What is ammonium alum?

Ammonium alum, also known as ammonium aluminium sulfate, is an inorganic salt used in many over-the-counter products, including deodorants and aftershave. It is non-toxic and very cheap to produce.

The compound sees the most use in the health industry, but is also used elsewhere. For example, it can be found in grocery stores, where it is sold for uses in baking and pickling. It can also be used for making dyes and tanning leather. Alum has flame-retardant traits and is used to fireproof textiles as well as being used as a flocculant in water purification. Finally, it is a main ingredient in vegetable glues and even sees use as an animal repellent.