Stability testing can be done on the formula on its own or on the formula in its container (primary packaging). It is generally conducted under accelerated aging conditions.
For each stability test, you should provide to your Responsible Person:
- The results with the test conditions and the different variables.
- The conclusions of the test including the extrapolation under normal conditions.
NB: If you have a base formula and different color variations, it is your responsibility to determine whether you need to test each color variation or if the testing done on the base formula can be extrapolated to the shades.
Physical & Chemical:
These tests are commonly used to predict the resistance of the cosmetic product to extreme conditions e.g. high and low temperature, light, etc.
The high-temperature used to perform this test is usually between 37°C to 45°C for three months. The product also needs to be subjected to low temperature for three months, usually at -10°C.
A lot of companies choose to test their product at 40°C because most products will show excellent stability. Over 45°C, if the product contains oils and fatty alcohols, it can be affected and the results will be less accurate.
The threemonth period allows the assessor to conclude on the stability of the product for a period of thirty months.
The product must be tested during three cycles of temperature testing. Repeat this test three times. One cycle corresponds to:
- 24 hours at -10°C
- 24 hours at 25°C (room temperature)
You can also provide a more rigorous testing which needs to be done in 5 cycles:
- 24 hours at -10°C
- 24 hours at 45°C (room temperature)
The centrifuge testing allows you to check the creaming. When an emulsion product is made with oil in water, it has the tendency to separate and rise to the top. To verify and avoid such trouble, heat the emulsion to 50°C and centrifuge it for thirty minutes at 3000 rpm. Then inspect the resulting product for signs of creaming. This is highly important essentially for products that contain powders of any kind such as liquid cream or liquid make-up.
Mechanical shock testing:
Sometimes products can be damaged during transportation/shipping. To avoid a commercial disaster, you can use a pallet shaker to determine if your formula could be affected by shipment.
To control the light stability you must perform one test by exposing your product to daylight during 6 months. To assess the stability you should report your observation on day 1, 3, 8, 2 weeks after, on the first, second and third months and finally 6 months after the beginning of the light testing.
You must also perform a test with mercury vapor UV lamps to accelerate the phenomenon. It allows to assess sun resistance. For the stability of your product during the sun test you should draw your conclusion after 30 min, 1,2,4,6 and 8 hours after the beginning of the test.
Parameter variability during product shelf life:
To draw your conclusions on the stability of your products you must look out for the appearance, the odor, the PH, the viscosity, weight changes, microbial tests demonstrating the ability of the products to prohibit microbial growth during normal use and other specific tests if necessary, and, analytical data in relation to other parameters for specific product types.
You must ensure the quality of microbiological flora of your cosmetic product by providing tests. You can either realize screening tests by yourself with a specific kit sold on the market or quantitative tests by a laboratory that will ensure the microbial safety of the cosmetics.
Stability testing should include packaging, which is made of exactly the same material(s) and is as similar as possible in all other respects to the packaging in which the product will be marketed. If the product is marketed in several different package types, it is advisable to study each package type. Where there is a range of package sizes, it is advisable to test the product in the smallest container. Appropriate controls (for example, product in glass containers) should be used. It may also be advisable to test the packaged product in various positions (upright, inverted, on its side, etc.)
Date of Minimum Durability (DoMD)
Cosmetic products must indicate when they are best used by or how long they should be kept.
The date of minimum durability called “DoMD” must be clearly expressed and preceded by the mention "best used before the end of". You can avoid the wording by using the hour-glass symbol as suggested by Annex VII of the cosmetic regulation.
The date consists either of the month and year (MMYYYY or MMYY) or the day, month and year DDMMYYYY or DDMMYY)
The DoMD determination of each product must be based on stability tests under accelerated or normal conditions. If this determination comes from the stability tests under accelerated conditions, the results must be extrapolated for the stability under normal conditions (i.e. a conclusion regarding the DMD of each product is awaiting)
NB:For some products, there's no need to indicate the DoMD e.g. single use products, aerosols, perfume, etc.
If the DOMD is equal or less than 30 months, you should stick with the DOMD on your pack. However, if the product shows very good stability with a DOMD over 30 months, then you must indicate the Period After Opening (PAO) on your product (see below) symbolized by the open-jar symbol. The determination of the PAO depends on the results of the Challenge test.
The challenge test must be carried out in accordance with the standard ISO 11930 or with the European pharmaceutical standards. You can also use other standards such as USP 51 as long as you add a measure at Day 7.
This test must include:
- Identification of the sample tested: name, batch number
- Information on sampling: quantity used in the sample, the temperature of the packaging, the beginning of the analysis, the results obtained
- Test methods: evaluation of antimicrobial preservation of the sample
- Interpretation and the acceptance criteria
- Approval and signature.
If you do not perform a challenge test, then you need to scientifically justify your decision. Using the ISO 29621 norm can be a way to waive challenge testing for certain products.
Microbiologically low-risk products (ISO 29621):
In limited cases there’s no need to conduct a challenge test. Indeed, the likelihood of microbiological contamination for some cosmetic products is extremely low (or non-existent) due to product characteristics that create a hostile environment for survival/growth of microorganisms. These characteristics are elaborated in this International Standard ISO 29621.
- Single use product
- Low water activity (aw): anhydrous minerals powders
- pH of formulation (pH > 10 or pH < 3.5)
- Products with high alcohol content such as perfumes ( ~ > 20 %)
- Raw Materials that create a hostile environment
- The type of packaging (pump dispenser, airless container)
Period After Opening (PAO)
The Period After Opening (PAO) symbolized by the open-jar symbol must be placed on the label of your cosmetic product when the Date of Minimum Durability is over 30 months.
The PAO helps to identify the shelf life of a cosmetic product after it has been opened. The symbol is easily understandable by the consumer: it represents an open cosmetic jar with a number of months or years, written either inside or outside the jar.
This requirement is set by the European Cosmetic Regulation 1223/2009 in Annex VII point 2. The duration notation is commonly set by norm ISO 8601.
The PAO determination is based on the synthesis of all available information on the product, for example, the results of the challenge test, stability test, normal or reasonably foreseeable conditions of storage, the historical data, qualitative and quantitative data, etc.
There is no standard for the determination of the PAO. Usually, the formulator is able to provide this information but the common criteria are:
- Result of the challenge test
- Formula and process: % of water & solvent, nutrients, pH
- Packaging: contact product/packaging, volume/dose/frequency of use
- Function and conditions of use: rinse-off, leave-on
- Type of users: adult, children, infant or elderly
- Area of application: small, medium, large
- Specific risks: storage products, travelling products, extemporaneous
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