What Is Alum?
Most alums have an astringent and acid taste. They are colourless, odourless, and exist as a white crystalline powder. Alums are generally soluble in hot water, and they can be readily precipitated from aqueous solutions to form large octahedral crystals.
Alums can easily be produced by precipitation from an aqueous solution. In producing potassium alum, for example, aluminum sulfate and potassium sulfate are dissolved in water, and then upon evaporation the alum crystallizes out of the solution.
Usually, when you hear about alum it is in reference to potassium alum, which is the hydrated form of potassium aluminum sulfate and has the chemical formula KAl(SO4)2.
Potassium alum is a fine white powder that you can find sold with kitchen spices or pickling ingredients. It is also sold as a large crystal as a "deodorant rock" for underarm use.
Alum in deodorant may be absorbed through the skin into the bloodstream.
Although it is deemed safe enough for this purpose by the Food and Drug Administration, there may be negative health consequences from continued exposure to aluminum ions in the alum.
Because some of the product is absorbed into the skin, one way to cut your exposure to the product is to apply it every other day, rather than every day.
Alum is the key ingredient used in styptic powder and pencils. The small amount absorbed into the bloodstream from occasional use shouldn't cause health problems.
Alum from natural sources may contain impurities, including toxic metals such as chromium. Because the chemical composition of natural alum is variable, it's best to avoid its use when there is a chance of ingesting the mineral or getting it into the bloodstream.
Uses of Alum
Alum has several household and industrial uses. Potassium alum is used most often, although ammonium alum, ferric alum, and soda alum may be used for many of the same purposes:- purification of drinking water as a chemical flocculant
- in styptic pencil to stop bleeding from minor cuts
- the adjuvant in vaccines ( a chemical that enhances the immune response)
- deodorant "rock"
- pickling agent to help keep pickles crisp
- flame retardant
- the acidic component of some types of baking powder
- an ingredient in some homemade and commercial modeling clay
- an ingredient in some depilatory (hair removal) waxes
- skin whitener
- ingredient in some brands of toothpaste
- Britannica, The Editors of Encyclopaedia. "Alum". Encyclopedia Britannica, 3 Apr. 2014, https://www.britannica.com/science/alum. Accessed 24 May 2021.https://www.britannica.com/science/kieserite
- https://www.thoughtco.com/what-is-alum-608508
- https://www.thoughtco.com/is-alum-safe-to-eat-use-607367