Lower PH for soap bars

Hi, can you please help making suggestion on what can I use to lower PH for soap bar that doesn't effect the hardness of the bar (I tried critic and lactic acid, it sure didn't work as it soften the bar)

I currently got PH of 7-8 and would like to lower it to 5-6 please.

Please noted that this is a facial bar, that's why I want lower PH than usual bar use for body.

Thank you for your help


  • If you lower pH of a soap it will stop being a soap. It will separate.
  • Bill_TogeBill_Toge Member, Professional Chemist
    yes, you need to use a different kind of surfactant to create lower-pH soap
    Dove is a textbook example; it's formulated at neutral pH, and its principal surfactant is sodium lauroyl isethionate
    UK based formulation chemist. Strongest subjects: hair styling, hair bleaches, hair dyes (oxidative and non-oxidative) I know some stuff about: EU regulations, emulsions (O/W and W/O), toothpaste, mouthwash, shampoos, other toiletries
  • Agree with Bill_Toge. Dove is a syndet bar, not a soap. If you want to make a low pH bar without decreasing pH, use SCI, SLSa and CAPB as your surfactants. This combination would have a pH around 6. If you want it to be sulfate free (although SLSa is rather mild) replace SLSa to powdered olefin sulfonate, but that type of bar takes a while to harden.
  • Thank you, maybe I am using a wrong choice of word. I think what I am doing can be called syndet bar. My main sufactant is SCI but I used sodium stearate (12%) to form a bar so with that my PH goes up to 7-8. Please also noted, no other ingredients I used hashigh PH, only sldium starate seem to be a cuased of the problem

    I only used 10% of SCI as this is the bar for facial so I wanted it to be mild. Any suggestion how can I reduce PH even further?

    Thank you!
  • If not using sodium stearate is there other ways to form a bar that produce low PH?

    Thank you!
  • GuntherGunther Member
    edited April 9
    The problem is that lowering pH causes the soap to revert to the free fatty acid.

    Na-CH2-(CH2)n-CH3 (Sodium soap)  +  C6H8O7 (citric acid)  --->  H-CH2-(CH2)n-CH3 (free fatty acid)  +   Na3-C6H5O7 (Sodium citrate)

    As you know free fatty acids aren't soluble in water, nor they clean as soaps do.
    For lower pH levels, you'd need synthetic surfactants because they don't decompose.
    Sulfates, sulfonates, sarcosinates, isethionates cling to the Sodium atom "tighter" than soaps do. And in nonionic surfactants there's no Sodium (or Potassium) atom to be lost.
    Hope this helps.
  • @Gunther, thank you for your input. However, I just mentioned it was my mistke using wrong word. I'm actually doing syndet bar not soap. But PH level still high as mentioned in previous replied.

    Do you have an suggestion?

    Thank you!
  • My advice is to get a Shampoo Bar e-zine from swiftcraftymonkey. She explains in details how to make syndet bars of all kinds.
  • GuntherGunther Member
    And get rid of Sodium stearate and all soaps, they will always have a high pH.
  • @Gunther if I get rid of sodium stearate, what do I use to form the bar then? Thank you for your help.

    @ngarayeva001 thank you!

  • GuntherGunther Member
    @Gunther if I get rid of sodium stearate, what do I use to form the bar then? Thank you for your help.

    @ngarayeva001 thank you!

    Some synthetic surfactants can harden the bar on their own,
    but you'd better check swiftcraftymonkey (paid) website for in depth details.
  • @Gunther thank you!
  • @MayDay1988
    INCI %
    Sodium Lauroyl Methyl Isethionate (power) 44.0%
    Sodium C14-16 Olefin Sulfonate (powder) 35.0%
    CAPB 17.0%
    Sodium Lactate 3.0%
    Germaben II 1.0%

    An example of sulfate-free syndet. Swiftcraftymonkey has more interesting formulas.
    Disclaimer: nothing is wrong with sulfates. This is just something I am working on now. The purpose is to give you an idea about the proportion of dry ingredients.
  • @ngarayeva001 ; thank you so much! I'll register the website and learn more. As my 2 problems now are I don't want to put too much surfactants in the formula because it is for facial (want to make it mild) but at the same time if not enough sufactant or powder the bar will be soft.

    Thank you!
  • Face wash should be formulated with 8-10% of surfactants. You can’t make a bar product with such a low concentration of surfactants. Experiment with stearic acid as a filler I guess. 
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