White stuff in hair? It's not dandruff...?

Hey guys :) I'm a 15 year old female with long hair (almost to my bellybutton) and its not thin or thick. Just normal. Anyways, whenever I scratch my head I get this white creamy stuff under my nails, and I know its not dandruff or lice. I dunno why I keep on getting this though, I wash and condition my hair everyday. My hair is slightly on the dry side, though. How can I get rid of this?!