I have a habit of eating graphite pencil leads since 1 year.i just open the wooden coating of pencil with my mouth and eat the lead inside it.by eating pencil leads,is there any problem in future like cancer?

The "lead" of pencils is an inert material called graphite. You poop it out in your stool like other indigestible debris. I know of no studies that looked at the long term ingestion of this material nor would I expect them to be done in the near future. Eat at your own risk.

Pencil lead is actually a mixture of graphite and clay, which is dried. It is relatively non-harmful and will not cause cancer. good luck.