Home Cosmetic Science Talk Formulating Natural Soap with a PH of 4.5 to 5.5?

  • Natural Soap with a PH of 4.5 to 5.5?

    Posted by Anonymous on June 5, 2016 at 8:09 pm

    I am really in need of some assistance. I am in no way a scientist but a “hobbyist” natural soapmaker for more than 15 years. I have done a lot of research in order to formulate my own recipes for soaps, serums and such. I have been approached by someone to formulate a natural soap with a PH of between 4.5 - 5.5. To be labelled a 100% natural bar soap with a Ph the same as the skin.

    In my experience, oils and butters saponified with NaOH and/or KoH, even with a relatively high superfat of 8%, it is impossible to achieve this low a Ph in a natural soap. I have been able to lower the Ph slightly with the addition of citric acid at 1,5%, and lactic acid, but never in the region of what is required. I have tried including the additives in a rebatch, after the cook in Hot process and in cream soap, but I cannot get the Ph low enough.
    This person has the following qualifications;
    BSc(Biol Sc), MSc(Applied Human Nutrition), Somatology, and is confidant that this can be achieved without the use of any chemical substances.

    With all my research the only thing that comes I can find is a cleansing creams or lotions, but not a natural soap.

    Any advice or clarification on this will be appreciated.

    Anonymous replied 7 years, 9 months ago 6 Members · 10 Replies
  • 10 Replies
  • belassi

    June 5, 2016 at 9:21 pm

    It is absolutely impossible. The person’s qualifications do not include chemistry, which is the relevant knowledge here.

  • microformulation

    June 5, 2016 at 10:29 pm

    Also I would even be impressed to see how you would do anything, even make the soap base without using “any chemical substances.”

  • crisbaysauli

    June 6, 2016 at 4:02 am

    @Microformulation thank you for pointing that line out. I’ve been reiterating this countless times. Lots of marketing people declare “chemical-free” products, but come to think of it, even water is a chemical. 

  • mikethair

    June 6, 2016 at 4:06 am

    In my opinion and experience as a professional  soap maker, soap made using saponified oils/butters could not achieve a pH of 4.5 - 5.5.

    My approach would be to ask the client the parameters for defining “natural” soap, perhaps they are not thinking about traditional cold-process soap? Perhaps some Angel Dusting and Greenwashing a SYNDET with a pH of 5 would keep them happy?

    Also, ask why the need to be the same pH as skin. Fact of the matter is that soap is more effective as a cleanser at a higher pH, which is in effect the function of soap. The skin can recover back to normal pH fairly quickly without any ill-effects.

  • microformulation

    June 6, 2016 at 5:03 am

    Under what objective standards can you say that a soap is a more effective cleanser at high pH? I agree that in intact, healthy skin the effects of the higher pH are negligible, but that doesn’t speak to efficacy, Could you cite a credible and documented Journal citation supporting that it is “more effective” and how?

  • bobzchemist

    June 6, 2016 at 1:25 pm

    I know for an (unpublished) fact that “natural” soap is more stable at higher pH, but we’ve never seen any indications that it performs better in any way. I think this may be one of those cases where someone said that natural soap is “better” at higher pH, without specifying what “better” meant. Unless…if you made a soap that was incompletely reacted at lower pH, a higher pH of the same formula would mean more actual soap in the product, which would then clean better.

    Things that make me go hmmm…Mike, do you have any more details?

  • microformulation

    June 6, 2016 at 1:39 pm

    No offense to anyone, but in order to be more subjective I request unbiased proof. A logical fallacy is to lead with an untrue or proven fact, presenting it as fact and hence implying that it is an unassailable fact and then use this fact to support an argument. In all practicality the entire argument is built on sand and hence invalid. Unfortunately this logical fallacy is common in our Industry.

    That said, perhaps in some way it is better. So I guess the challenge is to a. define objective, measurable and reproducible ways in which it is better. I see Bob’s point and I apologize if I misunderstood. My assumption is that you are asserting that a soap at a high pH is more effective than a surfactant cleanser at a pH of 4.7 or so.

  • markbroussard

    June 6, 2016 at 1:47 pm


    “This person has the following qualifications; 
    BSc(Biol Sc), MSc(Applied Human Nutrition), Somatology, and is confidant that this can be achieved without the use of any chemical substances.”

    If this person is so confident that it can be done and they have these “impressive” credentials … Don’t you find it interesting that they are not doing it themselves?

    Simply tell your client that what they are asking is not possible.

  • bobzchemist

    June 6, 2016 at 6:09 pm

    @MagicM there is a chemical reason why this can’t/won’t work, and I hope I can explain this well enough for you to explain to your client.

    Chemical reactions come in two types, reversible and (normally) irreversible, Polymers are an example of an irreversible reaction - once formed, you cannot normally break a polymer back up into it’s individual monomers. (You can break it down into individual atoms, but that’s a different discussion)

    “Natural” soapmaking, however is a (somewhat) reversible reaction. Fats/oils used in soapmaking are triglycerides - they have one molecule of glycerin attached to 3 molecules of fatty acids. When you expose an oil (triglyceride) to a strong base, you first get a hydrolysis reaction, which breaks the triglyceride up into its component parts. This is the irreversible part of the reaction - you won’t get the glycerin to attach the 3 molecules of fatty acids again (except under extraordinary circumstances). 

    Now, we get to the saponification part of the reactions. The three fatty acids are neutralized by the base (sodium or potassium hydroxide), forming ionic compounds. These compounds are what we call “natural” soap - the glycerin is irrelevant - it may or may not be left in the soap. This reaction is the part that’s easily reversible, and it is entirely dependent on pH. Below an apparent pH of about 8.0 or so, the reaction starts to reverse, leaving you with fatty acids and neutralized base that does not clean at all. So, it’s just chemically not possible for your client to have a “natural” soap at a pH of 4.5-5.0, because at that ph, soap cannot exist.

    How can you compromise? Well, soap bars (as opposed to liquid soaps) don’t have an actual pH, because they don’t contain water. The “apparent” pH only shows up when you’ve dissolved the soap in water, typically at a 10% concentration. Now, you can use this to play a chemical trick - it’s barely possible to mix enough powdered acid, citric, for example, into your soap bar, at a point where it won’t interact much with the soap, so that when you dissolve the soap into water to measure the pH, you get a pH of about 7, which is neutral. If you can’t sell this to your client, you’re going to have to use surfactants other than soap.

  • Anonymous

    June 6, 2016 at 8:11 pm

    Thank you everyone for this vital information. I am not qualified to debate against scientists, but through my research and experience I have learned that my task was an impossible one. I apologize for my choice of words which may have been incorrect, but thank you for understanding what I was trying to say. I am so grateful to all of you for your professional input, and because of all your qualifications, it will assist me greatly to relay the facts without undue argument. Thank you again.

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