Hi, I can understand the concern for little red spots after tattoo on back, spreading. You have not told us your age, sex and occupation so that a close diagnosis could be established This can be simple allergic reaction to tattoo ink. It is quite common to find contact sensitivity due to ink used in tattoo. I advise you to not pinch or pop the area otherwise these areas are very prone for getting secondary infection. For time being period you can apply steroid based cream such as mometasone or cortisone and take antihistamine tablet such as loratadine or cetrizine. Do not try to even touch or pinch the area as can cause more aggravation of the problem. Take care.