The Stability and Packaging Compatibility Test is an essential laboratory test for cosmetic products. This test evaluates whether a cosmetic formulation remains stable during the intended 12-month shelf life and whether the packaging is compatible with the formulation.

During this test, the product is exposed to controlled conditions for an accelerated testing period of 4 weeks. Based on this accelerated stability test, a scientifically supported estimation can be made regarding the product’s stability during 12 months of storage under normal conditions.

The test is performed according to ISO 18811:2018, the international standard for stability testing of cosmetic products.

This is a shortened stability test designed to support a 12-month shelf life indication on the product label. The standard shelf life test is: Stability and Packaging Compatibility Laboratory Test.

Why Stability Testing Is Important

Cosmetic products must remain safe, effective, and stable throughout their entire shelf life. Instability can lead to:

• discoloration of the product

• odor changes

• phase separation in emulsions

• viscosity changes

• loss of ingredient effectiveness

• interaction with the packaging

In addition, incompatible packaging may lead to:

• deformation or discoloration of the packaging

• migration of substances from packaging into the product

• leakage or packaging damage

• malfunction of pumps or dispensing systems

Stability testing helps detect these issues at an early stage, before the product is placed 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:

• Minimum durability date (Best Before)

• PAO – Period After Opening

Which of these must be used depends on the demonstrated stability of the product.

1. Product With a Stability of 12 Months

If stability testing demonstrates that the product remains stable for at least 12 months but less than 30 months, the label must include a minimum durability date.

This is usually displayed using the hourglass symbol.

Example on the label:

Best before: 06/2027
or
Best before end: 06/2027

This means the product remains stable until that date when unopened.

In this situation, a PAO symbol is usually not required, because the shelf life is already defined by a specific date.

2. Product With Stability of 30 Months or More

If stability testing demonstrates that a product remains stable for at least 30 months, the label does not require a best-before date.

Instead, the product must display a PAO symbol (Period After Opening).

This is the well-known open jar symbol with a number of months.

Example:

12M
24M

This means the product can be safely used for 12 or 24 months after opening.

Shelf Life Differences on Product Labels

Practical Differences for Cosmetic Brands

12 Month Stability

Advantages

• shorter test duration

• often sufficient for niche or small-batch products

Disadvantages

• best before date required on the label

• less flexible logistics

• some retailers do not accept short shelf life products

30 Month Stability

Advantages

• no best before date required

• only PAO symbol needed

• easier stock management

• preferred for retail and export

Disadvantages

• longer stability testing required

What Is Tested

During the stability test, several aspects of the cosmetic product are evaluated.

Physical Stability

The product is checked to ensure it retains its original properties, including:

• color

• odor

• appearance

• texture

• viscosity

• phase stability

Chemical Stability

The formulation is evaluated for possible changes or degradation of ingredients.

Packaging Compatibility

The product is tested in its commercial packaging to determine whether interactions occur between the formulation and the packaging.

The following aspects are evaluated:

• deformation of packaging

• discoloration of packaging or product

• leakage

• compatibility with pumps or closures

• possible migration effects

Test 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. Observations and measurements are performed at defined intervals during the testing period.

The evaluation includes:

• visual inspection

• physical assessment of the product

• inspection of packaging and closures

• documentation of any changes

All observations are recorded in a detailed laboratory report.

Photo Documentation of the Test

During the stability test, photos of the samples are taken at different stages of the testing period.

This photo documentation:

• visually demonstrates any changes

• supports the stability assessment

• can be included in the Product Information File (PIF)

• provides additional transparency for quality control

The photos are included in the final test report.

Test Duration

Total test duration: 4 weeks

This accelerated stability test provides an indication of 12 months shelf life under normal storage conditions.

Required Samples

To perform the test, the following samples are required:

• 200 ml or 200 g of product and

• 6 units in the final packaging in which the product will be marketed

It is important that the packaging submitted is identical to the packaging used for the final product on the market.

Suitable Products

The stability test can be performed for nearly all types of cosmetic products, including:

• creams and lotions

• serums

• shampoos and conditioners

• gels and toners

• scrubs

• liquid soaps

• oils

• emulsions

When Is a Stability Test Needed

A stability test is commonly performed in the following situations:

• during development of a new cosmetic product

• when introducing new packaging

• when modifying the formulation

• when extending the shelf life

• as part of the Product Information File (PIF)

Although the EU Cosmetic Regulation does not prescribe a specific test, the manufacturer must provide evidence that the product remains stable throughout the indicated shelf life.

A stability test according to ISO 18811 is a widely used and reliable method to demonstrate this.

Test Results

After completion of the test, you will receive a laboratory report containing:

• 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 regarding 12-month shelf life stability

This report can be used as part of the cosmetic product documentation, including the Product Information File (PIF) and the Cosmetic Product Safety Report (CPSR).