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What is the amount of baking soda that would be considered toxic for skin? I ask because there is a lot of misinformation online about using baking soda as a "natural" underarm deodorant, and how it is or is not harmful to use as such. Please clarify.

Thank you for your time in advance.

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  • $\begingroup$ I wouldn't recommend labelling it "misinformation" until you actually know it to be false. $\endgroup$
    – SendersReagent
    Mar 25, 2016 at 19:34
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    $\begingroup$ Here is a material safety data sheet (MSDS) for sodium bicarbonate. sciencelab.com/msds.php?msdsId=9927258 It is about as harmless as a chemical can be. // I'm unsure about how it would be used as a deodorant. The grain size of typical grocery store purchased baking soda would be abrasive to the skin. // I don't know if you're reacting to the fact that baking soda is a "chemical" or not. Water is a chemical, and oxygen in the air is a chemical. It is true that a strawberry isn't "a" chemical, it is made up of thousands of chemicals. $\endgroup$
    – MaxW
    Mar 25, 2016 at 20:15
  • $\begingroup$ I used soda bicarbonate as an underarm deodorant for about three years. Not every day but fairly consistently. At a certain stage I noticed aching shoulders, and I stopped it's use. I used a brand that had "aluminium free" printed on the label, which suggests some producers mix aluminium into their soda bicarbonate. Poor soda bicarbonate can't fight in the heavy-weight ring without some additives. When we talk about soda bicarbonate, what other additives are we talking about and blaming on sweet little soda. Without a full spectrum microscope what do I know? $\endgroup$
    – Alan Keating
    Jun 3, 2017 at 16:43

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Baking soda is sodium hydrogencarbonate, $\ce{NaHCO3}$, also known as sodium bicarbonate.

The only toxicological data in the GESTIS database on hazardous substances is a LD50 of 4220 mg/kg for the oral uptake by rats. There are no data for dermal uptake.

In water, $\ce{NaHCO3}$ is weakly alkaline. I do not know whether it might cause skin irritations, particularly in more sensitive regions, such as armpits.

In occupational safety, I'd recommend to avoid skin contact and use personal protection equipment when handling it.

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    $\begingroup$ I'll expand Klaus's answer a bit. By "occupational safety" he means like if you're working in a plant where sodium bicarbonate is being made. In that situation there would likely be a significant amount of sodium bicarbonate dust floating around. // Taking 1/2 teaspoon from a box to make a cake in a kitchen is safe under ordinary use, and doesn't require any more care than handling salt, sugar or cocoa powder. $\endgroup$
    – MaxW
    Mar 25, 2016 at 20:25
  • $\begingroup$ Baking soda is used in many kitchens for baking purposes. Do you bake anything? If so do you always wear PPE? Occupational safety people often recommend wearing PPE for everything all the time no matter what, perhaps because their primary concern isn't the safety or convenience of the people they oversee, it is protecting the liability of the firms they work for in the case of lawsuits. $\endgroup$
    – Curt F.
    Mar 25, 2016 at 20:39
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    $\begingroup$ @CurtF. Yes, I do cook and bake - without gloves or a mask ;-) Nevertheless, occupational dermatitis is among the top list of work-related health problems. I agree that occupational safety people who "recommend PPE for everthing all the time" do a lousy job! PPE is the last resort, when other measures (substitution, technical measures, etc.) can not be applied. $\endgroup$
    – Klaus-Dieter Warzecha
    Mar 25, 2016 at 21:06
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    $\begingroup$ @CurtF - I agree with you to a point. I worked for IBM in a chemical environment making chips. I remember commercials on TV showing a lady with makeup and a dress cleaning an oven with spray lye cleaners. She at least did have rubber gloves. On the IBM production line you'd been in a full hastmat suit to do such a thing. But lawsuits are a powerful motivator. So here is a case of the golden rule. Him with the gold makes the rules. So if you wanted to work on the IBM production line, you followed IBM's safety rules. The rules protected both IBM and the workers. $\endgroup$
    – MaxW
    Mar 26, 2016 at 6:39

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