what do you want to know?) I'm happy to write something like that up...but every time I try, I'm bogged down by the idea that you can substitute so many things for other things that I don't get past the fourth item!
The easiest way to know how to substitute one ingredient for another is to know your ingredients.
Picture this as my substitution suggestion: If you don't have cetyl alcohol, then use stearic acid. It's a good suggestion, but I could also suggest behenyl alcohol, cetearyl alcohol, or cetyl esters. I could just as easily suggest that you add some mango, cocoa, kokum, sal, or shea butter if your goal is to thicken the product. Each suggestion is dependent upon the type of product you're making.
Let's say I make a blanket suggestion to use mango butter in place of cetyl alcohol for thickening power...if I were to make some hair conditioner, I've just reduced the conditioning power and increased the greasiness. If we were making a body butter, I've just reduced the feeling of greasiness, but I've also reduced the thickness. If we were making a whipped shea butter, I've just removed something that will stiffen the product pretty dramatically and added another butter that will do nothing for the melting point. If we were making...well, you get the idea.
If you've ever substituted stearic acid for cetyl alcohol in a body lotion recipe, you'll know that it affects the skin feel of your product. Cetyl alcohol makes my body butter feel and look like Cool Whip, all shiny and soft, easy to spread on my skin. Stearic acid makes it look and feel like whipped butter, harder to get out of the container, harder to spread, but longer lasting on my skin. It's amazing how just a 3% switch can radically change a product.
cetrimonium chloride, for example, learn what cetrimonium chloride brings to the party. From the post on this ingredient, "it isn't as lubricating as BTMS or cetab (cetrimonium bromide), but it does have a unique ability to detangle, which means it reduces the combing forces and friction in your hair, which is a very very good thing." If we wanted to find something else that might work in place of cetac, we know that it isn't as lubricating as BTMS or cetrimonium bromide, so those won't be substitutions, and we know that it detangles and reduces combing forces and friction on our hair, so that's the quality we want to find in another ingredient.
What else can act as a detangler? We know BTMS and cetrimonium bromide detangle, but not as well as cetac. What about Incroquat CR? It's "a good detangler and a good anti-static product." This might work! Or we could just leave out the cetrimonium chloride and see what happens.
Incroquat CR would be my official substitution suggestion for cetrimonium chloride, but there really is no substitution for its detangling awesomeness. I've tried every variation I can think of to get more detangling without cetrimonium chloride, and it really is a unique ingredient that does what it says very well at up to 2% in your conditioner!
The only way to really know what you can substitute and what will feel good to your skin is to learn your ingredients and what each brings to your products. You know if you like a greasy or dry feeling lotion, so only you can decide if you want to switch the butter for cocoa or mango. They offer the same function in a body butter - they thicken and offer serious emollience - but they will feel very different.
Substitutions are dependent upon the function of the ingredient in the product and the function of the product, and it's hard to separate one from the other. The information on this blog is also dependent upon my personal preferences - for thickeners, I could suggest using something like xanthan gum or a polymer, but I generally don't - and what I have available to me at my local retailers. I can make suggestions like this one - stearic acid and cetyl alcohol can be interchanged when they behave as thickeners in a recipe - but it really is up to you to know your ingredients, your personal preferences, and your product.
I know this isn't an easy suggestion. It takes time to learn your ingredients, then learn how to use them, and time isn't something we all have a lot of these days. But if you want to make substitutions or be able to make your own recipes, you have to learn what each ingredient brings to the product and know what they feel like on your skin.
Let's take a few days to look at a few substitutions and how they might affect our products!
Related posts: All the posts with substitutions in the label!
Figuring out what's important in a conditioner