Disodium EDTA 0.050
Xanthan Gum 0.100
Phase II:
Caprylic/Capric Triglyceride 5.000
Isohexadecane 5.000
Mineral Oil 5.000
Squalane 1.500
Butyrospermum parkii 1.000
Cetearyl Alcohol 1.000
Phase III:
Cyclomethicone 2.000
Carbomer 0.120
Phase IV:
Propylene Glycol 4.000
Aluminum Starch Octenylsuccinate 3.000
Phase V:
Polyquaternium-51 0.010
Tocopherol 0.100
Phenoxyethanol 1.000
Parfum 0.250
Phase Vl:
Sodium Hydroxide 0.042
Method:
Heat phase I and Il separately to 8O0C and keep phase I on temperature for 20 min.
Add phase I to Il and homogenize. At 600C, add the premix of phase III.
At 400C, add phase IV and at room temperature mix phase V to the formulation. Finally, adjust the viscosity with phase Vl.
Demonstration of Moisturisation Effects
The moisturisation effects of the above Day Cream (Example 4) were demonstrated as follows:
1. Short-term kinetic (24 hour) study
The objective of this study was the evaluation of alterations of skin hydration by the Day Cream after 24 hours, in comparison with untreated skin.
Method
The study was conducted double blind on 30 female volunteers. The subjects were aged between 20.5 and 65.4 years.
The baseline values (units of the Corneometer CM 825) of the investigation sites were lower than 40 in the mean. Before the start of the measurements and treatments there was a preconditioning period of 7 days. The analysis of the skin care product in comparison to an untreated investigation site was performed at both volar forearms. Product was applied to the site once at a quantity of 2μl/cm2. The hydration was measured immediately before starting the product application (t0), and at 2 hours Ct1), 4 hours (t2), 6 hours (t3), 8 hours (t4), 12 hours
(t5) and 24 hours (t6) after the treatment. The measurements were performed in a climate controlled room at 21.50C (+/-10C) and 50% (+/- 5%) relative humidity after the volunteers had adapted themselves to these indoor climate conditions for 30min.
Results
The measured percentage increase in moisturisation relative to baseline is shown as a function of time in Figure 1. The Day Cream induced a clear, statistically significant increase in the moisture of the skin during the whole measurement period (24h) after a single application. The skin hydration increased until the measurement after 6 hours, peaking at a moisturisation level greater than 40%. Furthermore, there was no significant difference between the 4 and 8 hour values, and even the 12 hour value was higher than the 2 hour value. Thus, the moisturisation level was nearly stable over 12 hours with a peak at 6 hours. Even after 24 hours the moisturisation level after single application was more than 20% above baseline.
2. One week skin care study
The objective of the skin care study was the evaluation of alterations in the skin hydration of one product after a one week treatment regimen compared to untreated skin.
Method:
The study was conducted double blind on 33 female volunteers. The subjects were aged between 27.2 and 55.5 years.
The baseline values (units of the Corneometer CM 825) of the investigation sites were lower than 40 in the mean. Before the start of the measurements and treatments there was a preconditioning period of 7 days. The analysis of the skin care product in comparison to an untreated investigation site was performed at both volar forearms. Skin hydration was measured immediately before starting the product application (t0). After measurement time point to the Day Cream was applied to one volar forearm in normal quantities by the volunteers themselves, twice daily over a period of one week. The measurements were performed in a climate controlled room at 21.5°C (+/-1°C) and 50% (+/- 5%) relative humidity after the volunteers had adapted themselves to these indoor climate conditions for 30min.
Result:
The day cream induced a statistically significant increase in the moisturisation of the skin of about 39% after seven days application.