I broke my best fingernai/fingerprintl/wrinkle brush, and the other
one has bristles on both sides, one side stiffer than the other.
After a while, it's not comfortable to rake the stiff bristles over my
tender fingers.

But I had this old car washing brush. They probably still sell them.
It's shaped like a rowboat, rounded at the front but coming to a
point. Flat at the back. This one is red with whilte bristles.

I guess it's meant to not scratch the car's paint -- Are you really
allowed to use a brush on the paint? -- but it works well on my
hands, even without soap, getting all the oil etc. of my fingerprintes
and the wrinkles on the top of my knuckles. And it's much bigger
too, so it goes faster. It works even better than the broken
briush did.