oil based and emulsified scrubs and why he would choose one over the other.
The functions of the two scrubs are quite similar - they are both intended to exfoliate the skin with salt, sugar, or other scratchy things and leave behind a nice oily film - with one key difference - the emulsified scrub turns into a lotion type product when water is applied while the oil based scrub is rinsed off when water is applied and doesn't turn into a lotion type product.
In an oil based scrub, we use only oil soluble ingredients like oils, butters, and esters. In an emulsified scrub, we use oil soluble ingredients like oils and butters, but we can include water soluble ingredients because we're including an emulsifier - Polawax, e-wax, BTMS-50, or another emulsifier of your choice - so you could add some humectants or proteins or other water soluble ingredients.
With an oil based scrub, you will likely need to mix the product before using it as the salt or sugar will sink to the bottom of the container, whereas the exfoliant is suspended in the emulsified scrub. (I say you will generally need to mix the product - with the manicure scrub I've linked to below, if you put a ton of salt or sugar into it, you won't need to mix it as it is very thick!)
water activity, and it was very interesting!) If there's a chance water might be introduced into the product - through wet hands, being in the shower, and so on - I believe you need to add an oil soluble preservative, which will generally be a paraben based preservative, like Phenonip or Liquipar Oil. I'd suggest putting an anti-oxidant into either product to make the oils and butters last longer,
As an aside, my mother is very good at never putting her wet hands into a scrub, always using a one-time use plastic spatula or spoon, but most people will put their wet hands into the product regardless of their good intentions! And good intentions won't preserve a product, no matter how many people put it on their cutesy labels along with "love" and "blessings". (I always think of Ned Flanders going off on the townspeople of Springfield after they re-build his house when I hear the phase "good intentions". It makes me laugh.)
Here's one of my favourite manicure scrubs with lecithin and lanolin. It can feel very greasy at first, but after a few minutes, that feeling will dissipate and you'll just feel moisturization. When I make this recipe at home, I admit I don't use a preservative because the product is primarily for my mom (and secondarily for me) and we are both really good at not putting our hands into it. But when I make it for others, I always include Phenonip.
Just a few thoughts for today!