Why did my emulsion separate?

Explanation

The books do not troubleshoot a broken emulsion one symptom at a time, but between them they give the method a stable emulsion depends on, and each failure maps back to a step.

The skin care book's emulsions use an emulsifier at 3–5% plus cetearyl alcohol, both phases heated to the same 70–72 °C, the oil poured into the water in a thin stream, 3–4 minutes of high-speed mixing, then slow stirring while the cream cools and a 24-hour rest. Combining phases at different temperatures is the single most common cause of a cream that looks perfect warm and splits overnight.

The hair care book adds the general rule for order of addition — hydrate gums first, dissolve the main surfactants, add conditioners, cool below 40 °C before heat-sensitive actives and fragrance, adjust pH, then add the preservative last — and it asks for cycle testing (alternating hot and cold for 24–48 hours each) plus long-term shelf testing before a formula is called finished. Comparing your process against those steps is the reliable way to find which one failed.

What to do

• Check both phases reached the same temperature, 70–72 °C, before you combined them.
• Check the emulsifier is dosed at 3–5% of the total batch, not of the oil phase.
• Use high shear for the first 3–4 minutes, then gentle stirring as it cools.
• Run a cycle test before trusting a new formula.