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  • Sodium bicarbonate/baking soda irritation

    Posted by Minichemist6 on July 15, 2021 at 7:43 pm

    Hello,

    I am new here but I really need help! I believe this forum might be the solution because here are many people knowledgeable in the chemistry behind the cosmetic.

    This year I had an internship at a small company for natural cosmetics and my project was to find an alternative deodorant formulation without baking soda as some customers get rashes, itches etc (although it isn’t an allergen). Online I found that other companies use magnesium hydroxide as a deodorising agent instead of baking soda. As of now I do have some positive feedback from customers.

    Now onto my problem: as I have to write a report on it, I was looking for resources (preferably papers, books, journals) about why baking soda causes these irritations on the skin. Of course the high/alkaline pH-value might be the reason but the deodorant with magnesium hydroxide is also alkaline. The only difference between these two is that baking soda is water soluble.

    I would be grateful if someone could give me a good explanation why some people’s skin get irritated coming into contact with baking soda as well as a source supporting that explanation.

    Minichemist6 replied 3 years ago 4 Members · 8 Replies
  • 8 Replies
  • suswang8

    Member
    July 15, 2021 at 8:59 pm
    Blind leading the blind, but:
    I am not sure if this is only an issue with underarm deodorant, or other products potentially?  Do you know?  If only underarm deodorant, then one possibility is that this is a semi-abrasive powder, and the “friction” would lead to irritation in those with sensitive skin.

  • Minichemist6

    Member
    July 16, 2021 at 12:37 am

    suswang8 said:

    Blind leading the blind, but:
    I am not sure if this is only an issue with underarm deodorant, or other products potentially?  Do you know?  If only underarm deodorant, then one possibility is that this is a semi-abrasive powder, and the “friction” would lead to irritation in those with sensitive skin.

    As of right now I don’t know if it’s only an issue in the armpits (and where else sodium bicarbonate is used in cosmetic) but I can tell you that the alternative deodorant with magnesium hydroxide has the same consistency as the one with sodium bicarbonate and tester weren’t experiencing any irritation even when it was extremely hot or they exercised. So I assume friction is not the reason.

  • suswang8

    Member
    July 16, 2021 at 2:45 am
    That would lead me to two questions:
    -1-  When you say mag. hydroxide has the same consistency….how closely have you studied this?  I mean, you would really have to have looked at these very closely — perhaps under a microscope — to know whether one particle/grain was more abrasive than the other (when subject to friction).
    -2-  How many testers are you speaking of?  Sodium bicarbonate is only problematic in a relatively small percentage of people, so in my view, I think you would need to have had 20+ testers test it for a week straight before being confident it was truly not irritating.
    Someone online is claiming that it might be due to the alkaline nature of sodium bicarbonate.  I guess the particles “cling” to your skin, and the pH imbalance is enough to give you irritation — perhaps it’s worse in people whose skin is slightly more acidic than others’? 
  • Abdullah

    Member
    July 16, 2021 at 5:55 am

    What are the complete list of your ingredients, what amount each and what is the final pH. 
    That way we can know what is happening.

  • Minichemist6

    Member
    July 16, 2021 at 6:40 pm

    suswang8 said:

    That would lead me to two questions:
    -1-  When you say mag. hydroxide has the same consistency….how closely have you studied this?  I mean, you would really have to have looked at these very closely — perhaps under a microscope — to know whether one particle/grain was more abrasive than the other (when subject to friction).
    -2-  How many testers are you speaking of?  Sodium bicarbonate is only problematic in a relatively small percentage of people, so in my view, I think you would need to have had 20+ testers test it for a week straight before being confident it was truly not irritating.
    Someone online is claiming that it might be due to the alkaline nature of sodium bicarbonate.  I guess the particles “cling” to your skin, and the pH imbalance is enough to give you irritation — perhaps it’s worse in people whose skin is slightly more acidic than others’? 

    1. Well we didn’t look under a microscope to compare both deodorants and there might be very fine differences since magnesium hydroxide is a finer powder than sodium bicarbonate but the end product does feel similar on the skin.

    2. As of now I don’t know how many testers my supervisor contacted and we are still waiting for more feedbacks but we did explicitly ask for people who get irritation from the deodorant with sodium bicarbonate. They should have been testing the one with magnesium hydroxide for about a month.

    Yeah I read something similar but I can’t find any sources that would support that claim :/

  • Minichemist6

    Member
    July 16, 2021 at 6:54 pm

    Abdullah said:

    What are the complete list of your ingredients, what amount each and what is the final pH. 
    That way we can know what is happening.

    I don’t know if I can tell you the complete list of the ingredients and the amount due to confidentiality but what I can tell you is that for the deodorant with sodium bicarbonate, there is 18% mass percentage of sodium bicarbonate (in mixture with some oils, butters, kaolin, corn starch, zinc oxide) whereas the other deodorant has 17% of magnesium hydroxide, <4% L-arginine and <1% zinc ricinoleate (the remaining ingredients are the same as for the deodorant with sodium bicarbonate - although in slightly different mass percentages).

    Both products have a pH value of 9.

  • MarkBroussard

    Member
    July 16, 2021 at 7:36 pm

    @Minichemist6

    The key to finding the answer to your question is:

    Take a look at the chemical structure of MgOH and Sodium Bicarbonate.  Note that the anions are quite different.  What would happen to those anions in the presence of water (ie: sweat)?

  • Minichemist6

    Member
    July 16, 2021 at 9:19 pm

    @Minichemist6

    The key to finding the answer to your question is:

    Take a look at the chemical structure of MgOH and Sodium Bicarbonate.  Note that the anions are quite different.  What would happen to those anions in the presence of water (ie: sweat)?

    Oh my! Thank you so much for this answer. I’ve been stuck because I’ve been looking at it from a wrong angle. 
    Glad I asked in this forum. I wonder how long it would have taken me to realize that I’ve been approaching it the wrong way ????

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