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Emulsions & Sunscreens: An Update

Ken Klein

Definition

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An emulsion is a system of two (or more) immiscible materials (usually liquids) in which one material (the dispersed/internal phase) is suspended or dispersed throughout another material (the continuous/external phase) in separate droplets

Typical Emulsion Components (water phase)

Water Humectant Preservative Emulsifier Thickener Emollient "Whiffle dust" QS 2-7% 0.05-1.0 0.5-1.5% 0.1-2% 0.5-2% QS

Typical Emulsion Components (oil phase)

Emollients "Actives" Antioxidant Emulsifier (primary) Emulsifier (secondary) Wax Silicones 5-10% Drug level 0.05-0.2% 1-2% 1-2% 0.5-2% 0.5-5%

Typical Emulsion Components (misc.)

Preservative Fragrance Color qs 0.1-1% qs

Emulsifiers:Function

! !

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Reduce surface tension Form complex interfacial films (on the surface of emulsion droplets) Form liquid crystalline structures which act as a barrier to coalescence

Comment

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All emulsions are inherently unstable (with the exception of spontaneously forming micro emulsions). All we can do is delay the day when the instability will arrive.*

*Barker, Graham

Stokes Law

V=d2(p)g/18

Goal= Reduce the value of V

V=Velocity of sedimentation

d=diameter of particles of the dispersed phase p =difference between the specific gravity of the internal and external phases g=acceleration due to gravity =viscosity of the external phase

Stabilization

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Increase viscosity Decrease particle size and obtain a narrow distribution of particle sizes Improve strength of interfacial film

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Choice of emulsifier

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Reduce particle interaction Preservation considerations

Viscosity Effects

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Increase % (phase ratio) of internal phase Decrease particle size

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The internal phase occupies a greater volume At higher concentrations you interfere with the electrical double layer and destabilize emulsions Destabilizes O/W emulsions Stabilizes many W/O emulsions Stabilizes many Cationic emulsions

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Add electrolyte (monovalent)

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Emulsion Stabilization (on the micro level)

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Electrical charges (double layer) Solvated layers (liquid crystals?) Surface rigidity/elasticity Steric effects (emulsifier packing)

Particle Size Influences

! ! ! ! !

You MUST have small particles and a narrow distribution of particle sizes Choice of emulsifier Placement of emulsifier Concentration of emulsifier Processing

! ! !

Phasing Mixing equipment Temperature effects

Ostwald Ripening

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The phenomenon whereby smaller droplets seem to disappear and larger droplets grow in size

!

!

Small droplets have a high radius of curvature. This leads to an increased outward pressure (Laplace pressure) and to greater solubility of the oil components in the water phase. Diffusion then occurs from the water phase into the larger oil droplets which are seen to grow in size. The result is emulsion instability!

Cognis Skin Care, Dr. R. Daniels

Fatty Alcohol Adsorption

Interfacial Film Strength

Steric Stabilization

!

The term steric stabilization is generally used to describe stabilizing action of polymers adsorbed on the surface of the discontinuous phase (droplets) of dispersions and emulsions. It is also known as colloidal protection. I.E Heller and L. Pugh; J. Chem. Phys., 22, 1778(1956)

W/O Steric Stabilizing Emulsifier

Hydrophobically Modified Polymeric Emulsifier

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Pemulen (B.F. Goodrich) High molecular weight polyacrylate C10-30 alkyl crosspolymers Oil-in-water emulsifier Stabilizes emulsions through polyanionic (negative charge on hydrophobe)steric stabilization

Synthetic Thickeners

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Carbomer

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Acrylic acid polymer Available in several grades

! ! !

ETD (Easy To Disperse), more salt tolerant? Ultrez...Easy to disperse Various viscosity grades

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Positives

Excellent high temperature stability/viscosity, good suspension characteristics Negatives ! Poor electrolyte tolerance ! Must be neutralized ! Not compatible with cationics

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!

