With such a vast array of materials to choose from, an increasingly competitive market place and consumer expected shelf lives of up to 3 years, it can be challenging to select the right materials for a product formulation to ensure efficacy, aesthetics AND stability. What fundamental steps can you take to foolproof your formulations to ensure they achieve the required shelf life?
Foolproof check # 1: Is the pH right for the product and all of its ingredients?
When something goes wrong with a formula, incompatibilities with pH is by far the most common issue. If the pH of the finished product is not compatible with the preservatives, actives or any other functional ingredients used for that matter, the formula’s efficacy or shelf life will be affected. Remember too that pH will drift over the shelf life of the product – it is not uncommon for a pH drift of up to +/-10% over the shelf life of a product, and sometimes up to +/-20%! This means that a product pH adjusted to 5.0 could realistically have a pH drift to 4.5 – 5.5 over its shelf life, or even up to a range of 4 – 6! All ingredients, especially the preservatives and active ingredients used, would therefore need to be compatible in this broader pH environment, to ensure the formula will be stable and effective throughout its shelf life.
Foolproof check # 2: Is the method suitable for scale up?
The right materials put together the wrong way can yield a very unsatisfactory result. Make sure materials are put together even in lab size samples using the correct method and in a way that can be scaled up to larger machinery. If you are having trouble stabilising a small sample in the lab, then chances are it will be very difficult to hold together in a 200kg+ batch… so make sure methods are translatable to the size of batch you want to scale the product up to. Common problems we see are issues with achieving the required temperatures without impacting on some ingredients (and cooling extremely hot products down on a large scale can also be very problematic) and using the incorrect shear. For example, some materials are shear sensitive – which means they should never be exposed to high shear. Has this correctly been written into the method to ensure a mistake does not occur on scale up? If a material requires very high shear in the lab, can this shear then be translated in sufficient rpm to suit very large batches? Make sure your method very clearly states required temperatures and high/low shear as required so that scale up can be performed according to the batch size and machinery used. Not sure which materials require which type of processing? Then get the knowledge to be confident with the methods you write into your formulations!
Foolproof check # 3: Have stability enhancing factors been incorporated?
This can be simple things like using a suitable gum/polymer for the continuous phase or using antioxidants wherever vegetable or essential oils are used (and some actives). It would commonly mean using suitable emulsifier blends to stabilise emulsions or surfactant blends to support foam while enhancing mildness. It could mean double checking all actives to see if anti-oxidants and/or chelating agents or other stability enhancing materials need to be incorporated. Either way, you need to double check all formulas in theory before proceeding to sample development to ensure they incorporate the right type of stabilising ingredients for the ingredients used and form required. If you aren’t sure what stabilising methods should be incorporated into a formulation, then get the training to fill in those gaps of knowledge to make sure you do – bad theory translates to bad samples and poor stability which is never a good thing!
One last very important point!
Don’t forget that even the best theory can yield a very different result in the lab. Remember to plan for and conduct suitable accelerated stability testing before releasing product into the market to prevent product failing and a dreaded product recall. The investment in stability testing is cheap compared to a product recall! If selling in EU, it is a requirement that you can support shelf life, and this can only be done through accelerated and real time testing. Get your products stability tested before launching or learn how to conduct the stability testing yourself for peace of mind.