Comments

• jemolian Member

  January 2021

  Since you are using aloe vera, you might want to add a chelating agent, though you would also want a more robust broad spectrum preservative besides from the diols you have. 
  
  You would also need a buffer for the urea since it will increase the pH as it causes pH drifting over time. 
• ngarayeva001 Member

  January 2021

  You need chelating agent anyway as part of your preservative system speaking of which, I understand you rely on diols here. I am no expert by any means, but it doesn’t look sufficient to me especially with aloe added (aloe introduces additional preservation challenge). Other than that, your toner looks ok to me. I make a serum very similar to this (urea, niacinamide, sodium lactate, lactic acid, other humectants). I keep ph at 6 and thicken it with high molecular weight hyaluronic acid.
• jessicalerner Member

  January 2021

  This is super helpful. Thanks so much.
• Perry Administrator, Professional Chemist

  January 2021

  Yeah, you need a proper preservative and a chelating agent (like disodium EDTA)

  Learn to formulate cosmetics
• AbbasMo Member

  January 2021

  jemolian said:

  Since you are using aloe vera, you might want to add a chelating agent, though you would also want a more robust broad spectrum preservative besides from the diols you have. 
  
  You would also need a buffer for the urea since it will increase the pH as it causes pH drifting over time. 

  Hi, I made a toner and used urea in that. I have a problem with pH instability, I need help to form a urea buffer.
  Can I use tetrasodium edta instead disodium edta? because I have other acidic ingredients and need increase pH and adjust it in 5 around.
  thanks a lot
• jemolian Member

  January 2021

  For the buffer, you can see if the info here helps
  

  • https://www.researchgate.net/publication/264091890_Stability_of_urea_in_solution_and_pharmaceutical_preparations
  • https://patents.google.com/patent/US4672078A/en
    
  • https://pdf4pro.com/view/urea-from-the-chemist-s-point-of-view-247112.html
    
• Pharma Member, Pharmacist

  January 2021

  You can use whatever form of EDTA you like because, once you adjusted pH, they will all become the same.

  The optimal pH for urea is 6.2. In theory, you'd need a buffer which has a pKa between 5.2 and 7.2. Upon degradation, urea tends to increase pH which means a buffer with a pKa of 5.2 will not work. Therefore you're limited to buffers in the range of pKa ~6 to ~7.2. Notably, you'd need quite a bit of buffer... use something well tolerated. Good's buffers can come in handy.
  

  One trick which can work (I guess mostly if combined with a buffer) is triethyl citrate or triacetin. These will hydrolyse if pH rises and thereby release acids which lower pH back.
  
• AbbasMo Member

  January 2021 edited January 2021

  jemolian said:

  For the buffer, you can see if the info here helps
  

  • https://www.researchgate.net/publication/264091890_Stability_of_urea_in_solution_and_pharmaceutical_preparations
  • https://patents.google.com/patent/US4672078A/en
    
  • https://pdf4pro.com/view/urea-from-the-chemist-s-point-of-view-247112.html
    

  Thanks a lot