Foaming formulas with stability problems: what is the cause? 

Foaming formula stability problem 1: colour and aroma changes in your foaming formula

When you have colour or aroma changes in your foaming formula, you’ll first need to decide if the changes are significant enough to impact a consumer, as well as the safety and performance of the finished product. Small differences in colour or aroma may be tolerated by consumers, but large differences in pH or viscosity will adversely affect the flow and probably the foam of the product and render it unfit for sale.

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

• add a small input of chelating agent and see if this restores the original colour. Find out about chelating agents here.
• remove or reduce plant or essential oils that are susceptible to oxidation; or add a little vitamin E to prevent oxidation. Careful – any oils or vitamin E added can reduce foam and cleansing performance, so amend inputs with caution! Watch this video to see how to test if you are using the right input of vitamin E.
• you may also need to check microbial counts to ensure there is no contamination of your foaming formula.

Foaming formula stability problem 2: powdery or lipid layer forms on top

If you see a powdery or lipid layer forming on top of your foaming formula, the causes are either:

• insufficient surfactant or solubilizing agent for the lipid content OR
• insufficient mixing of the surfactant/solubilizing agent before it is added to the water phase

It will take another sample to fix this. In the next sample, try:

• checking the ratio of surfactant or solubilizing agent to oil content first – this includes all oils present, such as plant oils, essential oils, fragrances and antioxidants.
• make sure this ratio is significantly in favour of the surfactant or solubilizing agent, then remember to mix the oils into the solubiliser or surfactant thoroughly, without introducing air, before adding to the water phase.

It could also be that you are trying to solubilise too much oil phase in a surfactant with a high water content. If that is the case, you may need a straight solubilizing material to provide effective solubilizing power and mix that with your oils first, before adding to the surfactant phase, to resolve this issue.

 

Foaming formula stability issue 3: a gummy or gel layer forms

When formulating more natural surfactant formulas, it can be difficult to build the required viscosity into your foaming formula without the use of gums. Even when using more conventional surfactants, you may want to add certain gums for conditioning properties. In either case, when not added using the correct method, these gums can form jelly like layers in a foaming formula – either at the top of the product or at the base.

To fix this issue:

• make sure you mix all surfactants and water phase together BEFORE adding the gum to the formula. This ensures that when you add the gum to the formula, it will hydrate with all available water.
• make sure you check the correct method for adding the gum or polymer – for some gums you will need to take the pH up to ensure it gels properly and then reduce it to suit the skin and hair; for other gums or polymers you may need to acidify before bringing the pH back up. Make sure you understand proper gum selection and which environment or method steps suit the gum you have chosen with further study, or at a beginner level with our How to choose cosmetic gums workshop.
• always follow the supplier instructions when it comes to neutralization of more innovative polymers.

Foaming formula stability issue 4: drop in viscosity

The use of some actives and especially some essential oils can cause an irreversible decrease in the viscosity of a foaming formula. In some cases, using certain actives or essential oils just isn’t possible with some combinations of foaming ingredients.

Other causes of a drop in viscosity could include:

• a significant change in pH – this is one of the most common causes of viscosity change, so if you notice a big drop in viscosity, check the pH. If pH is the cause, you will need to isolate what caused the pH change and fix that to also correct the viscosity issue.
• if you have used salt to thicken the product, it too can be impacted by a change in pH.
• when using salt to thicken your formula, be very careful with the input: remember, too much salt can irreversibly thin the product and this can change from batch to batch.
• oxidation can cause a change in pH which can then impact viscosity. Consider this when conducting your instability investigations; if there is a colour or aromatic change as well as a pH change, it could be oxidation.
   

What other causes are there of foaming formula instability?

Other causes of foaming formula instability could include:

• the use of vanilla essential oil can turn your formula brown to black over time, even when sufficient antioxidant is used.
• some preservatives can turn formulas pink or brown when a citrus fragrance or essential oil is present.
• foaming formulas can change colour when they become excessively alkaline or acidic, and their viscosity can thin dramatically too – so ensuring good pH stability is essential to prevent colour and viscosity changes.

Remember too that ‘scum’ can form around the base of showers or the rim of bathtubs if chelating agent is not used with certain surfactants such as most sulphates.

If you are formulating foaming exfoliant products you will need to make sure you have incorporated suitable gums to stabilize these particles otherwise they are particularly susceptible to floating toward the top or sinking to the bottom.

Finally, be careful with your mixing! Using high shear does not suit foaming formulas because they are meant to foam. Even low shear mixing can cause the introduction of a lot of air that can then take a long time to settle out, or cause gel layers or viscosity changes. Make sure you keep your low shear mixers below the surface of product and sufficiently low to avoid sucking air into the formula during the mixing phase; and that vats suit the batch size of product to be made.

Investigate other cosmetic formulation mistakes with this video.

You need to ensure your foaming formulas are stable over the shelf life of their sale and then when in use by consumers. Find out more in this video: Who’s responsible for faulty product?

Make sure you know how to conduct the necessary stability checks on your foaming formulas, and more importantly, how to trouble shoot and fix your foaming formulas when things go wrong.

Happy formulating!