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Use level (emulsions)

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0.1-0.5%

Aculyn 22

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Acrylic polymer emulsion (30%)

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INCI

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Acrylates/Steareth-20 Methracylate Copolymer Easy to incorporate, good high temperature viscosity Must be used (neutralized)at pH 7 and above

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Positives

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Negatives

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Sepigel 305

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Polymer emulsion (30%)

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INCI

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Polyacrylamide (and) C13-14 isoparaffin (and) laureth-7 Easy to incorporate, good high temperature viscosity Good compatibility with zinc oxide, good low pH tolerance Off odor, expensive, difficult to control viscosity

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Positives

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Negatives

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Salcare SC 96

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Polymer emulsion (30%)

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INCI

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Polyquaternium-37 (and) propylene glycol dicaprylate/dicaprate (and) PPG-1 Trideceth-6 Easy to incorporate, good high temperature viscosity Good compatibility with zinc oxide, good low pH tolerance cationic Off odor, expensive, difficult to control viscosity Incompatible with anionic materials

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Positives

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!

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Negatives

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Cellulose based thickeners

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Excellent stability vs. pH High use levels needed to build viscosity (1-2%) Anionic and nonionic versions available Can thicken alcohol (hydroxypropyl cellulose)

Natural Thickeners

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Acacia-Gum Arabic

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Polysaccharide Hydrocolloid, odorless Seaweed odor Seaweed derived polysaccharide, good slip Polysaccharide, odorless Anionic polysaccharide, fermentation product Good electrolyte and pH tolerance Maintains viscosity at elevated temperatures

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Algin-Sodium Alginate

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Carrageenan

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Locust bean gum

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Xanthan Gum

! ! !

Inorganic Thickeners

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Bentonite (clay derived)

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Used as a suspending agent. Can be used to stabilize w/o emulsions. Available as preblended gels (cyclomethicone, IPM, etc.) Thixotropic agent Delicate formulation parameters Water insoluble Good suspending agent Usually combined with other thickeners Good pH, electrolyte tolerance

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Laponite- Sodium magnesium silicate

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Magnesium Aluminum Silicate

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Misc. Thickeners

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High melting point waxes

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Beeswax Carnauba Cetyl Stearyl Behenyl Thickens oil phase

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Fatty alcohols

! ! !

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Fumed Silica

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Methods For Choosing Emulsifiers

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HLB

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Hydrophilic Lipophilic Balance Dr. T. J. Lin Phase Inversion Temperature

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Water Solubilization

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PIT

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Dr. Shinoda

HLB

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! ! !

Invented in 1949 by Griffin. Assigns a number from 1 to 20 to emulsifiers based on % weight of Hydrophobe to Lipophobe in a molecule. Used almost exclusively for nonionic emulsions HLB below 9...w/o HLB 9-10..? HLB above 10...o/w

HLB

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Oils have a required HLB Generally one should blend high and low HLB emulsifiers to get the best emulsion HLB of ethoxylated emulsifiers

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HLB=E/5 where E= weight % of ethylene oxide

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Positives

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HLB

Excellent starting point Generally produces a fairly good emulsion Ignores the importance of:

! ! ! ! ! ! ! !

!

Negatives

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Electrical double layer Temperature effects of ethoxylates Fatty alcohols Placement of emulsifier % of emulsifier to be used Phase volume ratios Component interactions Liquid crystals

Water Solubilization: Dr. T. J. Lin

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A method to choose emulsifiers Addresses most of the drawbacks of the HLB system

Water Solubilization: Dr. T. J. Lin

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The ability of the oil phase (with oil phase emulsifiers) to solubilize water is inversely proportional to the final particle size of the emulsion

Water Solubilization: Dr. T. J. Lin

!

!

The oil phase is heated to emulsification temperature and stirred. Water is slowly added until a cloudy oil phase is seen. This method can be used to:

! ! !

