Cosmetic Product Stability

7/22/2019 Cosmetic Product Stability

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Product StabilityProduct StabilityWhat is it?What is it?

How do we test it?How do we test it?

How can we improve it?How can we improve it?


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John Woodruff; Creative Developments(Cosmetics) Ltd.4

Definition of StabilityDefinition of Stability

In mathematics, stability theory addresses theIn mathematics, stability theory addresses the

stability of solutions of differential equations andstability of solutions of differential equations and

of trajectories of dynamical systems under smallof trajectories of dynamical systems under small

perturbations of initial conditions.perturbations of initial conditions.

In probability theory, the stability of a randomIn probability theory, the stability of a random

variable is the property that a linear combinationvariable is the property that a linear combination

of two independent copies of the variable hasof two independent copies of the variable has

the same distribution, up to location and scalethe same distribution, up to location and scale

parameters. ...parameters. ...


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-- the quality of being enduring and freethe quality of being enduring and free

from change or variationfrom change or variation

-- resistant to change of position orresistant to change of position or

conditioncondition -- firm and dependable; subject to littlefirm and dependable; subject to little

fluctuationfluctuation

-- not taking part readily in chemicalnot taking part readily in chemicalchangechange


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What do we understand about it with regard toWhat do we understand about it with regard to

cosmetic products?cosmetic products?

That a product remainThat a product remainfit for purposefit for purpose

AppearanceAppearance Purity including lack of microbial contaminationPurity including lack of microbial contamination

EfficacyEfficacy

That it remains fit for purpose for a period of notThat it remains fit for purpose for a period of not

less than 36 months from manufacture and notless than 36 months from manufacture and not

less than its PAO declarationless than its PAO declaration


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Examples of InstabilityExamples of Instability


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ObviousObvious

Emulsion breakdownEmulsion breakdown

Perfume changesPerfume changes

Colour changesColour changes Viscosity changesViscosity changes

Fungal growthFungal growth

Wax crystallisationWax crystallisation

Sediment in clear lotionsSediment in clear lotions


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Less ObviousLess Obvious

pH changespH changes

Loss of activityLoss of activity

VitaminsVitaminsAntioxidantsAntioxidants

EnzymesEnzymes

PreservativesPreservatives

PhotoPhoto--degradation of UV filtersdegradation of UV filters Microbial growthMicrobial growth


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Emulsion CreamingEmulsion Creaming


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4 days at room temperature 1 month at 45C1 month at room temperature

4 days at room temperature 1 month at room temperature

1 month at 45C

Emulsion BreakdownEmulsion Breakdown


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Viscosity ChangesViscosity Changes

0

10

20

30

40

50

60

70

Initial 5 days 10 15 20 25 30 days

Increasing Decreasing Stable


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Worst Nightmare!Worst Nightmare!

Atmospheric Mould Colonies


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Crystal GrowthCrystal Growth


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Testing for StabilityTesting for Stability

Prepare a pilot batch and store it in itsPrepare a pilot batch and store it in its

retail packaging and check that it remainsretail packaging and check that it remains

fit for purpose for a period of not less thanfit for purpose for a period of not less than

36 months from manufacture and not less36 months from manufacture and not lessthan its PAO declaration!than its PAO declaration!

ImpracticalImpractical

What other options?What other options?


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Testing SchedulesTesting Schedules

Examples of suitable schedules are givenExamples of suitable schedules are given

in the IFSCC Monographin the IFSCC Monograph

Boots publishes a scheme that itsBoots publishes a scheme that itssuppliers are expected to usesuppliers are expected to use --GR10GR10

Distance Learning Course (DLC) includesDistance Learning Course (DLC) includes

suggestions in its module on stabilitysuggestions in its module on stability


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IFSCC MonographIFSCC Monograph

4400 ambient humidityambient humidity -- retain as controlretain as control

202000 / 25/ 2500 ambient humidityambient humidity -- 60 months60 months

373700 ambient humidityambient humidity -- 6 months6 months

454500 ambient humidityambient humidity -- 3 months3 months

373700 &&80% relative humidity80% relative humidity -- 1 month1 month

Freeze / ThawFreeze / Thaw Light exposureLight exposure


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DLC RecommendationsDLC Recommendations


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DLC RecommendationsDLC Recommendations

1 month assessment (all storage conditions)





1 year assessment (all storage conditions)

18 month assessment (5C and RT storage conditions only)

2 year assessment (5C and RT storage conditions only)

30 month assessment (5C and RT only)

3 year assessment (5C and RT storage conditions only).


