Oil Phase vs Water Phase in Emulsions
What goes where, why it matters, and how to process both phases correctly
Every lotion, cream, and emulsion-based product is built from two phases plus a cool-down stage. Understanding which ingredients belong in each phase — and why — is foundational to making stable emulsions consistently.
The three stages
| Stage | Temperature | What goes in |
|---|---|---|
| Oil Phase | 70–75°C (158–167°F) | Oils, butters, waxes, emulsifier, oil-soluble actives |
| Water Phase | 70–75°C (158–167°F) | Distilled water, hydrosols, humectants, water-soluble ingredients |
| Cool-Down Phase | Below 40°C (104°F) | Heat-sensitive actives, fragrance, essential oils, preservative (most types), pH adjuster |
Both phases are heated separately to the same temperature, then combined (water into oil, or oil into water depending on method), then cooled with continuous mixing.
Oil phase ingredients
The oil phase contains everything that is oil-soluble, plus solid ingredients that need heat to melt:
- Carrier oils — sweet almond, jojoba, sunflower, argan, and all liquid oils
- Butters — shea, mango, cocoa, kokum (all melt during heating)
- Waxes and thickeners — beeswax, candelilla, cetyl alcohol, cetearyl alcohol
- Emulsifier — Polawax, BTMS, Olivem 1000, glyceryl stearate, and others
- Oil-soluble vitamins and actives — tocopherol (vitamin E), retinyl palmitate, CoQ10
- Silicones — dimethicone, cyclomethicone (added to oil phase or cool-down)
Water phase ingredients
The water phase contains everything water-soluble plus ingredients that disperse in water:
- Water — distilled water as the base; aloe vera juice, hydrosols, or herbal infusions can replace part of the water
- Glycerin and propylene glycol — humectants, dissolve in water phase
- Hyaluronic acid — pre-dissolved in water (can take 24+ hours to hydrate fully)
- Panthenol (pro-vitamin B5) — water-soluble; goes in water phase
- Allantoin — water-soluble; needs heating to dissolve at higher percentages
- Niacinamide — water-soluble; stable at heat; goes in water phase
- Water-soluble preservatives — sodium benzoate, potassium sorbate (some formulators add these to the water phase before heating)
Aloe and hydrosols as water replacements
Cool-down phase ingredients
Heat-sensitive ingredients that would degrade or evaporate if added to a hot emulsion go in the cool-down phase:
- Vitamin C (ascorbic acid, ascorbyl glucoside) — degrades with heat; add below 40°C
- Fragrance and essential oils — volatiles evaporate from hot emulsions
- Phenoxyethanol-based preservatives (Optiphen, Optiphen Plus, Phenonip) — add at or below 40°C
- pH adjusters — lactic acid, citric acid, sodium hydroxide solution — pH is set in the cool-down phase once the emulsion has formed
- Peptides and some proteins — many are heat-labile
- Probiotics — very heat-sensitive; add at room temperature
Check your preservative's temperature requirement
Combining the phases
Once both phases reach the same temperature (within about 5°C of each other), combine them:
- The most common method: add the oil phase into the water phase slowly, with constant stirring or stick blending.
- Some emulsifiers (especially low-HLB or W/O types) work better adding water into oil — follow emulsifier-specific instructions.
- Blend continuously during addition — a stick blender in short pulses creates a more stable, fine emulsion than hand stirring alone.
- Continue mixing while cooling. Stopping mixing while hot allows droplets to coalesce.
- Add cool-down ingredients once the emulsion drops below 40°C (104°F).
Pro Tip