Choose emulsifiers Determine optimal concentration of emulsifiers Determine effects of "oil" components on emulsion stability

Water Solubilization

Water

Oil Phase

Heat

Water Solubilization: A "Trick"

! !

Pretreat the oil phase! Improves/reduces particle size distribution

PIT: Phase Inversion

Temperature

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Dr. Shinoda The temperature at which the emulsion inverts due to nonionic (ethoxylates)/ interactions.

PIT

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As the temperature increases, the water solubility of ethoxylated nonionic emulsifiers becomes poorer (the HLB decreases). There is a temperature (PIT) at which the Hydrophilic and Lipophilic characteristics of the emulsifier are equal (relative to the required HLB of the oil phase). At this temperature the emulsion will exhibit a phase inversion. The PIT should be at least 20C higher than the storage temperature. Choose emulsifiers, and concentrations, to raise the PIT.

Liquid Crystals:

A Definition

Highly anisotropic fluids that exist as a result of long-range orientational ordering among constituent molecules. Also: Three dimensional association structures which stabilize emulsions.

Liquid Crystals In Emulsions

Suzuki, Tsutsumi and Ishida: The self bodying action of fatty alcohols is caused by the formation of a network structure of liquid crystalline phase in the emulsion system

Liquid Crystals

This ordering is adequate to provide for increased viscosity, but not strong enough to prevent flow, thus viscous liquids are typical. This dualism between a solid (crystal) and a flowing liquid gives rise to the term liquid crystal. High temperatures will destroy the fine structure resulting in an isotropic liquid. Upon cooling the structure may or may not reform.

Mechanism Of Stabilization

!

!

A barrier forms around the emulsion droplets and strengthens the o/w interface. A gel network is formed which extends from the surface of the droplets out into the bulk of the external phase. This increases the viscosity and impedes droplet movement.

Liquid Crystal Emulsifiers

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Mimic the lipid bilayer in all skin cells Good barrier function

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Reduce TEWL?

! ! !

For sensitive skin Delivery System for Vitamins Ideal for sunscreens

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Low HLB emulsifiers

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Arlatone 2121

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Liquid Crystal Emulsifiers

Sorbitan Stearate and Sucrose Cocoate Low HLB

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Place in water phase

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Stepan-Mild RM1

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Sodium Stearyl Phthalamate Polyglyceryl-10 pentastearate and behenyl alcohol and sodium stearoyl lactylate Cetearyl glucoside

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Nikkomulese 41

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Montanov 68/Emulgade 68/50

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SPF 8 Self Tanner With Zenigloss Q-SE Liquid Crystal Stabilized

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Phase A ! DEIONIZED WATER ! DISODIUM EDTA ! GLYCERIN 96% ! XANTHAN GUM ! ARLATONE 2121(SORBITAN STEARATE AND SUCROSE COCOATE)

QS 0.1 2.0 0.3 2.5

!

PHASE B

! ! ! ! ! ! ! !

OCTYL METHOXYCINNAMATE OCTYL SALICYLATE ZENIGLOSS Q-SE LEXOREZ TL8 (TRIMETHYLPENTANEDIOL/ADIPIC ACID COPOLYMER) ZENIGLOSS SE TOCOPHERYL ACETATE BHT DIOCTYL SEBACATE

7.5 5.0 2.5 3.0 2.5 0.1 0.05 5.0

!

PHASE C

! ! !

ARLASOLVE DMI (DIMETHYL ISOSORBIDE) TRANSCUTOL (ETHOXYDIGLYCOL) DHA

3.0 5.0 5.0

!

PHASE D

! ! !

DEIONIZED WATER SODIUM METABISULFITE CITRIC ACID TO Ph 4.0

5.0 0.3 qs

!

PHASE E

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PHENONIP

1.0

Cationic Emulsifiers Positively Charged Hydrophobe

R

!

[R-N-R] Cl

R

+

-

Excellent Skin Feel, easy to preserve, low use levels. Can be irritating.

