You want a long drawn out answer? Ok then. Simple fact, our world is naturally dirty, just go outside in spring and you'll breathe in untold amount of pollen everyday. Yet our lungs cope. How? By excreting mocus and its cilia to carry out foreign material out. However, if an excess amount of foreign material overwhlems the protections the lungs offers, then problems occurs. That of course ignores materials that are toxic, radioactive, or carcinogenic. So unless you are using a pencil made from pure carbon-14... its harmless.

If you wanted clarification or a ELI5, next time just ask instead of being passive agressive.