Is It Okay to Use Silicon Scar Sheets on Old Facial Acne Scar?

Silicone sheets are great for thick scars, but do very little for discolored scars. If your scar is discolored, I would recommend a topical Melaquin PM cream for at least three months. 

You can not harm your skin by using them on your face for acne scars, and they may have some beneficial effect, but it could be very subtle and take a long time to achieve. However, if you can tolerate using them and keep them on as many hours a day as possible, it's worth a try. Be aware, though, that they are mostly helpful in flattening raised scars and will not help smooth out most indented scars.