There are a few things you can do to clean a boar bristle hair brush. The first is to dry the brush by putting it in the oven on low heat for about 10 minutes. This will remove any excess water and make the bristles more durable. The next step is to clean the bristles by rubbing them with a cloth or a piece of paper. Be sure to use enough pressure and avoid using too much soap or water because this will damage the bristles. Finally, you can put the brush in a dishwasher if it is not already in there.