When was the last time you cleaned your make-up brushes? Really? I admit that I can get a bit lazy when it comes to this - and it takes my skin to breakout before I give my brushes a good clean. You should really clean them every 3 weeks or so to keep any nasties away from your face. I am trying my hardest to remember as it shouldn't take a breakout for me to give my tools a good clean - I have been very good over the last 3 or 4 months and keeping on track with it though!
I don't go and buy special brush cleaner as I prefer to use warm water with about a cup of white vinegar and a couple of lemons as they both provide excellent antibacterial properties (plus, it is a lot cheaper this way!). Allow the brushes to soak in the water and vinegar with the lemons halved and in the bowl too, then after a few minutes take each brush in turn and swirl and scrub them with the lemon (the flesh in the fruit acts as a natural brush and helps remove any residue from the brushes). Rinse them well under a warm tap and then allow to fully air dry before using them again.
Easy, isn't it? And you probably have white vinegar and lemons lurking in your kitchen so why not give those brushes a good scrub?