Subject: Is a potassium alum molecule too big to be absorbed into the (human) skin?

Too many inconsistent answers.  

1) Some claim that potassium alum, when applied to the skin via a solution of
water etc, releases the exact same Al3+ ions, which is aluminum and so by
dissociating in water it still delivers aluminum in the system.      

2) It is said that some deodorant stones (or
solutions) feature physically large potassium or ammonium alum molecules and are
not absorbed into the skin/blood. Water has a molecular weight of 18. A
potassium alum crystal molecule has a molecular weight of 474.38. A potassium or
ammonium alum crystal molecule, in solution, is hydrated 24 times and
consequently has a molecular weight of 654. It is impossible through natural
means to get water to permeate the skin. Witness the large number of
moisturizers available at the cosmetic counter and imagine how difficult it
would be for a molecule that weighs 36.3 times as much as water to permeate the
skin.  

I would like to find out which is accurate.  Thank you.  :)  

Re: Is a potassium alum molecule too big to be absorbed into the (human) skin?