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.     

I'm sorry to hear about your scabs after your face lift.  As difficult as it may be to realize, I'll bet that your scabs continue to shrink and will likely leave minimal scarring in the end.  Try not to worry, allow your body to continue to heal, and I think you will be pleasantly surprised.

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.