Certain types of mold are bad for us. It is bad if we breath too much mold in general. (Notice in this experiment, he keeps the bag closed so that he does not breathe in any of the mold spores. You should not complete this experiment without putting proper safety measures in place.) Is mold always bad for us? A. Yes, it is always bad for us. B. No, it can be good because it can make penicillin and soy sauce.