Lotions: Emulsification – what’s that then? (updated)

A few times I’ve mentioned using polysorbate 20 or 80 to mix your oils into water. But what are these ingredients? They are emulsifiers. (If it’s in bold, you know it’s important!) Normally, oil and water don’t like to mix. Water is polar, oil is non-polar, so the oil just floats on top of the…