Home Cosmetic Science Talk Formulating pH of Sunscreen lotion

  • pH of Sunscreen lotion

    Posted by vjay on December 17, 2013 at 7:05 am

    What is the standard pH of Sunscreen lotion / Fairness lotion where I am using Avobenzone, Octocrylene & Octyl Methoxy Cinnamate.

    I read some where that if we are using TiO2 so we have to maintain pH above 7.0 , I don’t know why ?

    vjay replied 10 years, 4 months ago 5 Members · 7 Replies
  • 7 Replies
  • Duncan

    Member
    December 17, 2013 at 5:00 pm

    For TiO2 the pH is due to the surface potential IIRC. Get the pH too off kilter and it can mess with the dispersion abilities and emulsion stability

  • alchemist

    Member
    December 17, 2013 at 5:40 pm

    Anywhere from 3.5 to ~7 depending on your formulation type and active.

  • ChemWizard

    Member
    December 25, 2013 at 8:26 pm

    @ Duncan, can you please explain surface Potential IIRC and how it effects stability?

    @ Vijay, In my experience the combinatin of ingredients you wokring with wold change the color of your batch into yellow, if the pH is higher than 7. And, on the other hand, SPF with Zinc and TiO2 below 7 has shown instabilities. 

    I am not sure whats the right explanation for that, but I am hoping Mentors and experts here would have something to say!

     

  • alchemist

    Member
    January 1, 2014 at 10:21 pm

    Very simply, if you look at the surface of TiO2 you’ve got a lot of oxygen atoms, that can react with either H+ or OH- .  So in a simple aqueous dispersion this means that at low pH the overall charge of the particles are positive, at higher pH the charge will be negative - at a certain pH the charge will be neutral so the particles will coalesce and the dispersion wont be stable.  The pH this occurs at is affected by the concentration and also any salts in the dispersion.

    In cosmetic products it gets a lot more complicated since the TiO2 is usually coated with Al2O3 and then something else depending whether you want a hydrophobic or hydrophilic grade.  

  • Chemist77

    Member
    January 1, 2014 at 11:25 pm

    @ChemWizard Surface potential has been explained by alchemist and IIRC is short for If I Remember Correctly, hope that makes life a bit easier  :)

  • ChemWizard

    Member
    January 7, 2014 at 10:31 pm

    lol that really helps Milliachemist and Alchemist:)

  • vjay

    Member
    January 8, 2014 at 3:20 am

    thanks to all of you.

    I will remember it.

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