Makeup brushes (and other applicators) should be cleaned often and this is to avoid a long list of infection!
Just like ensuring a great sense of hygiene with overall health, cleaning makeup brushes should be a habit if you intend to keep skin infections, breakouts, acne, eczema and so on at bay.
It also helps to make them last longer.
Makeup brushes should be cleaned often as leaving them riddled with dirts can cause blemishes and even more serious breakouts on the skin as dirty makeup brushes are breeding places for bacteria.
Cleaning your makeup brushes (see how to here) should however be done carefully, avoiding these listed things:
1. Never soak your brushes in water. Instead run them under lukewarm water to get out the dirt and grimes from foundation, powder, eyeshadow etc