Why Did My Lotion Separate?
Diagnosing emulsion failure — what went wrong and how to fix it
Lotion separation — an oily layer on top and a watery layer below — means the emulsion has failed. The oil and water phases have de-emulsified, usually because the emulsifier could not hold them together. Here is how to diagnose which cause applies to your formula.
Diagnosis by timing
| When it separated | Most likely cause |
|---|---|
| During mixing (never fully formed) | Wrong emulsifier type; phases at very different temperatures; emulsifier too low |
| Within hours of making | HLB mismatch; emulsifier concentration too low; too much oil phase |
| After 1–7 days | Electrolyte destabilization; pH outside emulsifier stability range; cooling too fast |
| After weeks or months | Marginal stability formula; temperature stress (heat, cold, freeze-thaw); microbial contamination breaking emulsifier |
Common causes
| Cause | What to check | Fix |
|---|---|---|
| Wrong emulsifier for formula type | Are you using an O/W emulsifier for an O/W emulsion? | Match emulsifier to emulsion type; Polawax/BTMS for O/W |
| Too little emulsifier | Is emulsifier below 3% of total formula? | Increase to 4–8% for most formulas |
| HLB mismatch | Does emulsifier HLB match required HLB of oil phase? | Calculate required HLB; adjust emulsifier blend |
| Phase temperature mismatch | Were both phases at same temp when combined? | Heat both phases to 70–75°C (158–167°F) before combining |
| pH outside emulsifier range | Was acidic ingredient added directly to hot emulsion? | Adjust pH at cool-down; dilute acids before adding |
| Electrolyte overload | High niacinamide, sodium benzoate, salt, or brine? | Reduce electrolyte ingredients; use electrolyte-tolerant emulsifier |
| Mixing stopped while hot | Did you stop stirring before the emulsion cooled? | Mix continuously from 70°C down to at least 40°C |
| Too much oil phase (over 40% in O/W) | Check oil phase percentage | Reduce oil phase or switch to W/O formula type |
The most common culprit: not enough emulsifier
Most DIY and blog-sourced recipes under-dose emulsifier to reduce greasiness or cost. An emulsion can form and hold briefly with inadequate emulsifier, only to break within days as the emulsion slowly coalesces.
Emulsifier usage rates by system
Polawax (Emulsifying Wax NF): 3–8% — use at 25% of oil phase weight as starting point
BTMS-50: 3–8% — conditioner base; leave-on hair and skin
Olivem 1000: 3–8% — skin-compatible; pH sensitive below 5.5
Glyceryl stearate SE: 3–6% — co-emulsifier; use with polysorbate or other primary
Glyceryl stearate (non-SE) is not a complete emulsifier
Prevention
- Use a complete emulsifier system (Polawax, BTMS-50, Olivem 1000) at 4–8% of total formula.
- Heat both phases to 70–75°C (158–167°F) before combining.
- Mix continuously — use a stick blender in short pulses — while cooling from 70°C to below 40°C.
- Adjust pH only in the cool-down phase, below 45°C, using diluted acid.
- Run a stability test at room temperature and 40°C (104°F) for 4 weeks before finalizing any formula.
Pro Tip