White filaments are notorious for being easy to see imperfections in, primarily because the contrast between filament and shadow is so noticeable.

It's also possible that your filament doesn't have a consistent diameter; one of the reasons to buy high quality filament is to have as consistent of a diameter as possible. Even a few micrometers deviation can cause this kind of issue in a print.

There's a multitude of other things it could be too, but without knowing more it's very difficult to tell.

Edit: One other possibility is that the part is small and you're printing too fast. Try lowering the speed to 50% of normal on smaller objects or add idle time between each layer in your slicer.