Facelift 1 month ago. Chin incision doing well. Big hard crusty leaky scabs formed behind ears. Why did this happen? (Photo)

You have had some skin die off behind the ears.  This can occur due to the tension on the wound - the skin is too stretched - and the blood flow is not adequate to keep it all alive.  The skin will turn dark and then fall off leaving you with a scab.  The scab will often start out dark, and then become yellow and moist as it heals.  You should keep it moist with antibiotic ointment.  It will heal, and often you can't see any residual scar.  If you do get scarring there are lasers that can be  used to improve the scars.     

is likely to have caused this. The scab is at the margin of the incision and likely to represent necrosis of the flap periphery. Keep it clean and use bactoban, bacitracin or fucidin ointment. It will heal and may not be noticable. It is possible however that the scar may need resurfacing should it be problematic. This is a simple local anaesthetic procedure. Your PS will have a preferred laser. I would use fractional CO2.

The area behind the ear of the facelift is commonly understood tension and has relatively poor blood supply. Difficulty healing is not uncommon. Fortunately most the time the results are quite good with just good care of the one. I only assist the patient's keep the skin clean and covered with a good emollient.