How to Stability Test your Cosmetic Products

Before you submit a cosmetic product for a CPSR it is necessary to have an idea of shelf life and to have performed a stability test. 

The following information is based on UK cosmetic making, but those of you around the world making cosmetics, I'd highly recommend stability testing your products.  It's easy to do and gives you the peace of mind that what you are sending out to your customers is stable for use.

You can do this yourself or have a lab perform the tests for you.

If your product is aqueous and being sent to a lab for challenge testing anyway, it may be convenient to simply send them more samples so that they can also perform the stability test for you too.

If you choose to do stability testing at home then you can do it two ways.

• Observe your product for 12 months at room temperature.

OR

• Perform the Freeze Thaw Stability test.

I’d actually opt for both if possible, but definitely, if not sending to a lab, perform the freeze thaw test.

The freeze thaw stability test was designed to ensure that products remain stable at drastic and sudden temperature changes.  This is because during transit in different parts of the country (and world) the storage temperatures and weather can change meaning that during its shipping journey a product can be exposed to many fluctuating temperatures.  This can affect the product.  This test is designed to check if it does and to what degree.

It was advised to be that if performing this test at home then a cycle such at below is sufficient:

• Retain a sample of your product at room temperature as your control sample.
• Freeze 3 more of your products in the finished container/packaging for 24 hours
• Remove from freezer and leave at room temperature to thaw for 24 hours.
• Repeat 3 times and note changes in colour, smell, texture, and PH if an aqueous product, each time.

If no change on the final 24-hour thaw then you can assume that your product is stable for the maximum of 6 months shelf life.

NOTE:  Doing this twice will not give you a 12 months shelf life.  To achieve this you need to observe for 12 months real time or submit to a lab for an accelerated test.

However, if you read journals on this method, they suggest an additional step.  The reason it is not suggested to small cosmetics businesses is that often it is impractical to be able to heat the product for that long and safety is a concern.  This is a benefit of sending your product to a lab, as they can do this safety.  The process is:

• Retain a sample of your product at room temperature as your control sample.
• Freeze 3 more of your products in the finished container/packaging for 24 hours
• Remove from freezer and leave at room temperature to thaw for 24 hours.
• Put samples in an over at 50 degrees C for 24 hours.
• Remove samples and allow to come back to room temperature.
• Repeat 3 times and note changes as stated above.

As you can see, putting a product (likely contained in a plastic container) in an over for 24 hours is not only unsafe in a home or small business premises environment, but also expensive to keep your oven on for that length of time, especially when repeating it 3 times.

I would advise to stick with the simple freeze thaw method, as I have been told by a lab that this is acceptable. 

If you want a shelf life of more than 6 months, then either observe your products at room temperature for 12 months in addition to the freeze thaw, or send samples to a lab to do accelerated testing.   Accelerated testing usually takes around 3 months for a 12-month shelf life, assuming that the product is stable.

What if I notice changes?

Draw yourself up a table a bit like the one below, that we’ve drawn as an example. 

Record your data for your control sample and then each time your product has finished one freeze thaw cycle. 

It may not have changed at all, or it may have changed slightly. 

If you notice significant changes after the first and second cycles then I would advise revisiting your formula and looking at what might have caused those changes.  For example, if an anhydrous product smells a bit off, then did you remember to add an antioxidant?  Has the colour or texture changed?  Did you check if any of your ingredients were unstable at certain temperatures? 

You want to ensure that your product is safe for use.  Remember that your CPSR assessment only checks your recipe and any contraindications.  They do not sample your product unless challenge testing, you must ensure your stability testing is truthful and accurate.

Whatever stability testing you do, always keep a sample with the batch number and date stored at your lab.  It’s good to observe samples of everything you make to ensure that they are performing as expected.  By doing this you can notice any changes in batches as they happen, they may be down to an ingredient, a manufacturing error or anything else.  The safety of your customers is paramount.

Disclaimer: I am not a qualified cosmetic chemist.  I am self taught and offer up any information based on my own knowledge and experience, I take no responsibility for how you use this information.  The information that I do give is based on much research and confirming with qualified individuals.  Most of the information given is valid in the UK, so if you live elsewhere check your own countries cosmetic regulations for guidance.