Bacteria can build up so easily, so its good to wash your brushes at least once a week. You can do this with a baby shampoo – nothing too harsh. Wash and gently squeeze out excess water. Lay flat on towel to air dry.
I normally use a makeup remover spray after using my brushes each time and giving them a deep clean once a week.
Remember dirty brushes can cause breakouts plus the build up won’t allow the brush to distribute powders properly.