It is very important that you rinse the brush well. If you don't rinse them well you can leave behind soap residue and traces of makeup, not to mention bacteria. Begin by rinsing the brush under cold water, while gently massaging the bristles with your fingertips. Do not pull on the hairs and make sure you rinse from base to tip. Continue rinsing with cold water until all traces of soap are gone and the water runs clean.