DRY SKIN MOISTURIZER (CATIONIC)

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Phase A ! DEIONIZED WATER ! DISODIUM EDTA ! GLYCERIN 96% ! SALCARE SC96 PHASE B ! CYCLOMETHICONE PENTAMER ! ZENIGLOSS Q-SE ! ZENIBEE CREAM ! TOCOPHERYL ACETATE ! DIMETHICONE ! CETEARYL ALCOHOL ! GLYCERYL STEARATE

QS 0.1 3.0 3.0

!

5.0 5.0 3.0 0.1 3.0 2.5 0.05 1.0

!

PHASE C

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GERMABEN II

Nonionics

! ! !

Ethoxylates Predominate Broadly compatible Best stability is achieved by combining with ionic emulsifiers.

W/O Emulsions Applications

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Protective creams

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Forms a water resistant barrier against water and water soluble irritants Reduces TEWL

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Moisturizer

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! ! ! !

Cleansing creams Sunscreen lotions Baby lotions Make-up products

W/O Emulsions Disadvantages

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!

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Higher cost of goods than o/w systems More difficult to manufacture and clean up Inherently less stable due to lack of cohesive double layer effect Often give a greasy occlusive skin feel

W/O Polymeric Emulsifier

DRY SKIN MOISTURIZER (W/0)

!

Phase A ! DEIONIZED WATER ! DISODIUM EDTA ! GLYCERIN 96% ! SODIUM CHLORIDE ! GERMABEN II PHASE B ! CYCLOMETHICONE PENTAMER ! ZENIGLOSS Q-SE (or) ZENIGLOSS SE ! ZENIBEE CREAM ! TOCOPHERYL ACETATE ! DIMETHICONE ! CASTORWAX MP80 (HYDROGENATED CASTOR OIL) ! ABIL EM90 (CETYL DIMETHICONE COPOLYOL)

QS 0.1 3.0 0.75 1.0 2.0 1.0 3.0 0.1 3.0 2.0 4.5

!

Sunscreens: The Basics

Types of Solar UV Radiation

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UVAI (340-400nm)

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Can cause tanning but has minimal erythemal effect. Can cause long-term damage. Penetrates deeply. Slight erythemal contribution Causes sunburn and is a major contributor to skin cancer development. Very energetic radiation. Absorbed by the ozone layer.

!

UVAII (320-340nm)

!

!

UVB (290-320nm)

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UVC (200-290nm)

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Ultraviolet Wavelengths

Absorbtivity

1 0.8 0.6 0.4 0.2 0 200

Typical UVB Sunscreen absorbance

UVC UVB

UVA

Filtered out by ozone Sunburn Causes wrinkling/aging Cancer layer UVAII UVAI Energy

Skin Penetration

220

240

260

280

300

320

340

360

380

400

Wavelength (nm)

SPF

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MED

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Minimum Erythemal Dose MED(ps)/MED(us) ((SPF-1)/SPF))*100

! ! ! !

!

Sun Protection Factor

!

!

% UVB Absorbed (Sayre)

!

SPF SPF SPF SPF

2 absorbs 50% 15 absorbs 93.3% 30 absorbs 96.7% 50 absorbs 98%

vs. Erythemal Effectiveness

(Diffey, B., J. Soc. Cosmet.Chem., 40, 127-133)

Wavelength

295 300 305 310 315 320 325 340 350 360 370 400

Erythemal Effectiveness

1.0 0.65 0.22 0.07 0.02 0.009 0.003 0.001 0.0007 0.0005 0.0003 0.0001

UVB Reflectivity vs. Surface

(Lilyquist) Surface Fresh Snow Old/Dirty Snow Water Sand White Skin % UVB Reflected 85 50 9 17 1

Drug Definition

a. Articles recognized in the official United States Pharmacopoeia, official Homeopathic Pharmacopoeia of the United States, or Official National Formulary, of any supplement of them, b. Articles intended for the use in the diagnosis, cure, mitigation or treatment of disease in man or other animals c. Articles (other than food) intended to affect the structure or any function of the body of man or other animals, d. Articles, intended for use as a component of any articles specified in (a,b or c)

Final Monograph

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! !

