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I have recently found out that the white/yellowish "sweat" stains one occasionally finds on t-shirts might be aluminium chlorohydrate polymers.

While talk about aluminium and antiperspirants is all over the press and there are lots of DYI-instructions for removing them, they all sound quite pseudoscientific. I find it strange, for instance, that some guides recommend both vinegar and/or baking soda as a remedy...

Any ideas what else I could use to dissolve such stains without also dissolving much of the pigments?

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  • $\begingroup$ I am surprised that there still hasn't been a single chemistry-based answer to this! I've started a bounty to attract more attention to this question $\endgroup$
    – Tony Sepia
    May 2 at 12:43
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Bleach and baking soda are no use for removing deposits of aluminum chlorohydrates. These deposits are made of $\ce{Al(OH)_{𝑥}Cl_{(3−𝑥)}}$ and they are only soluble in somewhat concentrated $\ce{HCl}$ or $\ce{NaOH}$ solutions, whose pH are either $<1$ or $>13$. $\ce{HCl}$ solutions are not always available in domestic settings. $\ce{NaOH}$ solutions are available in specialized stores selling strong liquids for cleaning oven windows darkened by soot. This liquid is a rather concentrated solution of $\ce{NaOH}$. It should be diluted at least $10$ times with water before using it on a T-shirt. If not, it could hydrolyze your T-shirt. And take care ! It is corrosive for the skin. Use gloves ! It may also change the color of the T-shirt.

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  • $\begingroup$ Thank you! In 17 hours I will be able to award the bounty; I've set an alert to do so. Your precise answer is greatly appreciated! $\endgroup$
    – Tony Sepia
    May 2 at 19:11
  • $\begingroup$ to be precise with dilution: should I look at getting a 10% solution of NaOH, or do I need less than that for the purpose of treating fabric? $\endgroup$
    – Tony Sepia
    May 2 at 19:19
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    $\begingroup$ The concentrated solution I was mentioning is probably $50$% $\ce{NaOH}$. A 10% dilution is about $5$% in$$\ce{ NaOH)$.. if you use it for destroying aluminum chlorohydrate deposits, do it quickly. The dissolution should be done in a couple of seconds. Rinse without delay. $\endgroup$
    – Maurice
    May 2 at 20:23
  • $\begingroup$ I would assume however, that an $\ce{NaOH}$ solution at $\ce{pH\geq13}$ would not really be fabric or pigment-friendly. Are there any alternatives, and if I have the means, could I expect better results from $\ce{HCl}$? In personal anecdotal experience from chemistry courses strong non-oxy acids took a lot longer to burn into my skin and clothes than strong bases. $\endgroup$
    – TheChymera
    May 4 at 0:50
  • $\begingroup$ I can confirm that this works. Used on a black t-shirt (with several years worth of aluminium!) precisely as instructed above, and had great results - fabric and colouring were not damaged. $\endgroup$
    – Tony Sepia
    Jun 10 at 11:22
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My undershirts have turned yellow in the armpit area without the benefit of aluminum antiperspirants. I assumed the stains were from carbonaceous exudants from my pores - or the biogenic products of bacterial life on my skin.

So I bleached the undershirts, soaked them in a diluted bleach (sodium hypochlorite) solution (about 1 in 10, I think). BIG improvement. Not perfect, but very good. One of the side effects was that the undershirts turned blue in the bleach because of the whiteners in the surfactant used to wash them. But that faded as the bleach continued to oxidize the stains.

You can go overboard and use more concentrated bleach: this will perk up the entire undershirt! Interestingly, it seemed to not only clean the underarm stains, but also attack/weaken the fabric there, so the stains went away, but small holes started to appear there, which grew larger and larger until the undershirts became nice dust cloths.

Next time, I think I will try an oxygen laundry bleach, even if it takes longer. Or H2O2.

Addendum: the supposition that the brown deposits in the armpit area are due to aluminum compounds is widespread. Even undershirt makers suggest it - but of course, take no blame for providing the substrate that shows the stain. One manufacturer (https://thompsontee.com/blog/the-science-behind-your-pit-stains-and-what-to-do-about-it/) even has a link to fixing it. What do they suggest? Change your antiperspirant; take proper care of your clothing; wear a sweatproof undershirt. (They offer the best sweatproof undershirt: 20% off!) But how to get rid of armpit stains?

#1. Vinegar, baking soda and HYDROGEN PEROXIDE.

#2. OxiClean or Raise Stain Remover (mixed reviews)

Nivea makes deodorants and has a site that recommends ways to remove armpit stains: try an acid. For example: #1: HYDROGEN PEROXIDE #2. Baking soda (?) #3.White vinegar #4.Lemon juice. https://www.nivea.com.au/advice/skin/removing-deodorant-sweat-stains

The desire to use environmentally safe washing agents in certainly admirable, but when you have to do a job, it is quicker to use the powerful tool. Of course, there is a learning curve. I love bleach because its activity is so adjustable and controllable - from an additive at low concentration to eradicate gingivitis by waterpicking to clothes cleaning to mildew removal from house siding, and probably a million more uses.

But I suppose hydrogen peroxide will be adequate. Or OxiClean.

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    $\begingroup$ Bleach and baking soda are no use for removing deposits of aluminum chlorohydrates. These deposits are made of $\ce{Al(OH)_xCl_{3-x}}$, and they are only soluble in somewhat concentrated $\ce{HCl}$ or $\ce{NaOH}$ solutions, whose pH are either <$1$, or > $13$. $\endgroup$
    – Maurice
    May 2 at 14:53
  • $\begingroup$ Hi @Maurice, I think your comment is very close to the answer I was looking for! If you post it as an answer and perhaps suggest how one could access the solutions in domestic settings I would like to award the bounty! $\endgroup$
    – Tony Sepia
    May 2 at 18:11
  • $\begingroup$ @Maurice: Aluminium chlorohydrate is a group of water-soluble,[1] specific aluminum salts having the general formula AlnCl(3n-m)(OH)m. (Wikipedia) $\endgroup$ May 2 at 23:08
  • $\begingroup$ I was telling my wife about this issue at dinner tonight. She said, "Have they tried Spray and Wash?" She does have a chemistry degree, but even more valuable, she does laundry! $\endgroup$ May 2 at 23:10
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Have you tried baking soda or washing soda? It may sound pseudoscientific but many people have had success.

Even more successful is using baking soda as a deodorant, avoiding the aluminum altogether.

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  • $\begingroup$ I might try it if I don't get any more compelling ideas till the next time I do laundry. As for it "working" for many - I would not rely on their objective evaluation. And baking soda as a deodorant? I'd be tempted to ask why then nobody markets it as such. I do try to buy doedorants without aluminium chlorohydrate, but since there are so few brands (that cater to people who want to not perspire, not to go-natural fanatics) which sell them I would guess it's a rather essential compound. $\endgroup$
    – TheChymera
    Jul 13 '14 at 5:21
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    $\begingroup$ Baking soda is dirt cheap so there's no money to be made from it. Baking soda is a base and the malodorous compounds in sweat tend to be acids so the baking soda deprotonates them, making them less volatile and unable to reach the nose. $\endgroup$ Jul 13 '14 at 20:48
  • $\begingroup$ Tried it, to no avail, sadly! Tried just the soda and soda with vinegar $\endgroup$
    – Tony Sepia
    May 3 at 10:26

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