I assume you avoid aluminium compounds because of possible links to brain diseases correct?
Well alum is an inorganic compound - a rock - like salt.
The possible problematic compounds are organic compounds, so Al-carbohydrate bonds.
Inorganics are mostly water soluble, and often highly stable (like in this case or sodium chloride - table salt) - organics (or in this case more accurately organometallics) are mostly oil/solvent soluble and in this case highly unstable and highly reactive.
I don't know how good you are in chemistry - but it's like comparing something like Magnesium Chloride (sold for it's healing properties as a bath salt) and MethylMagnesiumChloride (CH3MgCl) a highly reactive and acidic compound of which a couple of drops will burn a nice hole in your arm. If you check the formula there is a C-Mg (Carbon - Magnesium) bond and the carbon has further bonds to 3 Hydrogens. This is a so called hydrocarbon and the main component of organic chemistry.
I wanted to compare sodium chloride (NaCl) with a sodium organometallic - but these are so reactive and unstable, that I would have to talk about SodiumCyclopentadiene....
It is a bit hard to explain these things (ask my wife) - but the basic message is the paragraph in red.
Hope I could somehow explain...