Home Cosmetic Science Talk Formulating Acids reacting with clays

  • Acids reacting with clays

    Posted by Nihed on February 23, 2022 at 5:45 pm

    Hi everyone hope you are doing well,

    I have a little problem, today I tried to formulate an exfoliating face mask using kaolin and pink clay with and lactic acid as an exfoliant.

    I prepared my water phase ( water,glycerine, LA, preservative) and adjusted the PH to around 3.6. As I started incorporating my clay mix, it started foaming and producing a very bad smell, the formula became a mess.

    I didn’t know that acids can react with clays
    to detect the problem I mixed separately :
    kaolin + LA = foaming smelly mess
    Kaolin + citric acid = foaming smelly mess( I though that maybe the problem was with lactic acid so I tried citric even though it’s not considered as an exfoliant) 
    I did that too with green clay and same results

    But the pink clay didn’t react with the acids whether I mixed it with LA or CA, there was no foaming.

    -I’dd like to know the science behind it. how come the kaolin and green reacted with those acids and not the pink clay ?
    -How can I make an exfoliating mask using clays and acids together ?
    -Will it do the same thing with salicylic acid?

    thank you in advace!


    Nihed replied 1 year, 11 months ago 4 Members · 5 Replies
  • 5 Replies
  • emma1985

    February 26, 2022 at 4:59 am

    I had a similar experience when I used Sodium Bicarbonate to adjust pH in my Lactic Acid mask that contains Pink Kaolin.

    I had much better results using Triethanolamine, are you using Sodium Bicarbonate by any chance?

    I still get a bit of the scent though, so I only use 1-2% clay.

    There are tons of commercial products on the market that contain AHAs and clay, so I don’t think there’s anything fundamentally wrong with combining them. But I could be wrong.

  • Nihed

    February 28, 2022 at 9:46 pm

    I used a solution of sodium hydroxide to adjust the PH ,but I’m positive that it’s between the clay and the acids.
    Just as I started to incorporate the clay mix to the water phase everything started foaming and the scent was very bad .
    In order to see what was wrong,I mixed saparatly each clay with lactic acid. The kaolin started foaming but not the pink clay I also did the green clay just to see if it was going to react or not, it did.
    here is some pics 

    first pic is when I added the clays to the water phase

    second pic : kaolin + lactic acid

    third pic : pink clay + lactic acid 

    I did the same replacing the lactic acid with citric, and same results .

  • bill_toge

    March 1, 2022 at 11:07 pm
    does it smell like rotten eggs?
    if so, it sounds like your kaolin contains a lot of sulphur
  • gordof

    March 2, 2022 at 8:07 am


    I would say that clays/Kaolin are a various mixture of different Chemical Bondings depending on the digging sight there can be various impurities like CaCO3 or Sulphers, even if the main Part is Kaolin. Some of the Clays you can get (not sure about the ones you described) have parts of lime (CaCO3) incorporated. They can react with acids and set free CO2 and therefore lead to Foaming of the Formulation. there is although the possibility that other Parts of the clay can make an Acid Reaction due to the very high surface area of the Clay the Reaction energy can be Reduces maybe setting free some more Smelly parts like sulfur (you can check if the Gas that is set free is Flamabell or not. if so and it smells like rotten eggs it is properly Supherhydrogen that is set free.

    In this case, I would check with the supplier and ask if they can give some advice about it. They Propoply have tested this scenario or you will not be the first one to do so they may have a solution for it you can go for. Be aware that if the gas is flammable it is a high risk for Production with this grade of Clay.

    Otherwise, you can just switch suppliers and see if you can find one that does not have this problem like obviously the Pink clay you have. 

  • Nihed

    March 3, 2022 at 8:54 pm

    @Bill_Toge @Gordof thank you for your answers !

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