16 Approved (meets monograph conditions) Sunscreens Maximum SPF...30+ Sun block

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Not a permitted claim Not a permitted claim

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SPF 0 and 1

!

Final Monograph

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Waterproof

!

!

Expanded Claims ("8 hour", "abrasion resistant") are not permitted Static testing not required for water resistance claims

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IR Claims are non-drug claims

Final Monograph

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UVA Efficacy Evaluation

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Eyrthema IPD

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Immediate Pigment Darkening

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PPD UVA/UVB Ratio

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Star System Critical Wavelength

Final Monograph

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No Minimum Use Levels Of Sunscreens

!

The "concentration of each active sunscreen ingredient in a combination product must be sufficient to contribute a minimum SPF of 2 to the finished product and the finished product must have a minimum SPF of not less than the number of sunscreen actives used in combination multiplied by 2."

Final Monograph

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UVA

!

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Will be addressed in a future issue of the Federal Register Testing

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"chemical free" "PABA Free"

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Aminobenzoic acid (PABA) Free

Courtesy of: Dave Steinberg

Approved Sunscreens

Sunscreen

Aminobenzoic Acid Avobenzone Cinoxate Dioxybenzone Homosalate Menthyl Anthranilate (Meradimate) Octocrylene Octyl Methoxycinnamate (Octinoxate)

Maximum %

15 3 3 3 15 5 10 7.5

Approved Sunscreens

Sunscreen

Octyl Salicylate (Octisalate) Oxybenzone Padimate O Phenylbenzimidazole Sulfonic Acid (Ensulizole) Sulisobenzone Titanium Dioxide Trolamine Salicylate Zinc Oxide

Maximum %

5 6 8 4 10 25 12 25

Sunscreen Chemistry

Why did the white bear dissolve in water?

It was a POLAR bear

Sunscreen Chemistry

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Ground StateExcited State Ground State

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Energy given off as:

! ! ! ! !

IR Cis/trans isomerization Fluorescence Phosphorescence Visible

Sunscreen Chemistry

!

Solvent effects

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Nonpolar solvents stabilize the ground state of sunscreens that are nonpolar and thus greater energy (shorter wavelength) is needed to excite these sunscreens. Their curves are seen to shift to the left (shorter wavelength). Typically the SPF decreases.

Avobenzone

! !

KetoEnol Tautomerism Stability Issues

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Patents

! ! !

Octocrylene (L'Oreal) Methyl benzylidine camphor (P&G) Hallbrite TQ (di-octyl naphathlate)

!

Triplet Quenching Particulates formaldehyde

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Formulation Issues

! !

Particulate Sunscreens

!

Mechanism of action

!

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Particles smaller than 150nm will block/scatter UV but not exhibit whitening on the skin Increase of optical path length

Mechanism Of Particulate Absorption

(Anderson)

Titanium Dioxide

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Two Crystalline Forms

!

Anatase

!

Photo unstable Photo stable

!

Rutile

!

Zinc Oxide

! !

UVA/UVB absorbance Formulation Issues

! ! !

Use dispersant to reduce agglomeration Use suspending agent Avoid materials sensitive to polyvalent materials

! !

Fatty acids Carbomers

Sunscreen Chemistry

!

Solubility Parameter Considerations

!

(Vaughan, C.)

If the solubility parameter (a measure of polarity) of the sunscreen is not matched to the solubility parameter of the oil phase, agglomeration will result with a decrease in the SPF.

Sunscreen Agglomeration

(Solubility Parameter Effects)

!

The Solubility Parameters of sunscreens and solvents must be matched to give optimal performance

Sunscreen OMC Padimate O Dimethylisosorbide Octocrylene Solubility Parameter 9.3 9.1 9.2 9.3

!

