Why:To ensure that the cosmetic product maintains its intended physical, chemical and microbiological quality, as well as functionality and aesthetics when stored under appropriate conditions.
When: The most common conditions for stability testing of cosmetic products are listed in several published references:
(✓) International Federation of Societies of Cosmetic Chemists, IFSCC Monograph, Number 2 (The Fundamentals of Stability Testing):
|Room Temp||20 – 25° C||–||Shelf life|
|Accelerated||37° C||–||3-6 months|
|Accelerated||37° C||80%||1 month|
|Accelerated||45° C||1-3 months|
(✓) Cosmetic Regulation in a Competitive Environment(Ch 11 “Stability Testing of Cosmetic Products”)
|Accelerated testing:||37, 45 and 50°C|
|Freeze-thaw cycling:||0 or -5°C|
|Elevated humidity:||80% RH|
How: Stability testing is an experiment in which samples of the formula are put at different environmental/ storage conditions for a set period of time to simulate what will happen to the product during its life cycle. At selected intervals, samples are evaluated for various physical, chemical and performance characteristics to see if and how they have changed.
- Selection of batches:
It is recommended to use at least one batch of the cosmetic product, the same batch as the marketed product.
- Container/ Closure system:
The container/closure system(s) shall be the same as the one used when placing the product on the market. Any other studies carried out on the cosmetic product outside its immediate container or in other packaging materials can form a useful part of the stress testing of the cosmetic product or can be considered as supporting information, respectively.
Appropriate controls (for example, product in glass containers) should be used.
- Stability evaluation parameters:
- Organoleptical properties: color, odor and appearance,
- Physico-chemical properties: pH value, viscosity, density, the monitoring of fomulation ingredients (whenever applicable)
- Microbiological stability: microbial count & Challenge Test of the preserving system made before and/or after the Accelerated Stability Test.
- The compatibility between the content & the container (Compatibility Test)
- Analytical data in relation to other parameters for specific product type
A preliminary test recommended is the centrifugation test. This test predicts emulsion creaming (for powder, liquid/cream products).
• A sample heated to 50°C is centrifuged at 3,000rpm for 30 minutes.
(✓) The product must remain stable and any sign of instability shows the need for reformulation.
If approved in this test, the product can then be submitted to the stability tests.
Preliminary stability test – it is also known as Screening test, Accelerated stability test or Short term test.
Why: help in the screening of the formulation.
When: is carried out in the initial phase of product development.
How: the samples can be submitted to:
- heating in ovens,
- cooling in refrigerators,
- to alternate cooling and heating cycles.
Duration of the study: 15 days
The parameters to be evaluated:
- Organoleptic characteristics: appearance, color, odor and flavor, whenever applicable.
- Physical-chemical characteristics: pH value, viscosity, density, or others.
Accelerated Stability Test
An accelerated stability test is also a possibility, none the less, the product will be required to be submitted to more-severe-than-usual conditions.
The accelerated stability is also known as normal or exploratory stability test. This test is a predictive study that can be used to estimate the expiry date of the product.
Duration of the study: generally 90 days.