Solubiliser vs Emulsifier: Which one do you need in your formulations?

A solubiliser and oil in water (O/W) emulsifier both do the same job, as they both help disperse oils in water. Oil and water do not blend naturally and if you want to bring them together, you need something to keep them together.  Although they both belong to the group of surfactant (surface active) molecules, solubilisers and O/W emulsifiers are different in every other aspect and cannot be used interchangeably.

Surface active molecules, or surfactants, are a broad spectrum of molecules with broad applications, ranging from their use in shampoo to nasty materials used in drilling. These molecules have at least one water-loving (hydrophilic) and one fat- (or lipid-) loving (lipophilic) component on the very same molecule.

This means that they straddle the divide between oil and water, orienting their hydrophilic  and  lipophilic  components  accordingly. It helps to think of these molecules as tadpoles, attaching their tails and heads to either the water- or fat-loving ingredients.

Solubilisers: why do we need them?

Solubilisers are a group of surfactants that are completely water soluble but have a little bit of oil solubility. They are, as their name reveals used to solubilise an oil in water or another hydrophilic medium (such as a herbal infusion or a hydrosol). The solubilised molecule has such a tiny particle size that the solution appears either completely transparent or lightly translucent. Read our previous blog post on how to use a natural solubiliser.

Solubilisers are used to dissolve / disperse the following lipophilic (oil-loving) ingredients in water:

1. A lipophilic preservative

In this image you can see three test tubes containing the preservative Versatil TBG (INCI: Triethyl Citrate, Glyceryl Caprylate, Benzoic Acid) which is insoluble in water and needs a solubiliser for water based products such as tonics and gels. Versatil TBG has been solubilised in water in different ratios (more on this below).

2. Essential oil or a fragrance oil

In this image you can see three test tubes containing the mandarin essential oil which, like all essential oils, is lipophilic and would normally float on top of water. Essential oils need a solubiliser for water based products such as tonics and gels. In the photo you can see that mandarin essential oil has been solubilised in water in different ratios (more on this below).

Essential oils and water do not mix without a solubiliser. If you happen to receive an essential oil which easily disperses in water or glycerine, it is likely to have been diluted already with some sort of solubiliser or solvent.

3. A lipophilic vitamin such as Vitamin E

In this image you can see two test tubes containing Vitamin E (INCI: Tocopherol) which is lipophilic and needs a solubiliser for water based products such as tonics and gels. Vitamin E has been solubilised in water in different ratios (more on this below).

4. CO2 extracts 

In this image you can see two beakers containing Rosemary CO2 extract which, like all CO2 extracts, is insoluble in water and needs a solubiliser for water based products such as tonics and gels. Rosemary CO2 extract has been solubilised in water in different ratios (more on this below).

You cannot dissolve all CO2 extracts in water by applying a solubiliser.  CO2 extracts high in essential oils and light/volatile organic molecules can be solubilised, whereas CO2 extracts with a triglyceride content would not be solubilised. So as with everything to do with organic cosmetic formulation, you need to make sure that you understand the chemical make-up of your CO2 extract before you try to solubilise it.

In the photo below, we’ve dispersed Rosemary CO2 extract by applying a 1:5 and 1:10 ratio of extract to solubiliser. As you can see, the 1:5 ratio fails. The 1:10 ratio is not quite satisfactory either but at least the extract doesn’t separate.

Please note that solubilisers can only disperse light and small molecules such as essential oils. You can’t use a solubiliser to solubilise triglycerides (plant oils) in water.

What happens if you don’t use a solubiliser?

We’ve worked with many natural formulators and brands who prefer not to use any solubilisers in their quest to avoid any unnecessary ingredient in their formulations. They advise the consumer to shake the bottle vigorously before application to ensure (as much as possible) that the oil-loving ingredient is dispersed evenly throughout the product.

However, the absence of a solubiliser results in a layer of oil swimming on top of the water and any hydrophilic ingredients in the formula. But the lack of a solubiliser not only affects the appearance and aesthetic of a product; it may also result in functional and safety issues too, as we’ll explain below.

When your customer opens the bottle that contains your solubilised formulation, the essential oil and preservative is present in the same uniform concentration from the very first to the very last drop of the product.

