Iron chemist: Sodium lactate, Matt asks: When you say "I use sodium lactate at 2.5% or lower in my products because at 3% it can make you sun sensitive" Do you mean the total concentration of sodium lactate should not exceed 2.5%? I have the liquid version which is a 60/40 blend of sodium lactate/water so I could use up to 4.15% and still be sun safe correct?
Yes, we take into account the active amount of the ingredient when we have guidelines like this, so using 4.15% of the bottle of sodium lactate you have would give you 2.5%. I tend to use the sodium lactate at 2.5% because my hand could slip when I'm formulating, and I could easily have 3% or higher in a couple of drops. 2.5% means I'm quite below the maximum suggested usage rate but well within the guidelines of using it as a great humectant.
Which leads to another question - what's the deal with active amounts of ingredients? We see this with a lot of our liquids, especially surfactants. For instance, you mention your sodium lactate is 60/40, meaning 60% sodium lactate and 40% water. So when we use 2 grams of this sodium lactate, we are only getting 1.2 grams of actual sodium lactate, the rest being water and (probably) preservative.
SLeS - listed as "x% is the maximum usage", then that relates to the active amount of that surfactant. I use Stepan Steol CS-230, which contains 26% active SLeS and is a 2 mole version. For SLeS, we find mild to moderate skin irritation at 10% active. So if you used 40% SLeS in your body wash, you'd get 10.4% active SLeS in your product, which could cause some mild skin irritation. You wouldn't want to use that much of one surfactant in any product, so it's safe to say that this is a less irritating surfactant than SLS and on par with most of the others we'll be investigating!
When I write a recipe, I'm writing it for the ingredients I have in my house, which are the same supplies you'll find at your favourite retailer. When I use SLeS at 10% in a recipe, I'm using 10% of the ingredient as it pours out of the bottle. It might then contain 2.6% active SLeS or 8% active SLeS. I'm using the product as I see it, not as it breaks down into active ingredients. If you want to figure that out at home, then feel free to do so. You can generally get the information from your supplier about the active amount. I'm just looking at the bottle and using it that way.