Is a PH of 7-7.5 okay for a tonic?

DaveStoneDaveStone Member
edited August 2021 in Formulating
I read most are around 5.5. Is that to be in coordination with the skin's natural PH, or because it absorbs better at lower PH?
Say in the example formulation:
Distilled Water 90.5%
Niacinimide 3%
Propanediol 3%
Sodium Lactate 3%
Liquid Germall Plus 0.5%

Comments

  • There can be several factors. One being it closer to skin pH, another being the required compatible pH range of all your ingredients, lastly for functionality purposes.

    Normally there is a purpose why your pH requirement is at where it is, and it's up to you to justify your choice.  
  • PerryPerry Administrator, Professional Chemist
    George says that the optimal pH is 6.0 for Niacinamide. 
    https://knowledge.ulprospector.com/294/pcc-benefits-niacinamide/

    I don't know if I agree but he may have looked into the subject more than me. I do know that I've never seen any real data that shows matching the "skin's natural pH" has any impact on the performance of anything. It's just a marketing gimmick as far as I'm concerned.
  • DaveStoneDaveStone Member
    edited August 2021
    Perry said:
    George says that the optimal pH is 6.0 for Niacinamide. 
    https://knowledge.ulprospector.com/294/pcc-benefits-niacinamide/

    I don't know if I agree but he may have looked into the subject more than me. I do know that I've never seen any real data that shows matching the "skin's natural pH" has any impact on the performance of anything. It's just a marketing gimmick as far as I'm concerned.
    Yeah, I read you don't want to go below 5.5-6 for niacinamide...though I've found no information on what the highest PH limit is for it. I don't know what would happen at 7.5
    I would assume a ph below 5 or above 8 would be bad for your skin in a leave-on product. It seems most mass-produced toners/lotions are formulated at 5.5-6. Just like syndet bars, such as Dove, are formulated at around the same PH.
  • GraillotionGraillotion Member
    edited August 2021
    Paprik said:

    Agreed!...I take all my formulas (which include B3) to 5.5-5.9.  The sharpest chemist in the drawer...confirmed this was absolutely fine.  Granted I top out at 2%, and I believe that was under consideration with his recommendation.

    You need a LOT of time, heat, and a strong acid to create a negative in this pH range.  See the blurb I pasted below:

    The paper that I am referring to is called “Rate Studies on the Hydrolysis of Niacinamide” and they were using hydrochloric acid to perform the experiment in the acid region (which is all we care about here).  This is a significant detail as hydrochloric acid is a strong acid whereas AHA’s are weak acids.   Acid strength is not just about how much you put in a formula – 10%, 20%, 2% etc – it is also about how readily the acid let’s go of its hydrogen ion – its dissociation constant.  Strong acids completely dissociate in water meaning that even at low % concentrations the acid is quite potent. Weak acids have only a tiny part of themselves raring to go meaning that even at high concentrations they won’t be quite so aggressive.   The above study found that a 10% Niacinamide solution heated to around 89C and then taken to a pH of below 4.5 with a STRONG acid did start to hydrolyse and form Niacin and that this conversion was a first order reaction which basically means it went from Niacinamide to Niacin without turning into anything else first.  The study found that between pH 4.5-6 very little of this crazy game of shape shifting occurred.  In fact at pH 4.5 – 6 the half-life of the solution was found to be 1000 days which probably means that the average cosmetic formulator has little to worry about.
  • Mfg's have to write SDS's for the complete idiot.  They have no idea how someone will use their product....so they err to the cautious side.

    I can only imagine what the SDS is for water.  ;)

  • Honestly, Niacinimide is pretty much overrated. Fair & lovely's been using it since before I was born. 
    pH 5-5.5 is to claim pH balance when pre-sale regis is needed in EU and it's good for marketing.
  • GraillotionGraillotion Member
    edited August 2021

    I can only imagine what the SDS is for water.  ;)

    Well...I was half way kidding.... but I did find the SDS for water!  :D

    Looks like California did not find it as posing a risk...so I guess we're all OK.

    https://fscimage.fishersci.com/msds/89955.htm#:~:text=Deionized Water ACC%23 89955 Section 1,23751628%2C 25065%2C 57084%2C 57084A Synonyms%3A Company Identification%3A

    If you spill it, follow these guidlines (per SDS):

    General Information: Use proper personal protective equipment as indicated in Section 8.
    Spills/Leaks: Absorb the liquid and scrub the area with detergent and water.

    And if first aid is required (per SDS):

    Eyes: If irritation develops, get medical aid.
    Skin: Get medical aid if irritation develops or persists.
    Ingestion: Get medical aid if irritation or symptoms occur.
    Inhalation: Get medical aid if cough or other symptoms appear.
    Notes to Physician: Treat symptomatically and supportively.

    And last but not least....if you live in the EU:

    Safety Phrases:
    S 24/25 Avoid contact with skin and eyes.
  • Ooops...typo... Just read my first comment.... It should have read....I take all my formulas to 4.5 to 4.9.
  • I usually make sure it's less than 7 but I only go based on what is required out of the ingredients and especially the preservative. I see a lot of consumers who test the pH of their products and then decide whether the product is good or bad based on just that when in reality they have no idea why as a chemist we even care about pH. Whenever a consumer asks me to talk about pH I consider it something for the chemist to know and not for the consumer but of course it's been made into a marketing story as if we haven't been using exfoliating acids or bar soap forever now...


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