However, if you omit the solubiliser, it’s highly likely that the essential oil will not be uniformly distributed in the bottle even if your customer follows your instructions to shake the bottle vigorously before each application. Over the years, we have had several reports about sensitivity and allergic reactions from our students who applied an essential oil or a preservative in a water-based product without using a solubiliser.

As you can see, both the intended benefits as well as the undesired hazards* of using the essential oil are possible simply because the oil is not uniformly distributed and its dosage can vary from application to application.

In case of an overdose, you’re increasing the risks of an allergenic reaction or sensitisation and in case of an under-dose your customer will not be benefiting from the functional properties of the ingredients you’ve chosen for your product.

*Don’t be alarmed by reading the word “hazards”. Most essential oils have allergenic components (benzyl alcohol, linalool, limonene, etc) and hence have maximum dermal limits for their usage in skin and hair care formulations.  Adhering to these dermal limits during formulation is not only a safe practice, it is mandatory in many parts of the world. Applying a solubiliser to keep the concentration of the essential oil uniform in the whole solution helps guarantee that the ingredients in your products will be used safely within the dermal limits at each application.

What are Emulsifiers?

In contrast to solubilisers, emulsifiers are not water soluble.  Emulsifiers are used to emulsify oils in water to create O/W emulsions. Emulsifiers are used for oils and lipophilic ingredients with bigger/heavier molecules than essential oils. These oils, for example, include plant oils, fatty esters and waxes.

Whereas with solubilisers you can incorporate only low concentrations of a lipophilic ingredient, (0.1 – 2.0%), with emulsifiers you can incorporate up to 50% oil in water. That said, most emulsifiers have an optimum oil phase concentration of between 15-30%.

In this photo, we’ve dispersed 5% of :

1. Symbiosolv clear (a natural solubiliser)
2. Symbiosolv XC (a natural solubiliser, which has now unfortunately been discontinued)
3. Easymuls plus (a liquid natural emulsifier)

You can see clearly that whereas the solubilisers are completely soluble in water, the emulsifier is not soluble. It first disperses to a milky solution but separates to two phases within a few hours as you can see in this photo from our stability test.

Although both groups of solubilisers and emulsifiers are considered surfactants and basically do the same thing, they are different in their functions and the formulations they create. You cannot replace a solubiliser with an emulsifier, nor vice versa. 

Comparison of Solubilisers & Emulsifiers: Properties & Usage

We’ve compiled a short table for you to compare solubilisers and emulsifiers side by side.

Where can you buy natural solubilisers?

Good quality naturally derived solubilisers are very hard to find. Formula Botanica works with a number of different ingredients suppliers around the world and very few of them stock the natural solubiliser we typically recommend to our students, which is called symbio^®solv. The company that manufactures this solubiliser is called Dr Straetmans. They have created three versions of symbio^®solv:

• symbio^®solv XC (INCI: Caprylyl/Capryl Wheat Bran/Straw Glycosides; Aqua; Fusel Wheat Bran/Straw Glycosides; Polyglyceryl-5 Oleate; Sodium Cocoyl Glutamate; Glyceryl Caprylate) – sadly to be discontinued in 2018
• symbio^®solv clear (INCI: Caprylyl/Capryl Glucoside; Aqua; Polyglyceryl-5 Oleate; Sodium Cocoyl Glutamate; Glyceryl Caprylate; Citric acid) – sadly to be discontinued in 2018
• symbio^®solv Clear Plus (INCI: Caprylyl/Capryl Glucoside; Aqua; Sodium Cocoyl Glutamate; Glyceryl Caprylate; Citric Acid; Polyglyceryl-6 Oleate; Sodium Surfactin) – this is Dr Straetmans’ replacement for symbio^®solv Clear and symbio^®solv XC.

Our preferred suppliers include:

SkinChakra in Germany: buy symbio^®solv clear plus

Formulator Sample Shop in the USA: buy symbio^®solv clear

New Directions Australia: buy symbio^®solv clear

Which are your favourite solubilisers? Leave us a comment below and share your favourite ingredients!

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Elham Eghbali

Dr. Elham Eghbali was Formula Botanica’s Cosmetic Chemist between 2014 and 2018. She has over 20 years’ industry experience and is based in Bavaria, Germany. To read more about Formula Botanica’s team, visit our staff page.