The answer to this question is a gigantic quagmire of “it depends”.
Generally speaking, it’s experimentation, taking notes, learning, and trying over and over again. Think of it a bit like cooking without a recipe—how do you know how much onion to use? How do you know which flavours will work together? Experience, experimentation, and time 🙂
For individual formulations I’ve shared, please start by reading the entire blog post. If there’s a very particular reason I’ve used something at a specific rate, it will likely be discussed/explained in the post.
You’ll also want to look at the maximum and recommended usage rates for the individual ingredients. Give this post a read to learn more about that. For ingredients like emulsifiers and preservatives, the “why” for the amount is usually “that’s the amount required to get the job done.” Though the “the” can still be a bit subjective—it might be better to say “that’s an amount that gets the job done.” Imagine you’re seasoning a sauce to taste; there’s a lot of space in the “not enough salt” and “too much salt” realm, but there’s also some space in the “that works, mmm tasty” realm as well. It could be that 0.5% preservative is enough if the formulation is in a squeeze bottle, but not if the formulation is in a tub. It depends.
Then there’s the entire context of the formulation—both what it is and what else is in there. For example, one lotion might have more or less of a thickener than another, and there could be dozens of reasons for that: desired skin feel, the emulsifier used, desired end consistency, compensating/countering other ingredients used in the formulation, etc. For some cooking/baking metaphors:
- You’d use more sugar in a cake than in a loaf of bread. Why? Because cake is sweeter than bread, and sugar is what makes it sweet.
- But, you’d use less sugar in a cake recipe that included other sweet ingredients, like bananas, vs. a recipe that didn’t.
- You’d use more water/broth in a soup than in a sandwich. Why? Because soup is wetter/more liquid than a sandwich, and water/broth is the thing that makes food more liquid.
- But, you’d use more broth in a soup recipe that contained a lot of dry ingredients, like pasta and lentils, than one that contained a lot of fresh ingredients, like tomatoes and squash.
And of course, there’s also personal preference. A formulator with sensitive skin or specific allergies will make different decisions than a formulator who doesn’t. If you live somewhere very hot you’ll need to create products with higher melting points than someone who lives somewhere significantly cooler.
Posted in: Measurements