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Boots recommendation - Stability and final pack compatibility of all cosmeticand toiletry products should be assessed to establish that they are stableand that no separation, crystallisation, contamination, degradation or otherinstability occurs within the claimed product shelf life

40C0C to 30CProducts sold in tropical

climates

30C0C to 23CProducts sold in temperate

climates

Must be safe to use,

effective

and stable in final packfor at least 3 months at:

Must be safe to use,

effective

and stable in final packfor at least 36 months at:

Stability Requirements

Product must also be safe to use within their specified Period After Opening (PAO),

no matter at what point in their shelf life they are first opened.


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What should be checked?What should be checked?


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What is ImportantWhat is Important

Consider thefunctionof the product under test anddecide whether or not the changes observed could affectthis

Consider thesafetyof the product under test and decidewhether or not the changes observed could affect this

Consider whether the changes observed affect theaestheticsof the product under test

Note under what storage conditions any changesobserved take place and try to relate these to theenvironment in which the product is to be sold

Look for significant trends in changes of productattributes


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Talking PointsTalking Points

What is important for this product in thisWhat is important for this product in this

packaging for this market?packaging for this market?

Setting product specificationSetting product specification

Minimum and maximum for each parameterMinimum and maximum for each parameterWhy these numbers?Why these numbers?

Have products been prepared and tested atHave products been prepared and tested at

extreme specification limits?extreme specification limits?

Release specifications / shelfRelease specifications / shelf--life specificationslife specificationsWhat matters?What matters?


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Accelerated Testing for StabilityAccelerated Testing for Stability

Prepare a pilot batch and store it in its retailPrepare a pilot batch and store it in its retail

packaging:packaging:--

Room Temperature (RT) for 24 monthsRoom Temperature (RT) for 24 months

44C for 3 monthsC for 3 months 4040C for 3 monthsC for 3 months

44C/40C/40C Cycle for a number of cyclesC Cycle for a number of cycles

In a NIn a N--facing window or a light box for 3mfacing window or a light box for 3m


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Monitor for changes in appearanceMonitor for changes in appearance(Subjective measurements)(Subjective measurements)

HomogeneityHomogeneity

ColourColourGlass slidesGlass slides

MicroscopeMicroscope

Texture and skin feelTexture and skin feel

OdourOdour


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Monitor emulsion stabilityMonitor emulsion stability(Physical changes)(Physical changes)

Emulsion breakdownEmulsion breakdown Creaming or settlingCreaming or settling

Glass slidesGlass slidesaeration and density/opacityaeration and density/opacity MicroscopeMicroscope droplet size changes; crystalsdroplet size changes; crystals

Viscosity changesViscosity changes

Rheological changesRheological changes

Centrifuge testsCentrifuge tests

TurbiscanTurbiscan LumifugeLumifuge


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Emulsion CreamingEmulsion Creaming

3 months at 40C 18 months at RT

What ways are available for quicker results


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4 days at room temperature1 month at 45C

1 month at room temperature

4 days at room temperature 1 month at 45C1 month at room temperature

Microscope ExaminationMicroscope Examination


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Viscosity ChangesViscosity Changes

These are actualviscosity graphsof 5 differentw/o emulsions

differing only inemulsifier used


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Rheological ChangesRheological Changes

For suspensions measure yield valuesFor suspensions measure yield values

Yield value is the minimum force necessary toYield value is the minimum force necessary to

induce flowinduce flow

Measured using a rheometer or a BrookfieldMeasured using a rheometer or a BrookfieldDigital Viscometer with small sample adaptorDigital Viscometer with small sample adaptor

