What Causes Pus Filled Blisters On The Chest And Armpit?

my girlfriend has these large pimple like bumps forming on hr underarms and chest. they are about 5 - 15mm and stay around for months if not years. when popped they produce LARGE amounts of thick white/yellow puss and small white hairs. some even smell really bad. they never dissapear and she has had ones about 10cm in diameter which pussed profusly for 2-3 days. any ideas????