You're conflating two things, so just to be clear about both bad things, for everyone else: Alpha radiation is massively damaging, but is blocked entirely by t

You're conflating two things, so just to be clear about both bad things, for everyone else: Alpha radiation is massively damaging, but is blocked entirely by the outer, dead layers of skin. Once it gets inside your body where it can access vulnerable tissue, it's a different story. Contamination (think "source of radiation") that gets inhaled or ingested (committed) is bad because you fractionally take it with you, getting continually irradiated. Even worse, some committed contamination eagerly accumulates or replaces in processes where it won't be exchanged out. This is the case with iodine, and that is why iodine pills can be helpful in large releases of radioactivity.