Why Cosmetic Formulas Separate (And How to Prevent It)

One of the most common frustrations in cosmetic formulation is separation.

A cream may initially appear smooth and stable - only to split, thin out, develop oil pockets, or become uneven days or weeks later.

Understanding why formulations separate is one of the most important steps in becoming a more confident formulator. Stability is not determined by a single ingredient alone. It comes from building balanced systems that work together correctly.

In this guide, we’ll explore the most common causes of cosmetic instability and how beginner formulators can build more stable emulsions.

What does “separation” mean?

Separation occurs when ingredients that were temporarily combined begin pulling apart again over time.

This is especially common in emulsions - formulations that combine oil and water.

Signs of instability may include:

• Oil pooling on the surface
• Watery layers forming
• Texture thinning over time
• Graininess or uneven viscosity
• Creams collapsing after temperature changes

Why emulsions are difficult

Oil and water naturally resist combining. Cosmetic formulators use emulsifiers, thickeners, and stabilising systems to keep them uniformly dispersed.

Common reasons cosmetic formulas separate

1. Incorrect emulsifier usage

One of the biggest causes of instability is using insufficient or poorly matched emulsifiers.

Emulsifiers help suspend oil droplets evenly throughout water phases. Without proper emulsification, oils eventually begin separating from the formula.

Common beginner issues include:

• Too little emulsifier
• Incorrect emulsifier selection
• Using solubilisers as true emulsifiers
• Poor oil-to-emulsifier balance

Learn more in Understanding Emulsifiers & Solubilisers in Cosmetic Formulation.

2. Insufficient viscosity support

Even properly emulsified systems often require viscosity builders to improve long-term stability.

Thickeners and gums help slow movement within the formula, reducing droplet migration and separation over time.

Common stabilising ingredients include:

• Xanthan Gum Powder
• Sclerotium Gum
• Carbomer 940
• Cetearyl Alcohol
• Cetyl Alcohol

Why stabilisers matter

Stabilisers improve viscosity, support suspension, reduce phase movement, and improve sensory feel in emulsions.

3. Poor mixing or homogenisation

Processing technique matters significantly in emulsion stability.

Even excellent formulas can fail if the oil phase is not dispersed properly during emulsification.

Common processing issues include:

• Insufficient shear
• Incorrect phase temperatures
• Adding phases too quickly
• Poor cooling-stage mixing

Many beginner formulations improve dramatically simply through better mixing technique.

4. Incorrect pH

Some thickening and emulsifying systems are highly pH dependent.

Carbomer systems, for example, require neutralisation to build viscosity correctly.

If the pH falls outside the system’s optimal range, the formulation may thin out or destabilise.

Learn more in Understanding pH in Cosmetic Formulation.

5. Unbalanced oil phases

Heavy oil loads can destabilise beginner emulsions if the system is not properly balanced.

Increasing oils without adjusting emulsifier systems or stabilisers often leads to separation.

This is why formulation systems should always be viewed holistically rather than ingredient-by-ingredient.

How formulators improve stability

Professional formulators typically improve stability by:

• Using balanced emulsifier systems
• Supporting emulsions with gums or fatty alcohols
• Controlling pH carefully
• Improving mixing and processing
• Testing formulas under different temperatures

Common beginner mistakes

Final thoughts

Want to explore more formulation ingredients?

Browse the Ingredient Dictionary.