cosmetic-pH

Article by: Kelly Dobos

Svante Arrhenius is credited with first elucidating the nature of acids and bases (he also gave us the Arrhenius Equation which factors into the use of increased temperature in formulation stability studies). His definition was a bit narrow and was later expanded on by two chemists for whom the current definition of acids and bases is named, Johannes Brønsted and James Lowry. By the Brønsted-Lowry definition, acids are proton donors and bases are proton acceptors. cosmetic-pH

The pH scale is a compact way to represent the acidity of a solution. The pH of a solution is the negative log of the hydronium ion (H3O+scale based on 10, the pH changes by 1 for every power of 10 change in hydronium ion concentration. A solution of pH 3 has 10 times the concentration a solution of pH 4 and 100 times that of a solution of pH 5. And because it is a negative log scale the pH decreases as hydronium ion concentration increases. The lower the pH of a solution, the more acidic it is. A pH of 7 is considered neutral and higher pHs are more basic.

One important thing to keep in mind is that measurement of pH is limited to aqueous solutions. Measurement of pH in alternate systems would require the development of new pH scales. Because of this, certain cosmetic formulations like water in oil creams do not have a pH but the pH of the water phase can be measured prior to emulsification or upon breaking the emulsion.

Why is pH Important for formulating Cosmetics?

The normal skin surface pH is slightly acidic and ranges between values from around pH 4 to pH 6. A study by Lambers et al. reported that the skin surface is close to an initial pH of 4.7, an average calculated from 330 subjects, showed virtually no change when the application of water or cosmetics was restricted for 24 hours. The skin surface pH can also vary by body site and can be changed significantly with the application of soaps, cosmetics or even rinsing with alkaline water.

Some of the most important anti-aging ingredients used in cosmetics treatments are alpha hydroxy acids. While the percentage of alpha hydroxy acid is important, the pH of the final product has a big impact on efficacy. Bringing a formulation to a more neutral pH decreases efficacy. However it can also be useful when formulating for sensitive skin types.

pH is also important to variety of other cosmetic ingredients including polymeric thickeners, dyes, and certain preservatives. So be sure to understand the pH limitations of individual ingredients and the overall formulation when developing cosmetic products.

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10 comments

  1. Rian DP

    Hai Kelly, can i ask you something, i wanna formulate a body lotion, can i make it with pH 7? because due to the stability of the active ingredient in my product i need to make it in pH 7, but as i know, skin pH is around 4-6 right, thanks for your time to read my comment and i would like to wait your response 😀

    1. Kelly
      Kelly

      You can certainly make a pH 7 lotion, the skin’s acid mantle is very resilient.

  2. Michael

    Dear Perry,

    When formulating a lotion for sensitive skin types, what is the optimal pH in your opinion (active ingredients nonwithstanding)?

    And with regards to sensitive skin, instead of AHAs (even those as mild as Mandelic Acid) what do you think of PHAs? Are they as effective in your opinion?

    Thanks!

      1. Michael

        Hey Kelly,

        Thanks for answering; sorry for the mixup. And thanks a lot for the link! 🙂 If you could, I’d really appreciate any input on the sensitive skin and pH. I want to formulate something with Vitamin C for those with sensitive skin and I can’t decide which because everything is pH dependent.

        1. Kelly
          Kelly

          Hi Michael
          Would not recommend low pH formulations for sensitive skin, after all one of the test methods used to assess sensitivity is called the lactic acid sting test. DSM makes a stabilized form of Vitamin C which is stable at pH 7 and converts into an efficacious form on the skin. You can get data sheets and more information about the ingredient here – https://www.ulprospector.com/en/na/PersonalCare/Detail/473/317173/STAY-C-50. Good luck with your formulation!

          1. Michael

            Thank you Kelly 🙂

            I really appreciate all the help and links!

            You rock!

  3. Fernanda

    Hi Perry and fellow readers!

    I’m very interested in formulating skin and haircare products and one of my main goals in life is to learn how to know exactly what a product is by reading only the INCI, so not cheating by looking at the packaging, marketing claims, front label and so on.

    I work in a cosmetics store and sometimes ask my colleagues to test me on this – and some systems are very easy to recognize from the active ingredients such as shampoos, antiperspirants, hair colors, depilatory creams, sunless tanners and nail polishes, but I’m having a hard time memorizing the connection and INCI-position of some other raw materials in the formulas, especially within the color cosmetics range.

    Obviously telling the difference between a hand and body cream is difficult, as well as a deep or normal conditioner which both basically have the exact same raw materials in the same order.

    Do you have any advice on how I can expand my formula memorizing skills, and do you know if there is any website where I can read only INCIs and try guessing what the product is?

    My friends and colleagues are quite tired of me asking them to quiz me since they don’t share the same geekiness or can’t read the small print or pronounciate the names. Thanks!

  4. Kelly
    Kelly

    Sure, you can formulate at higher pH levels. It really depends on the product and what you are trying to achieve.

  5. Nayaka

    Is it okay to formulate cosmetic with pH more than 6? For example, bar soap has pH around 10. Thanks.

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