Cosmetic emulsions with stability problems: what is the cause?

Emulsion stability problem 1: colour and aroma changes in your cream or lotion.

When you have colour or aroma changes in your cream or lotion formula, you’ll need to determine if the colour or aroma change is sufficient enough to impact the enjoyment by your consumer. You will also need to check if the colour or aroma change impacts the safety and efficacy of the product. A slight aromatic difference or tint of colour may be acceptable by a consumer, but if the pH or viscosity is adversely affected, then the product is considered unstable.

Try these fix-its to improve the colour and aromatic stability of your emulsion formula:

• add a small input of chelating agent and see if this restores the original colour. Find out about chelating agents here. If it does, you will need to add chelating agent to your formula, and all future batches.
• try preparing another sample with a little more or less antioxidant and see if that reduces colour and aromatic changes. Read this blog to see how vitamin E can have a pro-oxidant effect in cosmetic formulas, and watch this video to see how to test if you are using the right input.
• Conduct microbial checks to ensure there is no microbial contamination of your cosmetic formula, and to confirm the input of preservative is sufficient.

Emulsion stability problem 2: your emulsion shows separation.

Oil in water emulsion formulas will show partial or fully separated layers when there is either:

• too much oil for the emulsifiers and/or other stabilizing agents such as gums or polymers to hold the oil droplets homogenous
• a significant pH change, which causes the emulsifiers or stabilizing agents to become ineffective

To investigate and potentially fix the problem, start by taking the pH of your failed sample. If it has changed dramatically, then investigate why that change occurred; often it has to do with oxidation or some other incompatibility, such as electrolytes. If you can fix the original cause, you will then stop the large shift in pH which caused the instability. Watch how to check and measure pH here.

If the pH of the failed sample is within an acceptable range but there is still separation, then it is most likely the ratio of oils to emulsifiers you have used. Increase your emulsifiers and stabilizing agents such as gums or polymers in your formula, or reduce the oil input and prepare another sample then test its’ stability.

 

Emulsion stability problem 3: your cream or lotion looks grainy or waxy.

A waxy or grainy appearance to your emulsion can sometimes happen quite quickly after it has first been made. In these cases, it is usually due to waxes not being sufficiently heated while the emulsion is being formed, so that very fine waxy particles ‘set’ before they can be incorporated homogenously into the micelles of an emulsion. If this is the case, the cream or lotion will have a very limited shelf life, and will tend to separate before much longer.

To fix this problem, you will need to make a new sample and ensure the oil and water phases are both sufficiently heated above the melting point of the waxes used, so that the micelles of the emulsion can form while both phases are liquid before cooling starts.

Another reason for a grainy or waxy appearance, particularly if it does not occur straight away, can be due to crystallization in the emulsion. This can only occur when an ionic emulsifier has been used, such as an anionic emulsifier in a cream or lotion, or a cationic emulsifier in a conditioner. For crystallization to occur, it means that too much ionic emulsifier has been used in the formula to tolerate a low temperature. To fix this problem, create a new sample using more non-ionic emulsifier and then test it again using freeze/thaw cycles.

 

Emulsion stability problem 4: your cream or lotion changes viscosity in different climates

A properly formulated cream or lotion should not show significant changes in viscosity in different climates. If it does, it is usually caused by:

• using too high an input of low melting point butters OR
• using non-ionic emulsifiers only without sufficient gums or polymers.

Both non-ionic emulsifiers (when used on their own, with out gums or polymers) and low melting point butters will be subject to climate induced viscosity changes, and can be easy to fix but you need to revisit your emulsion formula and start again.

Make sure you limit the input of all low melting point butters to 10%w/w at most. When using non-ionic emulsifiers to form your emulsion, make sure you also incorporate sufficient gums or polymers to help hold the form of the emulsion in warmer climates.

What other causes are there of emulsion instability?

Another common cause of emulsion instability is the method used to create the emulsion. Sometimes more mixing is not better! Here are some scenarios:

• high shear mixing with shear sensitive polymers will irreversibly cut the polymers and render them useless as stability aids. Check the gums or polymers you are using can handle high shear before mixing your emulsion formula.
• incorporating too much air into your batch while mixing, through incorrectly positioned stirrers, can cause viscosity changes and oxidation in the finished product. Make sure the rate of shear, vessels and mixing equipment suit the batch size as well as materials used.
• not mixing sufficiently will lead to large droplet size in the emulsion, and the larger the droplet size, the faster oil droplets will coagulate and coalesce, and the faster the rate of stability. You should use high shear to create your emulsions where ever non-shear sensitive materials are in your formula to ensure the smallest droplet size possible in an emulsion.

Investigate other cosmetic formulation mistakes with this video.

It is a company responsibility to ensure that all cosmetic products they put onto the market have adequate stability data to support the shelf life and time of sale of the product. Find out more in this video: Who’s responsible for faulty product? This helps protect the safety and quality of the product, so that it is safe, stable and efficacious for a consumer to use.

Make sure your cosmetic brand conducts the necessary stability checks on all products it releases into the market, whether they manufacture them or not, because you are ultimately responsible for those products!

Most importantly, when formulating emulsions, make sure you know how to trouble shoot what has gone wrong with your emulsion formula to make better samples each time.
 

Happy formulating!