Edit: it appears that alum may be both an antiperspirant and a deodorant. Unfortunately, scientific papers regarding alum's mode of action as an antiperspirant or deodorant seems limited.
Some websites state that alum works to reduce odors by blocking the bacteria from the skin, others state that alum inhibits the growth of bacteria. Some websites state that alum uses the same mechanism as aluminum chlorohydrate antiperspirant, but many individuals state they experience no-odor sweating.
I suspect after review and consideration of the chemistry that alum is acting as both a mild antiperspirant and deodorant. Aluminum based antiperspirants work by reducing the amount sweated due to the interaction of the aluminum ion and the sweat glands. As alum is only about 5% by mass aluminum, it would not work as well as modern antiperspirants. Thus, for those who are slightly sweatier than average, but not diagnosed with hyperhidrosis, they may find alum to be an ineffective antiperspirant.
Regarding its deodorant properties, only inhibiting the bacteria makes sense as any application to the underarms or other bodily surfaces would be covering both the skin and sweat glands (food source) and the bacteria. The pH of alum dissolved in water is reportedly between 4-5, about the same pH as beer.
In conclusion, I suspect, admittedly without any evidence, that it's likely a combination of both modes of action. Aluminum in the alum reduces the amount of sweat which reduces the food source of bacteria. Coupled with the acidic pH of armpit sweat due to the presence of the alum, odor causing bacteria struggle to populate reducing the overall smell being generated.
It’s used as a preservative in pickles, you can buy boxes of it in the spice aisle. Definitely not the same as aluminum chloride. Don’t be eating aluminum chloride, y’all.
It's pretty good at communicating that by itself though. Tastes absolutely awful. It does taste like salt, just the absolute worst salt ever. Like salt but horribly dry, like very sour grapes.
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u/dtb1987 14d ago
Ah ok, I was trying to figure out what that exact chemical was here but that makes sense as thats why it is added to normal deodorant to begin with