I have a 1/16" paint crack on the inside edge of my rear bumper underneath the trunk lid. I is inside and not visible, but I am concerned with the paint crack spreading.

Does anyone know if small paint cracks spread overtime?

 

What year is this car?

I think what happens is over time dirt/water/ect get in the crack and get under the paint and start to "flake" the paint. If you are worried about it, you might take some clear coat (brush bottle type) and cover the crack to keep "things" from getting in there....of course clean the area first.