After learning how to incorporate essential oils into water using polysorbates, many people notice something interesting. The product works, but it is often slightly cloudy, sometimes leaves a light film on the skin and occasionally feels a bit “soapy”.
This is not a mistake. It is the normal behaviour of surfactant-type solubilizers.
In more refined cosmetic formulations, however, another material is very frequently used instead: PEG-40 Hydrogenated Castor Oil.
what PEG-40 Hydrogenated Castor Oil actually isPEG-40 Hydrogenated Castor Oil is a solubilizer derived from castor oil. The oil is first hydrogenated to improve stability and then chemically modified so that the molecule becomes dispersible in water.
The result is a material that can hold aromatic oils inside an aqueous base without forming visible oil droplets.
Like polysorbates, it does not truly dissolve oil in water.
It forms microscopic dispersions that keep the aromatic material evenly distributed throughout the product.
Its role is functional, not decorative.
It allows a water-based cosmetic to contain fragrance or essential oils safely and predictably.
Although both materials are solubilizers, they do not interact with the skin or the formulation in exactly the same way.
Polysorbates are surfactants first and solubilizers second. Because of this, they can give:
- slight foaming
- a mild “cleanser” skin feel
- a faint residue in leave-on products
PEG-40 Hydrogenated Castor Oil behaves closer to a perfume solubilizer. It produces:
- clearer solutions
- less foam
- softer after-feel
- better tolerance in leave-on products
This difference is the main reason formulators often switch to it in facial mists and toners.
where it is commonly usedYou will frequently find PEG-40 Hydrogenated Castor Oil in:
- facial mists
- hydrosol toners
- aftershaves
- micellar-type waters
- scalp tonics
- perfume sprays
In these types of products clarity and skin feel matter as much as stability. A spray that looks clear and feels light is more likely to be used daily.
how to use it correctlyThe method is the same basic principle used with polysorbates.
Never add essential oil directly into water.
- Measure the essential oil or fragrance
- Add PEG-40 Hydrogenated Castor Oil
- Mix until fully uniform
- Add the blend into the water phase with stirring
Only after the oil is pre-mixed with the solubilizer can proper dispersion occur.
typical working ratiosGeneral working guideline:
1 part essential oil : 3–6 parts PEG-40 Hydrogenated Castor Oil
Examples:
Facial mist
Essential oil: 0.2–0.4%
PEG-40 HCO: 0.8–2%
Body mist
Essential oil: 0.5–1%
PEG-40 HCO: 2–4%
Heavier essential oils (patchouli, sandalwood, resins) may require higher ratios.
If oil rings appear after 24 hours, more solubilizer is needed.
important formulation notes- It is not an emulsifier for creams.
- It is not a preservative.
- It does not make a product natural because it comes from castor oil.
- A preservative system is still required in any water-based product.
A clear product is not necessarily preserved and a preserved product is not necessarily solubilized. These are separate formulation steps.
when to choose it instead of polysorbatesUse PEG-40 Hydrogenated Castor Oil when:
- you want a clear facial mist
- the product is leave-on
- you want minimal residue
- a fragrance blend does not solubilize well with Polysorbate 20
Polysorbate 20 remains perfectly adequate for many simple formulations. PEG-40 Hydrogenated Castor Oil becomes useful when you want a more refined cosmetic result.
a practical comparisonPolysorbates are reliable and beginner-friendly. PEG-40 Hydrogenated Castor Oil offers a more elegant final product. Both have a place in formulation. The choice depends on the product type and the sensory profile you want to achieve.
If you are new to incorporating essential oils into water-based products, you may want to start with my general guide on How to Safely Add Essential Oils to Water-Based Cosmetics.
For a detailed explanation of how polysorbates work and when to use Polysorbate 20 or 80, see the related article Polysorbate 20 vs Polysorbate 80: What They Are and How to Use Them in Cosmetics
