How many microns deep does laser resurfacing need to be to cause scarring?

Scarring can happen even after very low energy low density procedures. Scarring often has to do with your own bodys response to the laser/energy.  Although, it can often be a result of too strong or inadequate technique.  The energies you are describing are very low.  I suggest you speak to your physician.  The current treatments you are trying are some of the best options. Dr. Emer.

Sorry to hear of the poor results you have experienced with laser skin resurfacing. Your doctor seems to be managing the problem appropriately. Due to a variety of factors including multiple laser devices used, it is not easy to answer your question about depth of ablation. Good luck with your healing.

From the information you posted you had both erbium and CO2 laser done to the area.  The effects of both lasers are cumulative and the injury to the skin would be deeper than either laser done alone.  It's not possible for me to say how deep the injury was in microns but clearly you had a dermal injury.  I'm sorry to hear about your side effects and I wish you a speedy recovery.Regards,Dr. Ort