Combine a teaspoon of soap with 1/4 cup of water in a small bowl (warm water works best)
Swirl the brush tip in the soap while pressing on the sides of the bowl until the makeup debris comes off, then rinse under cool water.
Repeat step 2 until the water runs clear.
Pat dry bristles, making sure they still keep their shape and place them on a towel to dry.
In my experience, leaving makeup brushes to dry for at least 12 hours is worthwhile (have you ever tried applying makeup with a wet brush? It’s grim!)
Notes
In my experience, leaving makeup brushes to dry for at least 12 hours is worthwhile (have you ever tried applying makeup with a wet brush? Gross!).
It's important to keep the bases of your makeup brushes out of the water when cleaning. Dip the bristles in the water, avoiding the handle and base.
Try, if you can, to get into a habit of cleaning makeup brushes once a week. This will really help your brushes last that much longer and prevent your skin from being irritated by crusty makeup debris.
This is a one-time use cleaning solution - so once you’ve cleaned your brushes, throw it out.