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Acid suggestions to lower a skin cream pH while avoiding the sun-sensitizing citric acid?
I need to sharply lower a skin cream pH (to make it more acidic)
but I want to avoid using citric acid as it can make skin more sunburn sensitive
https://www.fda.gov/cosmetics/cosmetic-ingredients/alpha-hydroxy-acidsAny non alpha hidroxy acid suggestions?
I’m leaning heavily towards acetic acid. -
33 Replies
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Phosphoric acid
Hydrochloric acid -
Perry said:Phosphoric acid
Hydrochloric acidIs using HCl in cosmetics safe ?
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@Aziz - well, when diluted out in a formula it’s perfectly safe. It’s like using NaCl as it dissociates in Cl- and H+ ions. The less safe part is during production. But if you are making a batch in a lab you can make a 1% HCl solution and that is fine to use.
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Perry said:@Aziz - well, when diluted out in a formula it’s perfectly safe. It’s like using NaCl as it dissociates in Cl- and H+ ions. The less safe part is during production. But if you are making a batch in a lab you can make a 1% HCl solution and that is fine to use.
Thanks .
Can we use it like AHA or BHA in skin care products or we can use it to adjusting pH like NaOH ? -
Phytic Acid
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@Aziz - HCl does not work like an AHA or BHA. It is simply used to adjust the pH of the system in the same way that NaOH is used. It’s not meant to do anything else in the formula.
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I was going to say phytic acid as well, are the AHAs really able to cause sensitization if they are used for pH adjusting at low concentrations? I think I’ll try to look for a study on this
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Regarding phytic acid: be careful because many suppliers selling phytic acid actually sell sodium phytate or calcium/magnesium phytate which won’t do the trick.I’d say that, unless your product is really acidic and/or requires higher percentages, using any organic acid such as citric, acetic, malic, lactic or whatever to lower pH to +/- neutral won’t cause sensitisation. But that’s just a guess! -
My point is
Wouldn’t strong mineral acids like Hydrochloric, phosphoric or sulfuric acids look too harsh on an ingredient label?
Even if they’re used in tiny amounts, some customers who know no better would get scared just by reading that.Therefore I’m considering acetic acid which is found in vinegar, which some people apply vinegar on their skin.
Concentrated acetic acid smells nasty, but we’ll see if the finished product does when diluted. -
What are you using in your cream that it needs that much pH adjustment?
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Gunther said:My point is
Wouldn’t strong mineral acids like Hydrochloric, phosphoric or sulfuric acids look too harsh on an ingredient label?
Even if they’re used in tiny amounts, some customers who know no better would get scared just by reading that.Therefore I’m considering acetic acid which is found in vinegar, which some people apply vinegar on their skin.
Concentrated acetic acid smells nasty, but we’ll see if the finished product does when diluted.As far as I know vinegar is not recommended for adjusting skin pH . Your first point doesn’t make any sense where you claim that citric acid make skin more sun burn sensitive. What FDA told about AHAs is , when you use these as exfoliating agents and with lower pH or as peelers , it may cause sunburn or photosensitive. The tiny amount of citric acid will not cause any sunburn . We always use NaOH to adjust pH though it is very harsh . Like NaOH Citric acid or lactic acid will not do anything when you use it as pH adjuster .
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It is meaningless to class acids or bases as “harsh”. When used to adjust pH they form harmless salts. Sodium hydroxide and chlorine, suitably combined, product table salt, a key item in our diet.
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Belassi said:It is meaningless to class acids or bases as “harsh”. When used to adjust pH they form harmless salts. Sodium hydroxide and chlorine, suitably combined, product table salt, a key item in our diet.
Balassi Sir , this is my point also , it is a neutralization reaction .
But in this thread Gunther claimed that if citric acid is used as pH adjuster it will cause Sunburn . Is citric acid really caused ‘ sunburn sensitive ‘ as he claimed if it is used as pH adjuster ? -
So the cir has a ridiculously long report on glycolic/lactic acid that somewhat relates. Honestly I haven’t read all of it but it seems to show that concentration and pH, in addition to the formulation method can prevent/mitigate AHA-related sun damage.
Ex:
“The increase in UV radiation damage associated with AHA pretreatment, therefore, was of such a magnitude that it is easily conceivable that
aspects of product formulation could eliminate the effect.”https://online.personalcarecouncil.org/ctfa-static/online/lists/cir-pdfs/pr34.pdf
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How about gluconolactone?
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Gluconolactone is not pH active. Gluconic acid would work.
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@Pharma - Gluconolactone hydrolyzes to gluconic acid in water.
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Yes, true, but hydrolysis is slow and it’s hence not useful for lowering pH to a given value. It will gradually lower pH during storage.
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In my experience the hydrolysis takes place within an hour. It is easy enough to begin prepping for formulation by making a stock solution. This is a fairly common albeit expensive acidulant in food and cosmetics.
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From PubChem regarding Gluconolactone:
3.2.10 pH
Freshly prepared aqueous solution has pH of 3.6, changing to 2.5 within 2 hours
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Interesting. I tried to reverse engineer Lotion P50 (which is basically gluconolactone, lactic acid, salicylic acid and a couple of useless extracts) and even at 8% in the water it only changed the ph from 7 to around 6. I haven’t checked 2 hours later but now I will.
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Two hours? Okay, that’s faster than I thought! Still, IMHO not practical.Also, gluconolactone is in equilibrium with glucuronic acid. Should glucuronic acid get ‘used up’ (neutralised), new one will form. That’s nice in case of an additive but complicates things with regard to maintaining a certain pH. Since we’re talking fancy/expensive acids, why not use gluconic acid or the like?
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Jeez! When comes to Glucono Delta Lactone, I am already an expert! Hahahaha! Oddly enough, what is inexpensive to you (all) is expensive to me, vice versa. I have plenty of GdL at my disposal!
Heat the solution! Need not rolling boil. Need not very hot. No “heat and hold for 20 minutes” nonsense. Heat it (GdL in water) up and the solution magically turns acidic quickly. Yes, quickly. Very, very quick. No more tens of minutes to hours of waiting. Not even a minute, depending on what you use to heat things up. I nuke mine in microwave or mini jet lighter.
Don’t believe me? Add some base like you would neutralise an acid or use some pH testing thing to ‘see’ the change. The magic is truly instantaneous. I do not seem to get bored repeatedly watching it as it happens.
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Interesting. I added it to cold water because it dissolves easily anyway. I will check again. I didn’t even consider it a true acid although it’s a PHA because it’s effect on pH was so minor.
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