salicylic acid in your products, something I'll be discussing as we get back to making toners in the Newbie Tuesday series on facial products, which starts again on Monday, January 16th.
What you see here is willow bark, not salicylic acid, but I don't have any of the latter at home and I really wanted a picture to go with this post!
Formulating for acne for pharmacists - This is a really interesting document if you're interested in learning more about using salicylic acid and other powerful ingredients for acne. I will warn you that the formulae aren't by weight, but I trust that pharmacists won't steer us wrong, and they're using ingredients at much higher levels than we do at home. But it's an interesting read for learning more about how to formulate for acne prone skin.
As an aside, I had terrible acne as a teenager, and the only thing that worked for me was a prescribed sulphur product that I had to mix together myself. I think that's on this sheet!
Solublity of salicylic acid in organic solvents - This is a great article if you want to learn about all the possiblities for dissolving salicylic acid. For instance, it dissolves at 1.592 M in propylene glycol or 2.087 M in ethanol.
Salicylic acid has a molecular weight of 138.122 g/mol, meaning that 219 grams of salicylic acid will dissolve in 1 litre of propylene glycol or 21.9 grams will dissolve in 100 grams of propylene glycol. So if you wanted to add 2% salicylic acid to your product or 2 grams of salicylic acid to 100 grams of product, you'd need to dissolve that 2 grams in around 10 grams of propylene glycol. (To be accurate, 2.19 grams will dissolve in 10 grams of propylene glycol.)
Using salicylic acid in our formulations - This is a great document from ULProspector about using SA, and I feel it offers a good picture of how much work it is to incorporate it into a product. (I prefer white willow bark as it is so much easier to use!)
Mixed-solvency approach (PDF) - This all about the different ways salicylic acid could be dissolved, and what combinations might be better than just one solvent alone. It really is a fascinating read, and the place where this picture arises. This is something I need to experiment with in the near future as I find it so interesting that we can add
Personal Formulator FAQ on salicylic acid: Salicylic acid is only slightly soluble in water, one gram dissolves in 460mL water. To incorporate salicylic acid to a formulation, the following methods can be used: 1) it can be added to the oil phase of the emulsion and heated to 80-85C 2) it can be added to a water phase containing sodium phosphate, borax, alkali acetates or citrates to increase its solubility in water 3) it can be combined with a glycol, such as propylene glycol and alcohol If crystalization occurs over time, the concentration of salicylic acid in glycol may be too high. The typical use level of salicylic acid is 0.5-2%.
Join me Monday when we start looking at adding cosmeceuticals to our facial toners!