My answer: I clean it once a week. I tend to use a new brush every time when the used brush is dirty. That's why I have so many make up brushes at home =.=". I will just wait until all brushes of mine are dirty lol. I'm just way too lazy to clean them after usage. So yes... I'm guilty for not cleaning it on a regular basis =(.
It's not hygienic to use the same brush for the whole week or even longer than a week girls. Bacterias will go in and stay on the make up brush and this can cause pimples or acne! So make sure to clean your brushes more often ;)!!
But tell me girls... how often do you clean your make up brushes?