Ingredient lists are supposed to be written in descending order with the ingredient in the largest percentage first and the smallest percentages last. But in some cases, they're allowed to list everything under 1% in whatever order they like (I consider this the "miscellaneous" category). I know preservatives are generally used at lower than 1%, so I generally figure that's where the 1% list starts. I know other ingredients, like fragrance, gelling ingredients, fancy additives, or botanical extracts are used at 1%, so that's another indication of where I can start the 1% list.
Sometimes they fool me, though. Although I wouldn't use aloe vera at 1%, if it's only there for label appeal it could end up in the miscellaneous category. If you see it in the lower half of the ingredient list, near the preservative, then you know there's not enough to be beneficial.
If we look at this ingredient list (from Spectro Jel's cleanser, which we'll take a look at duplicating tomorrow)...
Aqua, Butylene Glycol, Glycerin, Hydroxypropyl Methocellulose, Polysorbate 20, Cetyl Alcohol (moisturizer), Hydrated Silica, PEG-12 Dimethicone, Diazolidinyl Urea, Carbomer, Triethanolamine, Sorbitan Oleate.I know that we won't be using more than 1% of the diazolidinyl urea because that's the preservative, which means the carbomer and following ingredients will be 1% or less. I'm not sure about the PEG-12 dimethicone, so I will assume (for now) that's at more than 1%.
If I'm not sure about usage rates or purposes of certain ingredients - like the hydrated silica - I visit the Cosmeticsinfo.org site and look it up for information or search through my text books. I see from the Safe as Used PDF this ingredient can be used at up to 34% safely. But it's also used as an abrasive, and I don't remember this product being abrasive, so I'm assuming it's there as a gelling agent. I know that we wouldn't use tons of gelling agent, so I'm thinking it's around the 1% mark as well. If that's the case, then the PEG-12 dimethicone would be 1% or less in this product.
There's one thing stumping me in this recipe - the hydroxypropyl methylcellulose. I know it's a gelling agent and it can be used up to 3%. So if we assume the highest we'd go is 3%, this means everything below it is 3% or less. Which means I can use a starting point of less than 3% for the polysorbate 20 (which makes sense because it's a co-emulsifier with the sorbitan oleate), cetyl alcohol, hydrated silica, and PEG-12 dimethicone. This will also relate to the amount of carbomer I use. If I'm using another gelling agent - or two if the hydrated silica is also for gelling - I know I need to use less carbomer, thus less TEA.
So if I break it down I know that I have the following amounts...
- water - whatever's left over
- butylene glycol - not sure yet
- glycerin - not sure yet
- hydroxypropyl methylcellulose - less than 3%
- polysorbate 20 - less than 3%
- cetyl alcohol - less than 3%, probably more than 1%
- hydrated silica - less than 3%, could be less than 1%
- PEG-12 dimethicone - less than 3%, could be less than 1%
- Diazolidinyl Urea - 1% or lower
- Carbomer - 1% or lower
- Triethanolamine - 1% or lower
- Sorbitan Oleate - 1% or lower
I hope I've given you some idea how to use your knowledge of your ingredients, usage rates, and skin feel to figure out how to duplicate your favourite recipes!