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# I made several substitutions to one of your formulations and it didn’t work out—why?

The more changes you make to a formulation, the harder this question is to answer.

Generally speaking, if you made one change, and your end product ended up being drastically different than mine, it was probably that one change that caused that difference. One variable means it was probably that one variable that caused that one change.

As the number of changes increases, so does that number of variables and the number of possible reasons for a different end product. Say I used ingredients A, B, and C and you used ingredients A, X, and Y (swapping B for X and C for Y)—and your end result is drastically different than mine. It could be that X + Y ingredients don’t work well together. Maybe ingredient Y conflicts with ingredient A, but so A + X + C would’ve been fine, but A + X + Y isn’t. There are a lot of possibilities, and the more changes you make, the number of possibilities increases substantially.

Sometimes I’ll be able to tell what went wrong knowing what those ingredients were, but the more variables there are, the harder it is to identify where the problem might be.

In order to troubleshoot the issue, you’ll need to re-make the formulation multiple different ways in order to isolate the variables and see where the problem crops up. So, from the example above, you’d need to make A + X + C and A + B + Y to isolate if it was X or Y causing the issue. If both of those test versions are fine, then you know it is X + Y causing the issue.

If we add a third variable ingredient, the number of experiments you’ll need to do to isolate the problem grows—a lot. Let’s look at “formulation” A + B + C + D vs. A + X + Y + Z.

The original formulation with just one of the new ingredients:

• A + B + C + Z
• A + B + Y + D
• A + X + C + D

And then the original formulation with two of the new ingredients, in different pairings

• A + B + Y + Z
• A + X + C + Z
• A + X + Y + D

You can see that adding just one new substitution (from 2 to 3) took us from 2 isolation experiments to 6. Each additional substitution is going to increase that number substantially.

Thankfully, some critical thinking and common sense can often narrow things down and give you a decent starting point:

• If you changed the thickener, and your end product has a drastically different viscosity than mine, I’d look at the thickener first
• If you changed the emulsifier, and your end product has a drastically different viscosity than mine (or the emulsion fails), I’d look at the emulsifier first
• If you changed the preservative, and your end product has a drastically different shelf life than mine, I’d look at the preservative first
• If it’s a surfactant product and you’ve used a different essential oil or fragrance oil… that can get weird. Read this blog post for an idea of how weird!