If you don't wash your makeup brushes, you are doing your skin a disservice. Dirty makeup brushes can lead to breakouts! I always clean my brushes once a week, it's simple and only takes a few seconds. Every week I spray my brushes with Sephora Daily Brush Cleaner to the point where they are wet and lay them on a clean paper towel to dry. I especially love this one because it's a spray bottle, so it's easy to use and it's antibacterial. Since I don't wear heavy makeup on a daily basis, I really don't need to clean my brushes daily - weekly does the trick.
About every other week I use baby shampoo to thoroughly wash all my brushes. I get warm soapy water and dip the brush head in the water and swirl it around. After I finish that I allow the brushes to dry on a paper towel. Simple and easy. Don't want to wash your makeup brushes? Use your fingers to apply your makeup!