In most patients, after treatment of blackheads, their black tissue is destroyed and a gap or space is formed locally, i.e. a hole is formed. Most patients can basically achieve flattening through natural repair. However, if the blackhead is deeper and wider, temporarily beyond repair and cannot be repaired by itself in the short term, grinding can be adopted for multiple times to promote the repair of small defects with better results. In addition, acne and scars can be re-grown by sanding techniques to make the depressed tissues grow again so as to avoid leaving acne marks, pits and other after-effects.