Post on 20-Aug-2020
Lipid knowledge for the personal care industry
The function of emollients in skin care
Jari Alander2019
2
Wikipedia: “complex mixtures of chemical agents specially designed to make the external layers of the skin (epidermis) softer and more pliable”
“Emollire” (Latin) – means to soften
Emollients are usually:the main component in emulsions after water (3–20% or more) and the dominating ingredient in many anhydrous formulationsvarious chemical structures including vegetable and mineral oils, esters and siliconesseen to have different polarities (hydrophilic – lipophilic)
Despite the definition in encyclopedias – emollient is not always equal to moisturizer
Emollient – definition
3
Depends on applicationDepends on region/market
Which are the most common emollients in skin care?
Face careEU
Shea butter
Mineral oil
Dimethicone
Face care JP/KR
Mineral oil
Cyclopenta-siloxane
Squalane
Body care EU
Mineral oil
Shea butter
Dimethicone
Body care JP/KR
Dimethicone
Mineral oil
Shea butter
4
Skin softening (emolliency)Occlusive moisturizationLubricationStructure formation in formulationDelivery system/solubilizer/carrierAesthetic and sensory modifier
Functions of emollients in cosmetic formulations
5
The surface of the skin is a complex system comprising lipids, cells, proteins, microorganisms, water, natural moisturizing factors etc
Skin surface lipids are of two types– Epidermal lipids– Sebum lipids
Epidermal lipids (from keratinocytes)– Ceramides, cholesterol, free fatty acids– Typically extractable from skin surface: 5–10 μg/cm2
Sebum lipids (from sebaceous glands)– Triglycerides, squalene, free fatty acids, tocopherols– Typically extractable from the forehead: 150–300 μg/cm2
Emollients and skin
6
Sensory properties, moisturization, ingredient absorption and many other properties are determined by the interaction between the stratum corneum and the emollients from the skin care product
Stratum corneum and emollients
Keratinocytes approx 20 micrometer wideEmulsion droplets 0.1 -5 micrometers in diameter
Skin lipids
Shear rate when applyinga cosmeticproduct:500–5000 1/s!
7
Wetting of the stratum corneum by the emulsion– Surface & interfacial properties of emulsion droplets versus the
properties of the skin lipids
Rheology of emulsion– Determined by emollient properties and interaction with polymers
and emulsifiers
Solubility of emollient in stratum corneum and vice versa– Polarity of respective phases
Droplet-droplet interaction– Breaking of emulsion to create an oil film on the SC surface
Skin surface topology– Smooth versus wrinkled etc
Water release and evaporation from formulation
Physicochemical parameters affecting the interaction
8
Wortel V.A.L, Wiechers JW – Skin sensory performance of individual personal care ingredients and marketed personal care products
Sensory attributes evaluated upondifferent steps of application
Before rubbing During rubbing After rubbing
Appearance:• Thickness• Cloudiness• Shine
Appearance:• Cloudiness• Shine
Appearance• Absorbency• Shine
Sensation:• Tingling• Cooling
Feel:• Absorbency• Thickness• Oiliness• Greasiness• Stickiness• Silkiness• Moisturization
Feel• Oily residue• Sticky residue• Silky residue• Amount of residue
Sensation:• Cooling• Warming• Tingling• Odor• Spreadability
Sensation:• Cooling• Warming• Moisturization• Stiffness or tightness of skin• Tingling• Coating
9
Polarity is a 3-dimensional property (Hansen model)– Van der Waals interactions (Dispersive forces)
• Molecular size and shape– Hydrogen bonding
• Presence of –OH, -COOH, -NH2 etc groups with mobile hydrogen groups– Polarizability
• Presence of double bonds, ester and amide groups, aromatic rings etc• Measures the mobility of electron cloud around a molecule
Guiding principle – like dissolves like– If all three polarity dimensions match between solvent and solute
