Request for references for the pH of haircare products, esp shampoo

I recently got into a discussion with a (non-cosmetic) chemist about some things I'd previously thought were generally accepted facts regarding haircare formulation, specifically shampoo. That chemist challenged a lot of my knowledge, and I thought I'd get some more insights from a few pros, if anyone's willing! 

I've read numerous places that hair's natural pH is ~ 4.5–5.5, and that most hair products (unless you're trying to lift the cuticle for some reason) should be in this range, including shampoo. I've seen peer-reviewed articles that support this, but the chemist I was talking to pointed out that most of the articles I'd referenced were weak research (here's an example), and once they did that, I realized most of my references for hair and formulation pH don't seem to have any real studies attached.

I've spent some time hunting, but I'm having trouble finding studies that verify hair's pH (which... since hair is not a liquid, I'm unclear how that works?) and the ideal pH of haircare formulations. I feel like this research must exist since I've seen it referenced often in books, articles, etc., but I can't find it. Can anyone help point me toward studies about ideal pH for haircare products, and the pH of hair itself?

Comments

  • PerryPerry Administrator, Professional Chemist
    edited August 3
    Hair pH - Hair doesn't have a pH since it's a solid. It's more proper to talk about hair's isoelectric point. This is the "the moment of charge neutrality in a determined pH." Hair is made of protein so it has + charges and - charges. The isoelectric point is what some people erroneously call the hair pH. (The reference book for information about the properties of hair is The Chemical & Physical Behavior of Human Hair.)

    But even knowing the hair "pH" doesn't answer the question of what is the ideal pH of a haircare formulation. What do you mean by ideal? This is not an objective question. This is a subjective question. What does the question mean? Is it the ideal pH to have the least stinging eyes? The ideal pH to remove the most hair sebum? The ideal pH to leave hair in the best condition?  The ideal pH to have the least amount of breaking?

    Then you could add to that, ideal pH using which surfactant or surfactant blend? You could add what's the best pH for the condition of the hair or the shape of the hair.  There are no simple answers.

    Just think about it, if you were designing a study to determine which is the "ideal" pH for a shampoo, what study would you run? What characteristics would you measure? 

    The best we can do is to make some generalizations about what we think would be good. Shampoos with a pH range from 4.5 - 5.5 probably will be less irritating to the scalp so that seems like a reasonable range to shoot for. The cationic surfactants in conditioners probably will deposit better at a lower pH say 3.5 - 4.0. So, we formulate there. Maybe some system might work better at a higher pH? Who knows? You would have to experiment to find out. 

    I think what you are going to find is that there isn't a lot of (good) published research about many things related to cosmetics. There are a few reasons for this.

    1. Most "serious" scientists aren't interested in the subject. Cosmetic science is an applied science with little opportunity to make groundbreaking discoveries, so there is no incentive for university researchers to spend much time delving deep into the subject.

    2. Related to that, there is also not much money in terms of grants given to people to study the subject. And money that is paid usually comes from a big company like P&G or some raw material supplier who is specifically trying to prove something. Maybe an outfit like the Textile Research Institute may publish some basic hair research but they rely on customers who pay them to run studies. Much of what they discover they may not publish.

    3. It's a complicated subject. Many of the questions related to cosmetics are subjective ones. And that is the reality of all cosmetic research. The questions are mostly subjective and there are no simple answers to subjective questions.

    This is also why you can take most people's advice about characteristics of cosmetic products with a grain of salt. There are practically no universal rules when it comes to what makes the "ideal" hair care product. 

  • NoelleLopesNoelleLopes Member
    edited August 3
    Thank you Perry, I appreciate the in-depth reply! (I knew when I asked I was asking what's essentially a n00b question.) I also and especially thank you for the book rec — I've already ordered a copy.

    In your answer you've sussed out my internal bias, I said "ideal" when I really meant "the least amount of breaking" + "leave hair in the best condition" (in that order). You are of course right, cosmetic efficacy is subjective based on whatever a person's priorities are. 

    I was mulling over how I'd study the impacts of various pH of shampoo on hair this morning. I was thinking I could purchase virgin hair swatches, bleach some of them (to simulate damage) and use the rest as-is, and then test sub-groups of both bleached and non-bleached in shampoos of different pH — say, one acidic at 5, one neutral, and one alkaline at 8. They'd have to be washed and dried a number of times, and then tested for for breakage somehow. Or maybe just photographed under a microscope in comparison with the unwashed hair. This is, obviously, a *very* rough idea.

    I'm a nerd deep in my soul and I don't like not knowing the effects of the things I'm making, so I hope I find the time to do this! In the meantime, I'm happy to dig into the book. Thanks again for your input.
  • NoelleLopesNoelleLopes Member
    edited August 3
    I edited my original comment instead. Still learning how to use this forum. 
  • PerryPerry Administrator, Professional Chemist
    I empathize with your desire to have better answers for questions in cosmetic science. When I started in the industry, I was disappointed when I discovered how many questions didn't have good answers. And it was a bit disheartening to know how difficult it would be just to get an answer to what seems like a simple question. But I digress..

    Alright, now we're getting closer to something we can test, conditioning and hair breakage.

    If we stick with shampoo & we try to discover what is the ideal pH of shampoo to have the least amount of breakage?

    Here are things to consider...

    1. You can buy pre-damaged hair swatches. These would be better than damaging them yourself since the damage would be more uniform.

    2. You'll have to come up with a standard washing protocol including water temperature, pH, amount of shampoo, amount of time for wetting, rinsing, washing, and a washing technique (e.g. how to stroke the shampoo through the hair) plus a drying technique.

    3. You'll want to do a wider range of pH at first. Say 4.0, 7.0 and 9.0. Or maybe just test 4, 5, 6, 7, 8, & 9. You'll have to do multiple tresses at each pH.

    4. You'll need a method for counting broken hairs. Of course you'll have to decide if you comb the hair. If you do, you'll have to standardize this.

    5. You'll need a standardized shampoo. You'll want to start with the most simple shampoo you can make, so just surfactant and water. 

    6. You'll also need to do all this testing blinded so you don't bias your results.

    And after you've run this experiment, if you do find statistically significant results, the only thing you will have really learned is the optimum pH for the surfactant system you tested, on hair tresses of the hair you tested. This information may (or may not) be generally applicable. This information may not even be applicable to hair growing on a person's head, so the second phase of the study would have to involve a half-head salon test.

    Now, if you change the surfactant system, you'd have to re-run the test. If you add a conditioning agent to the shampoo like a cationic polymer or a silicone, you'll have to re-run the test. You quite likely will get different results.

    So you're still left with the question, what is the optimal pH for shampoo? Without testing a lot of different shampoos, you can't really say. This isn't even touching on the question of conditioners or other hair treatments.

    All this is to illustrate that getting answers to such questions can be complicated.
  • NoelleLopesNoelleLopes Member
    edited August 4
    Complicated, I can deal with. :) I don't want to make things awkward with superfluous thanks, but this is a very generous response so... again... thanks!

    Could you point me toward where I might purchase pre-damaged hair swatches? When I google "hair swatch testing" I keep getting returns about avoiding the detection of drugs in one's hair. Apparently, google thinks I like to party.
  • PerryPerry Administrator, Professional Chemist
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