Is it common in people eating pencil leads? are there any cancer causing things in lead pencils? i have an habit of eating pencil leads and chewing wooden pencils?

Compulsive chewing and ingestion of non-food materials is called pica (google it for more info). Pencil chewing is a common form. This particular ingestion is not likely to be harmful, if not in very large amounts. Other commonly ingested materials can be medically harmful and pica also can be associated with serious psychological conditions. Discuss this with your doctor. Good luck.