New brushes should be conditioned before the first use to avoid bristles.
Wet the brush, and swirl the brush in BB Frösch Brush Conditioning Soap. Rinse the brush, pulling the lather out until the water runs clear. Beat the bristled end of the brush against the edge of a counter or sink to loosen wayward bristles.
If a bristle does find it’s way onto your painted surface allow your paint to dry first, then try simply rubbing the bristle with your finger or a small piece of 400-grit sandpaper. The bristle should come off nicely without leaving a mark.