this post about humectants, there have been quite a few comments I thought I would share with you, my wonderful readers! And since I'm currently planning a series on creating products for dry skin that relies heavily on the usage of humectants, this seems like a great way to start a series on those ingredients!
seventh77 asked: Hi! Do you ever use both sodium PCA and sodium lactate together in one formula, or would you advise against that?
Hi seventh77! No, I don't tend to use them together. Why? I'm not really sure. I think they would make a good combination used at something like 2% each in the water phase of a product. I think the main reason I don't use both together is that I can't find sodium PCA locally, and it costs a lot more. (Sodium lactate at Voyageur is $5.95 for 8 ounces. Sodium PCA at Personal Formulator is $5.65 for 4 ounces and I have to have it shipped to me.) In fact, there's an ingredient called Lactil you can get containing sodium lactate, sodium PCA, glycine, fructose, urea, niacinamide, inositol, sodium benzoate, and lactic acid, which clearly combines a ton of different humectants into one ingredient, so it doesn't appear there's any reason not to use them together.
Anyone have a reason why we shouldn't use these two humectants together? I'm open to suggestions!
I've never noticed sodium lactate adding a slip to a product - normally something that adds slip is either oily or alkaline in nature. Sodium lactate has a pH of about 7 (neutral, like water), and it isn't an oil, so I'm not sure why it would add any slip. It is used as a bar hardener for soap and syndet bars, but won't do anything for the thickness of your lotions.
The ability of humectants to bind water can depend upon the humidity levels. Take a look at this chart, which shows that PCA has better binding abilities at 52% and over or 31%, but sodium lactate is better at 50%. I'm not sure how much I trust this chart as it appears that glycerin isn't that great compared to just about everything else, but we know it's a good humectant.
Having said this, there are reasons to use our ingredients other than their moisture binding abilities, something we'll see tomorrow with my updated post on panthenol and the other posts I've written for this week. Sodium lactate can be a used to create a pH buffer with lactic acid and it can help with acne, something PCA doesn't offer.
Alexis asked: Hi Susan,You once posted a scale of hygroscopic abilities for humectants (sodium PCA > sodium lactate > glycerin > sorbitol). Can you also rank humectants on a scale of "tenacity"? I know glyercin is the most "sticky" and, conversely that sodium PCA and sodium lactate wash off easily. What about the others like sorbitol, panthenol, honeyquat, condition-eze, hydrovance? Is there a place on the MSDS where I would find this info? Many thanks!
I find the MSDS for an ingredient is generally pretty useless when you want information of this nature - it's better at telling you how to handle it and what to do if you eat, drink, or put it in your eyes. What you want is the data bulletin. Unfortunately, we don't tend to get much information other than "it's better than glycerin at moisture binding" for most products. This could provide enough information for you to make a decision about using humectant in general, but I can't provide more information than a theoretical glycerin > everything else.
For instance, Hydrovance claims that it absorbed 82% of its weight in water versus glycerin at 24%, but that doesn't tell us about the humidity level where this experiment might have taken place, which is something really vital for humectants. For Honeyquat, they claim that it "demonstrates a marked moisture uptake ability when compared to glycerin" in hair and "Moisture uptake studies (s)how that it has twice the moisturizing ability of glycerin". (click here for the data bulletin - notice all the typos! Seriously? No one proofread this?)
Join me tomorrow as we take another look at panthenol!