Lecture 4 - Moisturizers and Moisturization Flashcards
characteristics of normal skin vs. dry skin
Normal -Even texture and tone -Smooth surface -Supple plump feel -Free of irritation Dry -Rough & scaly surface -Flaky , large squames -Tight feel -Inflamed , red , blotchy, itchy
external factors of dry skin
- Low relative humidity in dry environments- winter , airplane
- Wind and air currents causing evaporation
- Soap & detergent stripping skin lipids
- Solvents – alcohol , acetone strip lipids
- Inflammation caused by UVR (ultraviolet radiation)
intrinsic factors of dry skin
- Impaired SC function
- Reduced sebum production
(eg. in aging skin) - Dietary deficiency of EFA (essential fatty acids- PUFA –polyunsaturated FA)
What 3 things happen with impaired SC function?
- Increased TEWL (trans epidermal water loss)
- Abnormal keratinization and desquammation
- Reduced levels of NMF (natural moisturizing factor)
top 5 causes of dry, dehydrated skin (according to alpha keri)
- Aging
- Over-cleansing (excessive bathing, scrubbing, use of soap)
- Extreme climatic conditions
- Prolonged sun exposure
- Lifestyle (poor diet, nutritional deficiencies, certain medical conditions and medications)
parameters to formulate effective moisturizers
- Key ingredients: emollients, occlusive agents, humectants
- Vehicle type: o/w, w/o emulsions, lamellar gel systems
- Ingredients are selected accordingly, depending on the vehicle type and the application target (face or body)
- Cosmetic forms: lotions, creams, oils, milks, serums, sprays, gels
- Targeted type of skin: normal, dry, sensitive, oily
- Marketing regimen: facial, hands and body
define emollients
provide partial occlusion that soothes, moisturizes and improves the appearance of the SC by masking the rough, scaly skin condition and reducing the sensation of itching
define occlusive agents
form a film on the surface of the skin and moisturize by retarding the evaporation of water (TEWL) from the skin surface
define humectants
bind water from the environment and help by retaining water in equilibrium within the skin
define enhancers of skin barrier
mimic the SC bilayers structure and assure long-lasting moisturization
What are emollients vs. moisturizers
Emollients -Lubrication -Skin “smoothing” & softening -Effect skin feel Moisturizers -Water retention -Humectancy -Barrier activity-Reduce water loss
Characteristics of emollients - physical forms (4 types)
- varying viscosity liquids
- soft solids - butters
- waxes
- cationic fatty compounds
5 categories of ingredients in emollients
Silicones Triglycerides Esters Hydrocarbons Ethers
9 criteria of selecting emollient esters and occlusive ingredients
- Chemical structure
- Polarity( Solubility Parameter)
- Spreading behavior
- Molecular weight
- Viscosity
- Hydrolytic stability
- Solubilizing behavior towards oil-soluble solids
- Permeability into skin
- Moisture retention
type of spreading with high mw esters vs low mw esters
— High MW esters deliver low spreading
— Low MW esters deliver high spreading
type of spreading with high visc vs low visc
- low visc = high spreading
- high visc = low spreading
Spreading values provide information about the_____ of an emollient
fatty character (alkyl chain portion)
types of hydrocarbon emollients
Mineral Oil-most popular PAOs Polyisobutenes Isoparaffins Petrolatum Paraffin, ozokerite & microcrystalline waxes Squalane – natural derived
Pros/cons of mineral oil
Pluses
- Most ubiquitous emollient-most common viscosity is 70 vis.
- More than a century of common use-internally & externally
- Inexpensive
Minuses
- Anti-mineral Oil attitudes - “clogs pores”, “de-fats the skin”, dermatologists
- No “Oil Free” Claims
define fixed oils
liquid triglycerides – fatty acid storage in oil seeds
define butters & fats
semi-solid triglycerides – usually melting above or near ambient temperature
define waxes
distinctly solid lipids primarily fatty acid esters (& also used to describe hydrogenated oils that have elevated melting points)
lanolin (unique emollient/emulsifier)
- Classified as a wax – composed of alcohol & sterol esters – “wool wax”
- Absorbs and retains high levels of water
- Self emulsifying W/O base – standardized by water absorption method
- Issues with animal origin and potential residual pesticides
4 other naturally derived emollients
CCT ( Capric/Caprylic Triglyceride)
Squalane
Jojoba Wax & hydrogenation
Myristyl Myristate
how is an ester formed
from reaction between an fatty acid and a fatty alcohol
Undergo hydrolysis at extreme pH’s (high or low) and elevated temperature
define spreading coefficient (S) of a liquid
determines how well that liquid will wet the surface (skin) when is applied
Spreading characteristic of an ester is dependent on its (what 3 things)
— chemical structure
— molecular weight (MW)
— viscosity
Chemical structure of an ester dictates the initial feel - how?