Yield values may be used to determine theYield values may be used to determine the

suspending power of a composition; verysuspending power of a composition; very

useful when developing scrubsuseful when developing scrubs http://www.connock.co.uk/articles_exfoliants.htmhttp://www.connock.co.uk/articles_exfoliants.htm


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Accelerated Stability TestingAccelerated Stability Testing

CentrifugeCentrifuge 5 minutes or more at 5,000 rpm5 minutes or more at 5,000 rpm

UltracentrifugeUltracentrifuge

A centrifuge designed to run at very high speeds andA centrifuge designed to run at very high speeds andthus generate very high centrifugal force is called anthus generate very high centrifugal force is called an

ultracentrifuge.ultracentrifuge.

Suspensions which would settle only very slowly orSuspensions which would settle only very slowly or

not at all under gravity can be made to separatenot at all under gravity can be made to separate

quickly in such a device!quickly in such a device!


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The LUMiFuge

Demixing phenomena, like sedimentation, flotation or consolidation

are directly measured by the LUMiReader, LUMiFugeor

LUMiSizerdue to the patented cutting-edge STEP-Technology.

This permits to obtain Space- and Time-resolved Extinction Profiles

over the entire sample length of up to 12 different samples

simultaneously. Parallel light (I0) illuminates the entire sample cell

and the transmitted light I is detected by thousands of sensors

arranged linearly across your whole sample fromtop to bottom with

a microscale resolution. Transmission is converted into extinction by

lg I/I0 and particle concentration may be calculated.www.lum-gmbh.com/pages/.../lumifuge/products_lumifuge.htm


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The LumiFugeThe LumiFuge

The multisampleThe multisampleanalytical centrifugeanalytical centrifugeLUMiFugeLUMiFugeacceleratesacceleratesthe demixing process upthe demixing process upto 2300 times comparedto 2300 times compared

to traditional test tubeto traditional test tubetests. Stability tests andtests. Stability tests andshelfshelf--life determinationslife determinationsof original dispersions areof original dispersions areup to 2500 times fasterup to 2500 times fasterthan performed in a testthan performed in a test

tube under earth gravitytube under earth gravity..

http://www.lum-gmbh.com/pages/products/lumifuge/products_lumifuge.htm


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TurbiscanTurbiscan

The Turbiscanmeasures transmittedand reflected lightpassing through asample and graphs the

results. Differencesover time are due tochanges in droplet sizeand distribution

www.formulaction.com/stab_lab_gb.htm


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Particle size variation

Coalescence or flocculation

Particle migration

Sedimentation or creaming

t=0 min

t=15 min

t=0 min

t=15 min

Principle of Measurement


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Monitor chemical changesMonitor chemical changes

pHpH

Loss of activityLoss of activity

VitaminsVitaminsAntioxidantsAntioxidants

EnzymesEnzymes

PreservativesPreservatives

UV FiltersUV Filters

PhotoPhoto--degradation of UV filtersdegradation of UV filters


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Monitor preservative efficacyMonitor preservative efficacy

Initial challenge test to accepted protocolsInitial challenge test to accepted protocols

CTFA, CTPA, B.P. and European PharmacopoeiasCTFA, CTPA, B.P. and European Pharmacopoeias

Head space testHead space testIt is recommended that this be done if wideIt is recommended that this be done if wide--

mouthed container is used to assess risk of mouldmouthed container is used to assess risk of mould

and fungal growthand fungal growth

Challenge testing of stability samplesChallenge testing of stability samples

It is recommended that this be done after 3 monthsIt is recommended that this be done after 3 months

stability testing at RT and 40Cstability testing at RT and 40C


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Packaging CompatibilityPackaging Compatibility

STRESS CRACKINGSTRESS CRACKING--The Hedley TestThe Hedley Test

Applied to detergent/oil based products whichApplied to detergent/oil based products which

are contained in polythene, PVC, PET.are contained in polythene, PVC, PET.

12 samples filled to the declared volume and12 samples filled to the declared volume andclosure fitted to the correct torque.closure fitted to the correct torque.

Stored at 60Stored at 60C for 48 hours, 6 upright and 6C for 48 hours, 6 upright and 6

inverted.inverted.

