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Alcohol-free toner with 2% Salicylic acid
I am formulating a toner that contains 2% salicylic. Target pH of the toner is 4.5 to 5.5 (pKa of SA is 2.97 so I adjusted target pH to be higher than this). I mixed it under gentle heating with 2% glycerin, 8% 1,3-propanediol and 0.8% PEG-40 hydrogenated castor oil to fully solubilize the acid.
I added this premix into water with EDTA and 0.8% NaOH. I added other actives and extracts.
Im worried if this doesn’t work.
My colleague made the formula. She was able to dissolve the SA by heating it in water, thorough mixing and added with NaOH. Her output was a clear solution. Our client approved her formula. Then 3 months passed, I checked her retention sample. Then I noticed suspending precipitates in it. So I modified her method as I’ve detailed above.
I wanna know if my method was right just so no precipitation would happen. If it’s not, is there other way to do this right?
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12 Replies
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Salicylic acid is most effective between ph 3 and 4. The free acid can penetrate skin better for best results.
By adding sodium hydroxide you’re creating sodium salicylate which won’t be able to penetrate, but is definitely more water soluble.
if you care about performance you may want to avoid NaOH altogether and just use a higher percentage of polyols in the formula. You want the free acid available as much as possible for maximum effect.
But let’s see what others say here.
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letsalcido said:Salicylic acid is most effective between ph 3 and 4. The free acid can penetrate skin better for best results.
By adding sodium hydroxide you’re creating sodium salicylate which won’t be able to penetrate, but is definitely more water soluble.
if you care about performance you may want to avoid NaOH altogether and just use a higher percentage of polyols in the formula. You want the free acid available as much as possible for maximum effect.
But let’s see what others say here.
I agree with you on this. I am also worried on the exfoliancy. The toner claims to be an anti-pimple product. Having sodium salicylate in it makes it an anti-aging product. This is something I need to discuss with our sales team.
I did try cooling down the SA premix but it just crystallizes. This is when I thought I need to adjust the pH of water first, make it alkaline, before adding the SA premix so that it won’t crystallize.
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It needs a lot of glycols and a surfactant to stop recrystalization. There are studies showing it’s still effective at pH 6. You will have better chance to stabilise it at 6. Or you would have to use unpleasant amount of propylene glycol.
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@ngarayeva001 that changes everything! Do you have links to those studies?
I’ve been trying to formulate a shampoo for myself with salicylic acid, and if proven effective in salicylate form it would make this so much easier.
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You will need on the order of 25% to 30% Propanediol. Add 1% Sodium Citrate and that will help solubilize the SA. As mentioned above, ditch the NaOH. Keep your pH between 3.0 and 4.0. Add 2% Polysorbate 80.
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You will need on the order of 25% to 30% Propanediol.
I can see this is not going to be an inexpensive product. -
MarkBroussard said:@JamesLD:
You will need on the order of 25% to 30% Propanediol. Add 1% Sodium Citrate and that will help solubilize the SA. As mentioned above, ditch the NaOH. Keep your pH between 3.0 and 4.0. Add 2% Polysorbate 80.
I cant add more Zemea since it’s quite pricey. Does adding 5% Propylene Glycol will make it work?
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@JamesLD You probably want around 30% polyol content. So probably you would need to add 20% PG at least to your current formulation. If you opt to go with it, you could also just get rid of its isomer 1,3-propanediol and just try out 30% PG.
I was in fact formulating a salicylic acid toner as well, and 20% PG did not work on its own, but didn’t try > 25% as suggested. Didn’t spend any more time on it and used alcohol.
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Just realized I actually meant glycols not polyols (is one not a subset of the other?).
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BASF has a product that is Salicylic Acid complexed with Acacia Gum that is a spray-dried solid and goes right into solution in water, no other solvent required. You might cost compare that ingredient versus Salicylic Acid + Propanediol + Propylene Glycol. It’s very easy to formulate with.
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Thank you everyone for your inputs. I will have a meeting with our Sales and recommend to have the toner reformulated for a number of reasons.
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alternatively, you can create an emulsion with a very polar oil phase and solubilise the salicylic acid that way
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