I have had this problem for a long time now and I can't figure it out after doing searches on the internet. Hopefully someone here can identify what this is!

Whenever I scratch my scalp (it's always itchy) I get this thick, waxy stuff under my nails. It looks creamy white, but if I put it on a piece of white paper then it looks a little yellowish.

It doesn't flake off, it seems to greasy for that, so if it is dandruff it would be the oily kind. But it could also be excessive sebum buildup, and I can't figure out the difference between the two. Both leave a cruddy buildup, and both are itchy.

I prefer to CG wash my hair, but I usually can't break through that buildup so it just gets thicker. A few shampooings help clear it up, but then my scalp is even itchier than before and usually pretty irritated by the shampoo. The buildup is dry and what is left will flake a bit, but I still don't know if it is actually dandruff or leftover, dried-up sebum?

Does anyone have any insight into this gross topic? I hate for this to be my first post, how embarassing!, but the outcome will definately impact what method I'll be using to treat my hair. Thanks in advance!