At the end of the test no containers should showAt the end of the test no containers should showany signs of cracking.any signs of cracking.


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Packaging ProblemsPackaging Problems

Panelling of polyethylenePanelling of polyethylene

Dissolving of PVCDissolving of PVC

Oils causing brittle polystyreneOils causing brittle polystyrene

Corrosion of aluminiumCorrosion of aluminium Discolouration of plasticDiscolouration of plastic

Transpiration of perfume through plasticTranspiration of perfume through plastic

Absorption of actives by pack wallAbsorption of actives by pack wall Etc.Etc.


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Product StabilityProduct Stability

What is it?What is it?




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Emulsion StabilityEmulsion Stability

A two-phase system, consisting of twocompletely immiscible or partially miscibleliquids, one being dispersed in the other in

the form of very fine droplets Water-in-Oil = w/o

Oil-in-Water = o/w

Oil-in-Water-in-Silicone = o/w/Si


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What makes it stable?What makes it stable?

Correct choice of emulsifier systemCorrect choice of emulsifier system

Compatible ingredientsCompatible ingredients

Compatible pHCompatible pH Correct mixing methodCorrect mixing method

Compliance with specificationCompliance with specification

Compatible packagingCompatible packaging

Understanding possible causes of instabilityUnderstanding possible causes of instability


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HLB SystemHLB System

HLB Number = E + P

5

where

E = molecular weight percent of ethylene oxide content P = molecular weight percent of polyol content

In the equation above the value (E+P) can take on anyvalue up to a maximum of 100. This means that the HLB

number assigned to the emulsifier will lie within therange of 0 to 20.


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HLB SystemHLB System

HLB number of surfactant and type ofemulsion formed

< 3 none

3 8 water-in-oil (W/O) 8 15 oil-in-water (O/W)

> 15 solubilisation


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Liquid CrystalsLiquid Crystals

Some emulsifier systems form liquid crystal structures,Some emulsifier systems form liquid crystal structures,which contribute to stabilitywhich contribute to stability

Examples:Examples:

Cetearyl glucoside with cetearyl alcoholCetearyl glucoside with cetearyl alcohol

Sorbitan olivate and cetearyl olivateSorbitan olivate and cetearyl olivate

Sorbitan stearate with sorbityl laurateSorbitan stearate with sorbityl laurate

Sorbitan stearate with sucrose cocoateSorbitan stearate with sucrose cocoate

PolyglycerylPolyglyceryl--3 methylglucose distearate3 methylglucose distearate

Potassium cetyl phosphate and hydrogenated palmPotassium cetyl phosphate and hydrogenated palm

glyceridesglycerides Lauryl glucoside & polyglycerylLauryl glucoside & polyglyceryl--2 dipolyhydroxystearate2 dipolyhydroxystearate


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Liquid Crystal EmulsionLiquid Crystal Emulsion


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Liquid Crystal EmulsionLiquid Crystal Emulsion


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Other EmulsifiersOther Emulsifiers

Polymers e.g. Acrylates/C10-30 Alkyl AcrylateCrosspolymers

Polyethylene glycol ethers (Oleth-10; Laureth-10 etc)

Polysorbates with Sorbitan esters e.g. Polysorbate-20with Sorbitan monolaurate

Glyceryl esters e.g. Glyceryl cocoate / laurate etc.

Alkolylated dimethicones (AKA Dimethicone copolyols)

Soaps e.g. triethanolamine stearate; Potassiumpeanutate etc.

PG Esters e.g. Propylene glycol myristate etc.

Sucrose esters e.g. Sucrose laurate / myristate etc


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Incompatible IngredientsIncompatible Ingredients

Carbomers and saltsCarbomers and salts

Kathon CG contains a saltKathon CG contains a salt

Dihydroxyacetone and formaldehydeDihydroxyacetone and formaldehyde

Many preservatives are formaldehyde donorsMany preservatives are formaldehyde donors

Enzymes and chelating agentsEnzymes and chelating agents

EDTA and its saltsEDTA and its salts

ParabensParabens

EthoxylatedEthoxylatedemulsifiersemulsifiers etc. etc.etc. etc.


