Do you only use shampoo, and what kind? You should really use a mild shampoo and then a high quality conditioner. My hair used to be incredibly oily all the time when I used shampoo or shampoo+conditioner combo, even if I showered every day. Now it takes around 3 days to get greasy and I shower every few days. My skin is much more balanced and healthier (less acne, more even sheen, no dryness issues). I also do the equivalent of conditioner for my body- I use cetaphil on any part that I notice routinely gets dry (the bottoms of my feet, elbows, face, knees, etc.) since I started doing all this, my elbows went from being dry and ashy and scaly to looking just like the rest of my skin. I do use deodorant every day and have a bidet, but I don’t have any scent issues as far as I’m aware (I do ask others to check me, and days where I don’t use deodorant, I can smell myself, so I don’t think it’s a false bias.)

So does mine, and my skin too. My ancestry is half Scots-Irish Borderer and a quarter each Austrian and Italian, of which the latter seems strongly expressed in my integument; for example, despite half my family being very fair, my skin has an olive undertone, and I tan easily and well.

More to the immediate point, I likewise have rather oily skin and hair, to the point where if I don't shower daily with ample soap and shampoo, I start leaving smears on anything I touch. I've tried the experiment of going without soap a few days, to see if the oiliness was in compensation, and it wasn't; it's just that I either wash daily or turn into a greaseball, and always have done.

(I'm also one of those people whose skin oil gradually dissolves ABS plastic with regular contact. Of the last ABS set I used, to the tune of ~10M keystrokes, before switching to PBT caps, the spacebar had enough material removed to put a distinct curve in its lower edge where my thumbs would strike. Too, I now belatedly wish I'd put a protector on the Wacom tablet that doubles as a touchpad for my work machine. Not sure if the plastic-melting thing is related, but it seems fairly uncommon and so worth mention in this context.)

I’m a mix (maternal grandfather was Lebanese/Greek, rest of my family various European) and also had fairly oily hair. It also didn’t get less oily overnight when I started washing less, it took maybe a few months and yeah it felt gross. For what it’s worth.