Does skin and scalp have positive charge or negative charge?

AbdullahAbdullah Member
edited October 2021 in Formulating
Hair has negative charge and ingredients with positive charge attach to it better. What is the charge of scalp and skin of hand or face? 

Comments

  • PerryPerry Administrator, Professional Chemist
    It's a bit pedantic but it's not exactly right to say hair has a negative charge. For example, you can cause a positive charge by rubbing your hair on something like a hat or balloon or something.  

    The isoelectric point of hair is negative which is why positively charged compounds stick to the surface better.  The isoelectric point of skin is https://pubmed.ncbi.nlm.nih.gov/11166421/ is about pH 4.8 which would indicate that it too has an overall negative charge. 
  • @Perry thanks 

    What about scalp? 

  • PerryPerry Administrator, Professional Chemist
    @Abdullah - I can think of no reason it would be different than other skin.

  • Thanks Perry
  • @Perry can I ask a question!

    Does isoelectric point mean a pH that pHs above that has negative charge and below that has positive charge? 

    For example isoelectric point of skin is about 4.8. does it mean at pH below 4.8 like pH 4 the skin will have positive charge and at pH above that like pH 5.5 the skin would have negative charge? 
  • PerryPerry Administrator, Professional Chemist
    Not exactly. You see solids like skin and hair don't actually have a pH. Only solutions have a pH by definition. When people say hair or skin have a pH what they are really talking about is the isoelectric point. 

    Isoelectric point is the pH at which the hair will not migrate in an electric field.

    The pH of the surrounding solution doesn't actually change the positive or negative characteristics of the hair (or skin). It just says that if you want stuff to stick to your hair (or skin) having a positively charged ion in a lower pH solution is what you want to do.
  • It always have both charged sites at the same time, just one of them being (could be a lot, could be a little) more predominant.
  • @Perry so these surfactants will stick better to skin at which pH?

    Cationic surfactants at pH pH 5.5 or 4?

    Anionic surfactant at pH 5.5 or 4?

    Or does anionic surfactant stick to skin by electric charge at any pH or not at all? 
  • @zetein how? Can you explain a bit! 
  • @zetein thanks a lot.

    Can you tell me the name of this book please
  • Does this mean anionic surfactants work better at lower pH? 
  • SylSyl Member
    @Abdullah, It is a journal (magazine article) the page title says Journal of the society of cosmetic Chemists.
    @ Oladoo, it says that anionic surfactants interact more with proteins at low PH. That may be a potential for more irritation, more studies are needed.
  • PharmaPharma Member, Pharmacist
    Oladoo said:
    Does this mean anionic surfactants work better at lower pH? 
    The job of a surfactant is usually cleaning and that does not include binding to host molecules. So, no, the publication only illustrates the interactions of surfactants and hair/skin. Cleaning commonly refers to reduced surface tension and mechanical removal accelerated by surfactant-dirt interactions and, to a lesser degree, reducing dirt-hair/skin interactions. True, surfactant-hair/skin intaractions will play a role there and so does swelling but that's probably the least interesting effect when it comes to cleaning.
    Though when you're talking hair conditioning, things look different. There, the term surfactant is usually not used in cosmetics even if the employed molecules follow the exact same rules and will show the exact same interactions ;) .
  • @Pharma so surfactant like SLS from Shampoo will not attach and remain on skin or hair even if the pH of product is low for example 3 or 4, am i correct? 
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