Is eating crayons harmful

An abnormal craving to eat substances which are not normally consumed by humans is called Pica. Chalk is not harmful in the sense that it can poison you. Because of it's consistency, however residue is easily ingested into the lungs and could possibly cause pulmonary distress. A person who finds themselves wanting to ingest such things as chalk, talcum powder, etc. is suffering from a mineral deficiency. They should have a complete medical evaluation.