Sunscreen UV Absorption

(Solubility Parameter Effects)

!

Sunscreen (mixture) Mineral oil/Padimate O

Low conc. 97% Mineral oil/Padimate O/co solvent 99% Mineral oil/Padimate O/co solvent/Polymer -----

High conc. 21% 54% 100%

Vehicles

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Emulsions

! !

! ! ! ! !

Hydro alcoholic Sticks Ointments Gels Aerosols

! !

O/W W/O

Foams Sprays

! !

Propellant Pumps

Optimizing Formulations

! ! !

SPF Water resistance Mildness

Optimizing SPF

!

Residual Skin Film

!

Thickness

!

Optical path length

!

Uniformity

!

! ! !

Absorb maximally in the UVB region and up to 340nm Use the correct vehicle Combine particulates and organic sunscreens solubility parameter considerations

Optimizing Water Resistance

! !

Water insoluble sunscreens Use hydrophobic vehicles

! ! ! !

W/O emulsions Ointments Sticks Oils

Optimizing Water Resistance

!

O/W emulsions

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Minimum levels of hydrophilic emulsifiers

! !

Soaps Highly ethoxylated emulsifiers

! ! !

Use High Oil Levels Film formers/resins Acrylates/C10-30 alkyl acrylate crosspolymer (Pemulen)

Optimizing Water Resistance

!

Have emulsion break or invert from O/W to W/O during application

Formulating Mild Sunscreen Formulations

!

Minimum emulsifier levels

!

Avoid soap based systems

! ! ! !

Minimum levels of preservative Minimum levels of fragrance Minimum levels of sunscreens Use long chain "oils"

IR Effects

! !

(Dr. Ken Marenus)

! !

IR: 700-1000nm When cells (keratinocytes and fibroblasts are damaged they release arachidonic acid) Antioxidants inhibit IR damage (Vitamin E linoleate, BHT, etc.) TiO2 protects from IR damage

!

! ! !

Test: Measure time needed to heat a petri dish of water, coat with sunscreen and repeat measurement 1 MED (UVB)=75mJ/cm2...10-20 minutes 1 MED (UVA)=10J/cm2...50 minutes 1 MED (IR)=40mJ/cm2...180 minutes

SPF 30 KIDS SUNSCREEN STICK With Zenigloss S

!

Phase A ! WHITE CERASIN WAX ! CARNAUBA WAX ! ALOE OIL ! TOCOPHERYL ACETATE ! ZENIGLOSS S ! CREMEROL HMG (HYDROXYLATED MILK GLYCERIDES) PHASE B ! OCTYL METHOXYCINNAMATE ! OCTYL SALICYLATE ! Z-COTE HP1 ! LAURYL LACTATE ! ZENIGLOSS SE ! BHT

QS 4.0 0.15 0.1 5.0 3.0

!

7.5 5.0 6.0 3.0 2.5 2.5

SPF 15 VERY WATER RESISTANT SPRAY With Zenigloss S

Phase A ! DEIONIZED WATER ! DISODIUM EDTA ! M,P DIOL ! PEMULEN TR-1 PHASE B ! OCTYL METHOXYCINNAMATE ! OCTYL SALICYLATE ! OXYBENZONE ! ZENIGLOSS SE ! ZENIGLOSS S PHASE C

!

!

QS 0.1 2.5 0.25 7.5 5.0 2.0 1.5 2.5

0.2 1.0

!

!

TRIETHANOLAMINE 99% GERMABEN II

!

PHASE D

!

THE COAT HANDLER SUNSCREEN

·Sunscreen for Pets - SPF 15 ·Imagine a sunscreen for both you and your pet! Ideal for shavedowns; Poodles that are groomed with a #40 blade; hunting and camping; non-water sports, Chinese Cresteds and other hairless breeds; helping to prevent sun damage to black coats; helping to prevent skin cancer in older pets. ·Available in 2 oz. and 8 oz. pump sprays.

© 1998 Senproco, Incorporated

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