are you using mac's brush cleanser? if not, that may be your problem. it has conditioning agents in it to help prevent shedding. plus, you don't need to rinse your brushes all that often if you use brush cleanser. you only need to rinse them every couple of months or so, if that, to do a deep cleansing. and when you do rinse them, rinse them hair end down, gently squeeze out excess water, and dry flat with hairs hanging over the edge of the counter. let dry completely, about 24 hours or so, before standing them up again.