Stability Test and Compatibility Test - 12 Months Shelf Life
The Stability and Compatibility Test is an essential laboratory test for cosmetic products. This test assesses whether a cosmetic product remains stable for its intended shelf life of 12 months and whether the packaging is compatible with the formulation.
During this test, the product is exposed to controlled conditions for an accelerated test period of 4 weeks. Based on this accelerated stability test, a scientifically based estimate can be made of the stability of the product during 12 months of storage under normal conditions.
This test is conducted according to ISO 18811:2018, the international standard for stability testing of cosmetic products.
This is an abbreviated test for a 12 Month Shelf Life indication on the product label. The standard shelf life test is: Stability Test and Compatibility Test Laboratory
Why stability testing is important
Cosmetic products must remain safe, effective and stable throughout their shelf life. Instability can lead to:
- discoloration of the product
- odor change
- phase separation in emulsions
- change in viscosity
- loss of efficacy of ingredients
- interaction with packaging
In addition, incompatible packaging can lead to:
- deformation or discoloration of the packaging
- migration of substances from the packaging to the product
- leakage or damage to packaging
- deterioration of pumping or dispensing systems
With a stability test, these problems can be detected early, even before the product is launched on the market.
Shelf life according to the EU Cosmetic Regulation
According to Article 19 of the EU Cosmetic Regulation (1223/2009), the shelf life of a cosmetic product must be indicated in one of two ways:
- Date of minimum shelf life (Best before)
- PAO – Period After Opening
Which of these two is used depends on the stability of the product.
1. Product with stability of 12 months
If a stability test shows that the product remains stable for at least 12 months, but not more than 30 months, the label must include a date of minimum shelf life.
This is usually represented by the hourglass symbol.
Example on the label:
- Best before: 06/2027
- Or: Best before end: 06/2027
This means that the product will remain stable unopened until that date.
In this case, a PAO symbol is usually not required because the shelf life is already indicated by a specific date.
2. Product with stability of 30 months or longer
When stability tests show that a product remains stable for at least 30 months, there is no need for a best before date on the label.
Instead, the product must have a PAO (Period After Opening) symbol.
This is the familiar open pot symbol with a number of months.
Example:
- 12M
- 24M
This means that the product can be used safely for 12 or 24 months after opening.
Difference shelf life on product label
| Stability demonstrated | Label requirement | Symbol |
|---|---|---|
| < 30 months (e.g., 12 months) | Best before date required | Hourglass |
| ≥ 30 months | No best before needed | PAO symbol |
Practical difference for cosmetic brands
12 months of stability
Benefits:
- shorter test possible
- often sufficient for niche products
Disadvantages:
- best before date required on label
- logistically less flexible
- retailers sometimes do not accept a short shelf life
30 months of stability
Benefits:
- no best before date needed
- PAO symbol only
- easier inventory management
- better for exports and retail
Disadvantages:
- longer stability test needed
What is being tested
During the stability test, different aspects of the cosmetic product are analyzed.
Physical stability
It is verified that the product retains its original properties:
- color
- scent
- appearance
- texture
- viscosity
- phase stability
Chemical stability
The formulation is checked for possible changes or degradation of ingredients.
Packaging compatibility
The product is tested in the commercial package to assess whether product-package interactions occur.
Attention will be paid to:
- deformation of packaging
- discoloration of packaging or product
- leakage
- compatibility with pumping or locking mechanisms
- possible migration effects
Testing method according to ISO 18811:2018
The test is performed according to the international standard ISO 18811:2018 – Cosmetics – Stability testing.
During the test, samples are stored under controlled conditions to simulate accelerated aging. During the test period, observations and measurements are made at set times.
The evaluation includes:
- visual inspection
- physical assessment of the product
- control of packaging and sealing mechanisms
- documentation of any changes
All observations are recorded in a detailed laboratory report.
Photo documentation of the test
During the stability test, photographs of the samples are taken at different times during the test period.
This photo documentation:
- Shows visually if changes are occurring
- supports stability assessment
- may be included in the Product Information File (PIF)
- provides additional transparency for quality control
The photos are part of the final test report.
Test duration
Total duration of the test: 4 weeks
This accelerated stability test allows an indication of a 12-month shelf life under normal storage conditions.
Required samples
To perform the test, we need the following samples:
- 6 pieces in the final package in which the product will be sold
- and 200 ml or 200 g extra
It is important that the packaging be identical to that which will be used in the marketplace.
When is a stability test necessary
A stability test is often performed in the following situations:
- In the development of a new cosmetic product
- when new packaging is used
- when changing the wording
- upon extension of shelf life
- As part of the Product Information File (PIF)
Although the EU Cosmetic Regulation does not require a specific test, the manufacturer must have evidence that the product remains stable during the stated shelf life.
A stability test according to ISO 18811 is a widely used and reliable method for this purpose.
Result of the test
Upon completion of the test, you will receive a laboratory report with:
- description of the test method
- test conditions
- observations during the test period
- evaluation of product stability
- assessment of packaging compatibility
- photo documentation of the samples
- conclusion on stability for 12-month shelf life
This report can be used as part of cosmetics product documentation, such as the PIF and safety assessment (CPSR).
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