— Linear or unbranched esters tend to enhance slip or lubricity and can be heavy
— Branched chain esters tend to have a dry initial feel and spread easily
define spreading value
Surface area (mm2) covered in a specific time by the emollient (in vivo – human skin forearm, in vitro – VitroSkin etc.)
name very high spreading esters with a light, dry after - feel
— Diiso.propyl Adipate — Di-butyl Adipate — Hexyl Laurate — Isopropyl Myristate — Isopropyl Palmitate — Isopropyl Isostearate
name high spreading esters with an elegant/velvety after feel
— Tridecyl Neopentanoate
— Isostearyl Neopentanoate
— Isodecyl Neopentanoate
name medium spreading esters with medium after feel
— Isocetyl Stearate
— Cetearyl Isononanoate
silicones (general)
Silicone is a generic name for many classes of organo-silicone polymers with repeating siloxane (Si-0) units
Have a wide range of MW
silicone structure can be…
Cyclic, linear and cross-linked
Volatile or non-volatile
Silicone fluids are used because
- Are very resistant to high temperatures
- Very resistant to oxidation
- Are easily spreadable forming “breathable” films
- Good detackifiers reducing tackiness
types of hydrophilic emollients
Water soluble polymers & waxes- i.e.PEGs
Silicone copolyols
PEG esters
Ethoxylated alcohols & naturals (lanolin)
characteristics of humectants
- Attract and retain water- Hygroscopic
- Hydrogen bonding groups – Hydroxyl groups
- Act as freeze point depressants
- Act as skin moisturizers depending on RH
- Maintain an equilibrium with water vapor in air
characteristics of glycerol
- The most common used humectant in personal care — Used between 2-25% in moisturizers to treat dry skin - Heavy and tacky feel — Excellent skin tolerability ; — Low cost — Help wound healing in skin — Desquamation — Skin barrier recovery - Anti-irritant
characteristics of Pyrrolidone Carboxylic Acid
Sodium PCA- “Natural Moisturizing factor”NMF
Found in the skin
Extremely Hygroscopic
Extremely safe, even at high conc.
Very stable to broad range of pH and temp
characteristics of hyaluronic acid
Glycosaminoglycan
The most efficient “moisturizer”
Ubiquitous to humans- connective tissue, vitreous fluid of eyes,dermis
Most commonly used material made from bacterial fermentation
Medical grades also from Rooster combs
Film former/ retains water
types of Moisturization Efficacy Testing
Trained graders: dry flaky skin
D-Squame tape grading- SC flakes
Conductivity & Impedance meters (NOVA Meter, Skicon Corneometer )
TEWL (Trans Epidermal Water Loss)
Macrophotography- grading before & after
Skin replicas- image analysis
types of Bioengineering Instrumentation
Moisture testing – direct and indirect –TEWL
Skin Friction – hydrated skin > dry skin
Skin Elasticity Resiliency- Cutometer, Twistometer, Ballistometer
Skin pH • Skin surface temperature IR scan
Sebumeter- surface oil by light diffraction
Skin tone – Chromameter ( L,a,b values)
Laser Doppler blood flow- erythema, vasodilation
Skin Topography- Profilometry-wrinkle number, length, depth (“reduces fine lines”)
Image Analysis – direct/ indirect replicas
Microscopy: Light, Con-focal, SEM
moisturizers treat dry skin rehydrate and restore the skin barrier by using…
— Occlusive agents which seal skin to prevent water loss
— Emollients provide semi-occlusive films; also act as plasticizers and feel modifiers
— Humectants attract and hold water (similar to NMF)
— Enhancers of skin barrier to replenish damaged lipids and reinforce the skin’s natural lipid barrier function
