Print. Email. Lead is definitely harmful for adults to ingest or breathe, a fact known since the second century A.D., when a Greek physician named Dioscorides said, “Lead makes the mind give way.” Of course, the greater the exposure, the more severe the symptoms.rint. Email. Lead is definitely harmful for adults to ingest or breathe, a fact known since the second century A.D., when a Greek physician named Dioscorides said, “Lead makes the mind give way.” Of course, the greater the exposure, the more severe the symptoms.