Sounds like seborrhoeic dermatitis to me. We've got a number of members who deal with it.
What works varies from person to person, but I think a lot of people get some relief from rinsing with diluted vinegar. I think I've also read that people have had good results using shampoo bars, but that generally requires vinegar rinses too.
ETA, rather late...
As others have said below, some sebum is totally normal, and to have an absence of any oily white-to-yellowish gunk under your fingernails after a day or two of not washing would be a bit unusual and would probably contribute to having dry hair. SD occurs when you have unusual amounts of it, irritation/itching, and perhaps some bug/fungus/whatever that's proliferating in the excessive sebum. Lots of the SD pictures look really nasty. Also look up "cradle cap" -- it's the same thing essentially, but tends to be the name in babies and small children.
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