Allergic reaction to Oxy5 acne medicine on acne blemish left a 8mm round indented scar on my cheek. Had collagen injection under the cheek scar an another one indented scratch scar on my forehead. Turned out to be allergic to collagen as whenever I went in the sun for almost two years later the treated area would swell.
A few months after the injection I met a permanent cosmetics professional who needled the scars. You could hear the fibers pop during the treatment and the scars filled with blood but really didn't bleed. Over the next few days I kept squeezing around the treated areas so they didn't collapse downward again. The scars are still there but they are level with the rest of the skin. One of the best things I ever did!