The back of your neck is sensitive, and you should avoid shoving a brush in there. You can use a loofah or washcloth to scrub the back of your neck gently. If this doesn't work, you could try using some Exfoliating Gel to help remove dead skin cells and dirt from your skin, which will help clear up those nasty whiteheads, blackheads, and pimples on the back of your neck.