Many e-commerce sites sell alum, including Amazon.com, Walmart.com, and eBay.com. Depending on its intended application, alum sold on these websites can be found in the food, crafts or personal care category.
Potassium alum, which is the most common form of alum, is usually sold in powdered form. It is often used for canning, as baking powder and as an ingredient in aftershave to stop bleeding from minor cuts. It can also be sold in crystal form; in this form, people use it under their arms as a deodorant.
Alum is approved as a food additive by the U.S. Food and Drug Administration, but it can be toxic in large doses. Long-term exposure to alum should be avoided.