In this post, still learning asks: Wonderful site! I've been looking to understand phases in a hair conditioner and just in general. I know oils goes in the oil phase and water in the water phase. Yet, I have seen other ingredients in each phase. How do you know what goes where? Thanks.
If you're making lotions, shampoos, conditioners, or any other bath and body products, the way to know what goes where depends upon two things - the solubility of the ingredient and how sensitive it is to heat. (I generally put that information into the posts on the ingredient! If I haven't, I really should!)
The heated phase of any product should be heated and held for 20 minutes at 70˚C. The cool down phase starts at between 45˚C to 50˚C. So if something can handle 70˚C or over or quite clearly needs to be melted - like SCI, our emulsifiers, beeswax - then we know we have to put them in the heated phase of something. The oil phase should contain all the things that are oil soluble - oils, butters, waxes, emulsifiers, thickeners, and so on. The water phase should contain all the things that are water soluble - water, hydrosols, proteins, and so on. Both phases should only contain those things that can handle 70˚C or higher.
Here's an example with conditioner. If we want to add BTMS-50, we know it must be melted and it is oil soluble, so it goes in the heated oil phase. If we want to add aloe vera, we know it's water soluble and can be heated, so it goes into the heated water phase.
But let's say you want to add honeyquat to the mix. I know it's water soluble, but it's heat sensitive, so I will put this in the cool down phase. What about polyquat 7? There aren't any disclaimers about heat with this ingredient, and I know it's water soluble, so I can add it to the heated water phase or cool down phase. If I want to add dimethicone or cyclomethicone, I know both are oil soluble but I'll add them to the cool down phase because they're heat sensitive.
What happens if you include something in the heated phase that should be in the cool down phase? A lot of things! You might inactivate the ingredient, it could give off a horrible smell (like honeyquat, for instance), it could destroy the emulsion, or you could change the skin feel of the product. The most likely outcome is that you will inactivate the ingredient - this is most common with preservatives and extracts - or, as you would find with a fragrance, it'll be gone by the time you combine the two phases.
What happens if you including something in the cool down phase that should be in the heated phase? This one's a lot tougher to answer because it could have no impact at all, it could ruin an emulsion, or it could have weird side effects you didn't expect. For instance, in this intense conditioner with all my conditioning agents, if you add the cetrimonium chloride to the heated phase (I generally put it in with the water), you get a stable emulsion. If you add it in the cool down phase, you might see some separation. If I add a ton of cold aloe vera to a lotion, it might mess with the emulsion. On the other hand, I have added polyquat 7 to the heated and cool down phases of my products with no effect.
What do you do with something that might have a temperature of 60˚C or falls between the heated and cool down phase? For the most part, throw that into the cool down phase, or watch that thermometer for the right moment (I generally put those in the cool down phase to make life easier).
So what you want to know about every ingredient is the solubility - oil or water soluble - and what temperature it can take! That will determine which of the three phases you would include your ingredient!
Hope this answers your question (and I love your name - we're all still learning no matter how much we think we know)!