I tried explaining this to my grandfather, who was a big proponent of said bracelets... I never got through to him. The best "unscientific" blip I've seen on these was someone placing a paperclip against the bracelet and it holds. Then a couple of sheets of paper were placed between the bracelet and the paper clip... the clip fell right off. The magnetic field was so weak when distanced from the bracelet by only a few sheets of paper, it was pretty strong unscientific proof that no field of any significant strength would likely penetrate even the epidermis, let alone into the major bloodstream. Given the distance squared dropoff of magnetic field strength, well... you make the call.
But people want to believe...