Evaluation of Creams and Powders
Evaluation
of creams
1. Rheological
properties /Viscosity
• The application behavior and long-term stability of skin
creams and lotions in both cosmetic and pharmaceutical applications are
important factors for the acceptance of the product by the consumer
• Rheological measurements ensure that the products feel and
behave on the skin as they should
• The rheological properties of creams and lotions are
largely influenced by the ingredients and by the manufacturing process
• The flow behavior of creams can be evaluated using
viscosity measurements
• To obtain consistence in quality, viscosity should be
measured during the manufacturing stage
• As soon as the ideal consistency of a cream has been
found, this consistency needs to be determined quantitatively and documented in
order to use this as a reference for later products
• Viscosity should remain constant throughout the shelf life
• Measured with Brookfield viscometer or Ford viscosity cup
/ Rheometer
• Cosmetic creams and lotions generally show shear-thinning
behavior.
• This means that the viscosity is not a constant value, but
depends on the shear intensity
Viscosity
v/s Rheology?????
Viscosity
• Viscosity is a measure of the resistance of fluid to an
applied stress
• In simple terms it is like the “thickness” of a fluid or
gas
• The measurement of viscosity is a simple test and the
result reported is generally a single number
• For the results of a viscosity test to be relevant, they
should be compared to the results of tests done at the same temperature
• It is normal for fluids to become more viscous at colder
temperatures and less viscous at higher temperatures
Rheology
• Rheology is a more complex study of the flow of matter;
mainly liquids, but also soft solids, gels, pastes and even sold materials that
exhibit some level of flow (ie. do not just deform elastically).
• Rheology applies to substances that have a complex
structure, including: muds, sludges, suspensions, polymers, petrochemicals and
biological materials.
• The flow of these complex materials cannot be
characterized by a single value of viscosity, instead viscosity changes with
changing conditions
• Ketchup’s viscosity lowers when it is shaken
• Cornflour’s viscosity increases when it is struck
• The difference between a viscometer and rheometer is
essentially the quality of components and control capabilities.
• Basically, a rheometer is more versatile and has a wider range of applications than a viscometer does.
The Ford viscosity cup is a simple gravity device that permits the timed flow of a known volume of liquid passing through an orifice located at the bottom.
2. Spreadability
testing
• Spreadability of gels, creams, ointments and lotions is
the net result of a combination of rheological parameters
• Lipid rich cream will have decreased spreadability values
with an increase in viscosity and surface tension (a measure of cohesiveness),
making the cream greasy, tacky and difficult to spread
• The lower the viscosity of a cream, the lower the surface tension and the more the cream is easily spread and absorbed into the skin.
3. Estimation of
active ingredients
• Chromatography
• Spectrophotometry
4. Sensitivity
testing (Patch test)
• To measure sensitization of skin
• Patch test is normally open or occlusive
• The test sample is applied along with a standard marketed preparation at different places of the skin and effect is compared after a period of time
5. Dermal irritation
testing
• Draize test carried out on rabbits
• A known amount of test substance is introduced under a one
square inch gauge patch
• The patch is applied to skin of 12 albino rabbits, (6 with
intact skin) and (6 with abraded skin)
• The patch is secured in place with adhesive tape and the
entire trunk of the animal is wrapped with an impervious material for a 24 hour
period
• After 24 hours the patches are removed and resulting
reaction is evaluated for erythema and edema formation.
• The reaction is again scored at the end of 72 hours and the two readings are averaged
6. Microbiology
testing for microbial counts and pathogens
• Preservative
Challenge Testing: involves the evaluation of antimicrobial efficacy of the
preservative system in accordance with the relevant international standards
• Total Viable Count:
Control of microbiological cleanliness
• For Antimicrobial Effectiveness Testing, a standardized
inoculum is mixed into the liquid product
• Inoculation with 3 bacteria (Staphylococcus aureus, E.
coli, and Pseudomonas aeruginosa), a yeast (Candida albicans) and a mold
(Aspergillus brasiliensis – formerly known as Aspergillus niger)
• At designated time points, aliquots of the inoculated
product are plated to determine the number of microorganisms surviving in the
product
• These microorganisms, the designated time points,
pass/fail criteria and test category of the product are usually determined by
official compendia such as USP and the European Pharmacopoeia
7. Visual test
For homogeneity of drug product may be useful, at least for
an exhibit batch, to ensure no separation of phases, no synersis (extrusion of
water from a gel), and no foreign matter
- In addition, if test drug product contains a dispersion of
drug substance, number of crystals per ten fields of microscopic view is useful
to ensure product quality.
8. pH
Potentially affects the stability of the drug substance and
physicochemical properties of semi-solid products (e.g., emulsion stability,
rheological behavior)
- pH also may affect effectiveness of the preservatives and
viscosity of the drug product
- pH is measured with a pH meter
Efficacy
testing of skin products
• The human “guinea pig” is the most relevant species on
which consumer products can be evaluated
• In functional terms, the human skin, teeth or nails will
be the ultimate substrates on which a novel product will have to prove its
performance
• Psychologically, the human user will be the ultimate judge
of how well a product works
Testing of skin
products on artificial skin
• A UK-based laboratory is working to eradicate animal
testing in the cosmetics industry by developing alternative methods which are
not only cruelty-free but more scientifically advanced than other current tests
• XCellR8 uses scaffolds of cells from human skin donated by
plastic surgery patients, which they say are ideally suited to testing cosmetic
products
• If a cross section of the artificial piece of skin is
taken, it is almost identical to real skin on the body
• It even has a skin barrier so you can apply full cosmetic
formulations to the surface.
• These skin models are incubated with samples of cosmetic products or ingredients at assess how much damage is being done to the skin over a period of time
L’Oreal will use the artificial skin developed by the
startup company startup Organovo to test cosmetics, significantly reducing
costs associated with the testing process and improving the speed at which
products hit the market
• Health and Family Welfare Ministry of India has amended the Rule 135-B which now states that, “Prohibition of import of cosmetics tested on animals. No cosmetic that has been tested on animals after the commencement of Drugs and Cosmetics (Fifth Amendment) Rules, 2014 shall be imported into the country”,
SAFETY
ASSESSMENT FOR COSMETICS
The safety assessment is part of a package of information,
which the manufacturer or importer must keep up-to-date and available for
inspection by the Authorities
a) Composition of the cosmetic product
b) Physico-chemical and microbiological specifications of
raw materials and finished product
c) Method of manufacture
c) Method of manufacture
d) Cosmetic safety assessment, and details of the safety
assessor
e) Existing data on the undesirable effects on human health
(eg .from customer complaints)
f) Proof of the effect (only for certain products, such as
sunscreens)
g) Data on animal testing performed by the manufacturer, his
agents, or suppliers relating to the development or safety evaluation of the
product or its ingredients
Summary
Evaluation of Creams
• Viscosity
• Patch testing
• Spreadability
• Dermal irritation
• Microbiological testing
• Estimation of active ingredients
Evaluation of Face
powders
• Shade control
• Dispersion of colour
• Pay off
• Drop test
• Microbiological testing
• Penetration test
• Bulk density
• Efficacy testing
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