pH of Sunscreen lotion

vjayvjay Member
edited December 2013 in Formulating

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 ?

Comments

  • DuncanDuncan Member, Professional Chemist
    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
    UK based, Over 20 years in Toiletries, After a 5 year sabbatical doing cleaning products, back in the land of Personal Care
  • Anywhere from 3.5 to ~7 depending on your formulation type and active.


  • @ 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!

     

  • 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.  


  • Chemist77Chemist77 Member, PCF student
    @ChemWizard Surface potential has been explained by alchemist and IIRC is short for If I Remember Correctly, hope that makes life a bit easier  :)
  • lol that really helps Milliachemist and Alchemist:)
  • thanks to all of you.

    I will remember it.

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