Alum is not tasteless. I can tell the difference, sometimes, between a recipe made with better baking powder, and one made with a baking powder that has alum in it. Having said that, the amount used in baking is infinitesimally small. Think about it, you use less than a teaspoon of baking powder in a whole 12-serving cake, and alum is not the sole ingredient. But what you suggest, putting large quantities dissolved in water directly in contact with an orifice is shocking! Don't you think if they were bright enough over a century ago to ban its us as a bread whitener that we ought to be smart enough now to not ingest large quantities of it? Did you know that the skin is so absorbent, that a 15 minutes shower is almost as hydrating as drinking six glasses of water? Just something to consider.