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-acids

Any non alpha hidroxy acid suggestions?
I'm leaning heavily towards acetic acid.
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Comments

  • PerryPerry Administrator, Professional Chemist
    Phosphoric acid
    Hydrochloric acid

  • AzizAziz Member
    Perry said:
    Phosphoric acid
    Hydrochloric acid

    Is using HCl in cosmetics safe ? 
  • PerryPerry Administrator, Professional Chemist
    @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.
  • AzizAziz Member
    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 ?
  • MarkBroussardMarkBroussard Member, Professional Chemist
    Phytic Acid
    Chemist/Microbiologist formulating in the Organic & Naturals arena under ECOCert/Natural Products Assn/Whole Foods/National Organic Program guidelines focused skincare & haircare products. 

    See website for details www.desertinbloomcosmeticslab.com
  • PerryPerry Administrator, Professional Chemist
    @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.

  • 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
  • PharmaPharma Member, Pharmacist
    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.
  • ozgirlozgirl Member, PCF student
    What are you using in your cream that it needs that much pH adjustment?
  • AzizAziz Member
    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 . 
  • 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.
    Cosmetic Brand Creation. Concept to name to IMPI search to logo and brand registration. In-house graphic design inc. Pantone specs. Cosmetic label and box design & graphics.
  • AzizAziz Member
    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
  • @Aziz @Belassi Sodium hydroxide would look nasty on a label.
    Even if harmless, tiny amounts are used, customers would perceive it as harsh.

    So do strong mineral acids.
    Hence my question.
  • How about gluconolactone? 
  • PharmaPharma Member, Pharmacist
    Gluconolactone is not pH active. Gluconic acid would work.
  • @Pharma - Gluconolactone hydrolyzes to gluconic acid in water.  
  • PharmaPharma Member, Pharmacist
    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.
  • 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. 
  • MarkBroussardMarkBroussard Member, Professional Chemist
    From PubChem regarding Gluconolactone:

    3.2.10    pH

    Freshly prepared aqueous solution has pH of 3.6, changing to 2.5 within 2 hours

    Chemist/Microbiologist formulating in the Organic & Naturals arena under ECOCert/Natural Products Assn/Whole Foods/National Organic Program guidelines focused skincare & haircare products. 

    See website for details www.desertinbloomcosmeticslab.com
  • 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.
  • PharmaPharma Member, Pharmacist
    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?
  • 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.
  • 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.
  • Cst4Ms4Tmps4Cst4Ms4Tmps4 Member
    edited November 3
    @ngarayeva001
    It is very soluble in water! I do not know how soluble it is but I manage to make a solution of it, 60g or 60% in water. I do not know where you live, for me is easy for it to be dissolved due to the high 'room temperature' here.

    Many Asians making (silken) bean curd had long replaced Citric Acid and Boric Acid with GdL. Without scientific data they learnt that it has something to do with heat. Not only it is far less sour than other acids (at the same gramme), but also makes the smoothest and most even bean curd because GdL can be properly mixed in and the soybean milk has chance to rest and stay still while proteins are being coagulated. With Citric Acid the result is nearly instantaneous regardless of temperature, bean curd like this is gritty, uneven, and if 'unlucky' it tends to and prone to oozing liquid (syneresis).

    I presume you tested pH while it is not completely turned to its acid form. GdL is slightly sweet! I do not mean sweet as an expression, it is truly sweet. Taste it! Very soon it turns sour. I assure you, its pH is proper low once its devilish side of metamorphosis is complete. Depending on concentration, it will start to sting your eye, wound, etc. Oh, also depends on concentration, pH is low enough to make your eyes squint and make funny faces. I guess the latter is the best evidence!   :D
  • @Cst4Ms4Tmps4, I'm interested in your experience with Glucono Delta Lactone. Do you then ever use it in place of Citric Acid in skincare? Would it also improve the smoothness of an emulsion in the same way that it does for the bean curd?

    In heating, do you heat the GdL in water separately before adding to the rest of the formula? How hot does it need to be heated to get the nearly instantaneous acidification that you mention?

    Does the pH drift for some time after in a formulation?

    Thank you!
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