Okay, so just when you've mastered knowing which make-up brush is for contouring and which one creates the perfect smokey eye - you find out you gotta keep them clean!?
Okay, this shouldn't really come as a big shock, but yes - your brushes should be kept clean, and giving them a good wash every 2 weeks (at least) or anytime you switch a product will keep them in best possible condition and make them last twice as long!
