MadSci Network: Biochemistry

Re: Is potassium alum - KAI(SO4)2 a negatively or positively charged ion?

Date: Thu Dec 27 13:25:00 2007
Posted By: Eli Hestermann, Assistant Professor
Area of science: Biochemistry
ID: 1195598369.Bc


I know this isn't related to your question, but first I want to address the concern that aluminum exposure may be related to the development of Alzheimer's Disease. The easy answer here is that the results are inconclusive, which gives hope to both sides of the debate. A better scientific response, though, is that so far there is little evidence to suggest a connection, and in fact the Nation al Institutes of Health advises seniors that no connection exists. (Incidentally, the NIH also find no conclusive link between deodorants and breast cancer. I'm sure you were sweating [ha ha] that one too.)

With out-of-date information still circulating, though, and given the difficulty of proving a negative such as "aluminum in deodorant is definitely not linked to Alzheimer's," some people are concerned about the possibility of being exposed to aluminum. In order to investigate this possibility, researchers at Penn State and Purdue labeled the aluminum in aluminum chlorohydrate (the common active ingredient in antiperspirants) and then monitored levels of the labeled aluminum in blood and urine following application under the arms. They determined that only 0.012% of the aluminum was absorbed, which amounts to about 2.5% of the amount people absorb from their food.

Although no direct studies have been conducted, I doubt absorption of aluminum from potassium alum is any higher. Therefore, in one respect, the marketing you saw is probably true: the aluminum ion is not absorbed. However, since it's not really absorbed from typical antiperspirants either it's hard to see how this is a benefit.

There is one big difference in how aluminum chlorohydrate and potassium alum work. The former causes swelling of cells that line sweat ducts, squeezing them closed and reducing the amount of sweat. These are effectively "antiperspirants." Alum, on the other hand, is not an antiperspirant, but instead appears to slow the growth of bacteria that produce the odor.

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