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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
    Commented May 2, 2021 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
    Commented May 2, 2021 at 19:11
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    $\begingroup$ 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
    Commented May 2, 2021 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
    Commented May 2, 2021 at 20:23
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    $\begingroup$ 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
    Commented May 4, 2021 at 0:50
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    $\begingroup$ 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
    Commented Jun 10, 2021 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
    Commented May 2, 2021 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
    Commented May 2, 2021 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) $\endgroup$ Commented May 2, 2021 at 23:08
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    $\begingroup$ 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! $\endgroup$ Commented May 2, 2021 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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    $\begingroup$ 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. $\endgroup$ Commented Jul 13, 2014 at 20:48
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    $\begingroup$ Tried it, to no avail, sadly! Tried just the soda and soda with vinegar $\endgroup$
    – Tony Sepia
    Commented May 3, 2021 at 10:26
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I have been looking for a solution to two related problems:

  • yellow armpit stains on white cotton t-shirts
  • antiperspirant gunk buildup on polyester gym t-shirts.

Oxiclean 24hour soak helps with light yellow staining on white t-shirts but does nothing to dissolve antiperspirant buildup. Oxiclean is a mix of washing soda and some sodium percarbonate. Didn't have any luck with pure sodium percarbonate.

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I’ve had rather good luck using OxiClean powder to get out those types of stains.

I’m not 100% sure about the chemistry, however the procedure that I follow does appear to result in some sort of exothermic reaction. It’s likely an oxidation reaction with the Aluminum that’s in that polymerized Aluminum compound.

Here’s what I’ve found works:

  1. Turn all affected garments inside out. The stains are mostly on the inner surface, as the source was antiperspirant near the armpit area.
  2. Follow the usual instructions for an OxiClean soak: Fill to line “B” on the scoop, one scoop per gallon of water.
  3. Soak for 1-6 hours (I usually do 1hr, as I’ve found that soaking for longer does not help much on its own)
  4. Put on gloves. I use nitrile gloves, but any waterproof and chemical resistant gloves for direct contact with the sodium percarbonate (OxiClean).
  5. For each piece of laundry:
  • a. Pour a small bit of OxiClean powder directly on the garment’s armpit area
  • b. Make sure the powder is only slightly wetted, you want a nice paste to form. I use warm or hot water to wet the OxiClean powder.
  • c. With gloved hands, grab two adjacent parts of the fabric near the garment’s armpit area
  • d. Rub the fabric together, kneading in the OxiClean paste and powder bits into the fabric.
  • e. If you’re doing it right, and the garment has enough Aluminum compound stains, then you will feel the fabric begin to heat up.
  • f. Once the heating effect disappears, then start dunking (scoop some water on top of the armpit area fabric) and rinsing the fabric.
  • g. Work the fabric’s weave back and forth with each hand gripping the fabric between thumb and forefingers. You want to try and work the woven netting back and forth by gripping two pieces between fingers on each hand, then moving each hand in opposite direction from the other, alternating directions back and forth. This opens up the weave and lets the water wash some of the polymerized gunk out as you keep dunking and rinsing.
  1. Repeat step 4 (a) through (g) for each affected armpit area on every garment.
  2. Run the garments through the laundry, and make sure the extra rinse option is turned on if your laundry machine has one.
  3. Check the results after the rinse and spin cycle is completed.
  4. If some garments still have polymerized gunk in the armpit fabric, then repeat steps 4 (a)-(g) through 7 until you’re happy with the result.

I notice after step 4.f that usually there is some slightly waxy white substance that has adhered to the clumps of OxiClean powder. The mechanical rubbing action seems to be important to get those polymeric compounds to bead up and roll out of the fabric. The OxiClean powder itself also helps to add some friction for helpful scrubbing action. Meanwhile the chemistry involving the sodium percarbonate reacting with the Aluminum and Aluminum Oxides seems to help the polymers break up and lift out easier. Since most chemical reactions are dependent on concentration, the use of bare OxiClean powder with small amounts of water appears to help by forming a localized super-concentrated mixture of water and Na₂H₃CO₆. The extra heat generated either by the reaction with Aluminum or simply the water hydrolyzing the OxiClean powder also helps localize a self-generated heat source directly on the stain, helping any other reactions take place.

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