This is a major drawback with mesh sculpting, weight painting and mesh hiding. No brushes work on back faces. This makes an extremely difficult case of working with hair particularly (where a lot of back faces are facing the front), and many other like with weight painting where dense mesh is sometimes get completely deformed with movements and you need to straighten it up. But a lot of faces are twisted and it is practically impossible to use a weight brush to fix it. You have to export and use third party tools to rectify.
Please made brushes to work on both sides of the mesh and create an option (a check box) to work only with front faces.