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pH vs ViscositypH vs Viscosity

84000

86000

88000

90000

92000

94000

96000

98000

100000

pH 5.0 pH 5.5 pH 6.0 pH 6.5 pH 7.0 pH 7.5 pH 8.0

Viscosity

Typical carbomer system


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Correct Mixing MethodsCorrect Mixing Methods

Use laboratoryUse laboratory

mixing equipmentmixing equipment

which representswhich represents

that availablethat availablein the factoryin the factory


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Pilot ScalePilot Scale


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Correct Mixing MethodsCorrect Mixing Methods


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Compliance with SpecificationCompliance with Specification

How was the specification set?How was the specification set? One small laboratory batch?One small laboratory batch?

2 or more laboratory batches with2 or more laboratory batches withreproducible results?reproducible results?

Pilot scale batch?Pilot scale batch?

Was stability tested on a product withinWas stability tested on a product withinthe specification set?the specification set? Better still; were 2 or more batches at limitsBetter still; were 2 or more batches at limits

of specification testedof specification tested


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What causes instability?What causes instability?

For an emulsion to become unstable thedispersed phase droplets must collide andcoalesce

Coalescence of two dispersed phasedroplets produces a bigger dispersedphase droplet, and the ultimate outcomeof this process is complete phaseseparation, indicating emulsion instability


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Forces of AttractionForces of Attraction

F = -Aa

12H

where

F = London-Van der Waals force of attraction

A = Hamaker constant

a = radius of the dispersed phase droplets

H = distance between two adjacent dispersed

phase droplets


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Forces of AttractionForces of Attraction

Good stuff but what does it mean forGood stuff but what does it mean for

emulsion stabilityemulsion stability

From the equation it can be seen that the

magnitude of the attractive force increasesas the radius of the dispersed phase

droplets becomes larger and less as thedistance between them is increased

Stability = Small droplets far apart

F = -Aa12H


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Stokes Law

Stokes Lawdescribes the factors influencing the velocityof a solid sphere, moving under the force of gravity, in acontinuous liquid medium

V = 2a2(cd)g

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V = velocity of the dispersed phase droplet a = radius of the dispersed phase droplet d = density of the dispersed phase c = density of the continuous phase g = acceleration due to gravity = viscosity of the continuous phase


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Stokes Law: Good stuff but whatStokes Law: Good stuff but what

does it mean for emulsion stabilitydoes it mean for emulsion stabilityV = 2a2(cd)g

9

To improve stability reduce V

Reduce a - size of dispersed phase droplet

Reduce (pc-pd) by matching density of the dispersedphase with that of the continuous phase

g = acceleration due to gravity difficult to alter Increase - viscosity of the continuous phase


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What droplet size?What droplet size?

Emulsion appearance and approximateparticle size

milky-white greater than 1

blue-grey 1.0 - 0.1

translucent 0.1 - 0.05

transparent less than 0.05


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Careful selection of emulsifiersCareful selection of emulsifiers

Small droplet size (High shear mixing; PITSmall droplet size (High shear mixing; PITtechnology)technology)

Lamellar structures by using emulsifiersLamellar structures by using emulsifiersthat form liquid crystalsthat form liquid crystals

Match SG of oil phase to aqueous phaseMatch SG of oil phase to aqueous phase

Adjust rheological properties by usingAdjust rheological properties by using

carbomers or xanthan gum, starch or CMCcarbomers or xanthan gum, starch or CMCderivatives etc.derivatives etc.