we have high solubility
Polarity determines interactionswith skin and between ingredients
10
Qualitative comparison ofsome liquid emollients
Liquid oil
Van der Waals
interaction Hydrogen bonding Polarizability
C12-15 AlkylBenzoate X (X) XX Large polar group, highly
polarizable
Octyldodecanol X X X Exposed hydrogen bonds
Isopropyl palmitate X (X) X Medium polar, long FA chain, polarizable
Lipex Bassol C(Olus oil/Canola oil) XX (X) X Long chains, interacting with
each other, low polar
Lipex SheaLight(Shea butter ethylesters)
X (X) XLong FA chains, exposed ester group, high polarizability
Mineral Oil XX - -Non polar, no hydrogen bonds, very strong Van derWaals
Dicaprylyl Carbonate X (X) X(X)
Small molecule, more polar than other esters due to exposed carbonyl group and short chains
11
Hansen’s Polarity ParametersLiterature data and approximations
VdW / Dispersive
Hydrogen bonding Polarizability
Mineral oil 16.3 0 0Cyclomethicone 12.9 1.3 1.0Dimethicone 12.5 0.8 0.8Lipex Bassol C 17.5 3.3 4.1Lipex SheaLight 16.2 3.8 4.5Skin 17.6 13.0 11.0Glycerol 17.4 11.3 27.2Water 15.5 16.0 42.3
12
Lipex Shea™ dispersed in variousemollients (20% butter / 80 oil)
LipexBassol C
Caprylic/ caprictriglyce-
ride
LipexShea-Light
Dica-prylylether
Isopro-pyl
isostea-rate
Paraffin oil Castor oil
13
Wetting of the skin or hair surface is important for functionality
Good wetting gives better film forming properties and more even coverage on the surface
Wetting ability is determined both by the surface and the properties of the liquid
Viscosity (rheology) determines speed of spreading while extent of spreading also depends on the polarity
Other aspects of polarity – spreading and surface interactions
14
Contact angle on hydrophobic surface (teflon)Lipex SheaLight™ is uniquely polar
• Good spreadability on skin requires that emollient and skin polarity are matched
• Skin combines both hydrophilic and lipophilic properties -> balanced polarityis required
• Skin polarity varies on the body (face vs arm etc)
Paraffinum liquidum (21)
Dimethicone (45)
15
Example 1: influence of oil phase on rheology of an emulsion
– Solid shea butter changes behavior when mixed with different emollients
Example 2: Influence of oil phase on the structure formation using beeswax in an anhydrous system
– Beeswax mixed with different oil phases gives changes in microstructure and solidification dynamics
Connecting the dots – polarity, solidity and behavior in formulation
16
Effect on flow curve of varying emollientsEmulsion with Lipex Shea™ at 20°C
Very small differences in
behavior at 20°C
17
Effect on flow curve of varying emollientsEmulsion with Lipex Shea™ at 35°C
Diffences in flowcurves due to differingsolubility of shea butter
at 35°C
70 60 50 40 30 201E-3
0,01
0,1
1
10
100
1000
10000
100000
1000000
1E7
1E8
G' [P
a]
Temperature [°C]
Castor oil Isopropylmyristate Lipex Bassol C Paraffin oil
Selection of oil phase determines microstructure
Beeswax in different carriers (15/85)
19
Emollients offer great opportunities for optimizing formulation rheology, stability and skin feel
Consider chemical structure and physical properties for finetuning application properties:– Polarity (molecular size, hydrogen bonds, polarizability)– Viscosity/rheology
In complex emulsions, interactions are often more important than the effect of individual components– Do not evaluate emollients in pure form only as this will give
incomplete information
Conclusions
© 2019 AAK Sweden ABNo part of this presentation may be reproduced in any form or by any means without the prior written permission of AAK Sweden AB. Disclaimer: This presentation is intended for educational purposes only. AAK Sweden AB shall not be liable for any third-party claims or losses of any nature, including, but not limited to, lost profits, punitive or consequential damages.
20