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Add Rheological AdditiveAdd Rheological Additive

0% UltraThix P-100+ 0.5% Cerasynt 945

0.5% UltraThix P-100+ 0.2% Cerasynt 945

0.5%UltraThix P-100+ 0.5%

Cerasynt 945

Cerasynt 945 = Glyceryl stearate (&)laureth-23 Ultrathix P100 =

Acrylic acid/VP Crosspolymer


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Add Right Rheological AdditiveAdd Right Rheological Additive

Zinc Oxide nano particles

Carbomer Acrylic acid/VP Crosspolymer


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Microscope ExaminationMicroscope Examination

Titanium Dioxide Nano particles

Carbomer Acrylic acid/VP Crosspolymer


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Sun Protection ProductsSun Protection Products

These present special problemsThese present special problems

Emulsion stabilityEmulsion stability

Agglomeration of micronised sunscreensAgglomeration of micronised sunscreens

Crystallising of organic sunscreensCrystallising of organic sunscreens Failure to meet SPF declarationFailure to meet SPF declaration

Failure to meet UVA requirementsFailure to meet UVA requirements

Failure to meet water resistance claimsFailure to meet water resistance claims

Photodegradation of activesPhotodegradation of actives


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Agglomeration of micronised sunscreens canAgglomeration of micronised sunscreens can

be seen under a microscope at 1000xbe seen under a microscope at 1000x

magnificationmagnification

Use rheology modifiers to stop migration ofUse rheology modifiers to stop migration ofparticlesparticlesVeegum is good.Veegum is good. Acrylic acid/VPCrosspolymer is recommended


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Preventing AgglomerationPreventing Agglomeration

Zinc Oxide nano particles

Acrylic acid/VP Crosspolymer

TiO2 Nano particles


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Crystallising of Organic SunscreensCrystallising of Organic Sunscreens

Check solubility in oil phase

If using Phenylbenzimidazole Sulfonic AcidpH 7.3 - 7.7 is critical


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Photodegradation of BMDBMPhotodegradation of BMDBM


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Improve UV Absorber StabilityImprove UV Absorber Stability

The UVA filter BMDBM is not photostable and may lose 60% orThe UVA filter BMDBM is not photostable and may lose 60% ormore of its activity at 360nm when exposed to solar radiation.more of its activity at 360nm when exposed to solar radiation.

EHMC destabilises BMDBM / octocrylene mixturesEHMC destabilises BMDBM / octocrylene mixtures

BenzophenoneBenzophenone--3 stabilises BMDBM weakly; octocrylene stabilises3 stabilises BMDBM weakly; octocrylene stabilises

EHMC strongly but does not stabilise BMDBM and ethylhexylEHMC strongly but does not stabilise BMDBM and ethylhexylmethoxycrylene stabilises BMDBM strongly.methoxycrylene stabilises BMDBM strongly.

There is a relationship between the rate of photo decay of BMDBMThere is a relationship between the rate of photo decay of BMDBM

and the dielectric constant of the oil phase. As the dielectricand the dielectric constant of the oil phase. As the dielectric

constant increases BMDBM is progressively more stable until itconstant increases BMDBM is progressively more stable until it

reaches maximum stability at about 8.8, after which its rate ofreaches maximum stability at about 8.8, after which its rate of

decay increases againdecay increases again


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Failure to meet SPF declarationFailure to meet SPF declaration

Failure to meet UVA requirementsFailure to meet UVA requirements

Study the suppliers literature and many articles on theStudy the suppliers literature and many articles on the

subjectsubject

http://www.creativehttp://www.creative--developments.co.uk/papers/developments.co.uk/papers/

http://www.cosmeticsbusiness.com/section.asp?navcode=50http://www.cosmeticsbusiness.com/section.asp?navcode=50

DonDont put to much faith in SPF boosterst put to much faith in SPF boosters

Use the Ciba Sunscreen Simulator then inUse the Ciba Sunscreen Simulator then in--vitro then invitro then in--vivovivo

http://http://www.ciba.com/index/indwww.ciba.com/index/ind--index/indindex/ind--per_car/indper_car/ind--pcpc--uv/induv/ind--pcpc--uvuv--sss.htmsss.htm

Make sure the formula complies with latest EUMake sure the formula complies with latest EU

Recommendation (UVA =>1/3Recommendation (UVA =>1/3rdrd UVB)UVB)


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Thank you for your timeThank you for your timeand may all your creationsand may all your creations

be stablebe stable

John WoodruffJohn Woodruff

www.creativewww.creative--developments.co.ukdevelopments.co.uk

Documents

Cosmetic Product Stability