Under eye bags and dark circles are a common complaint and are usually caused by a combination of several factors. These factors include increased pigmentation in the area, increased blood vessels in the area, fine lines and wrinkles, and periocular volume loss.
Often times, the main contributors are mild volume loss and increased pigmentation. These two issues can be addressed with injectable fillers and laser respectively.
Fillers will need to be re-injected every 6 months or so to start until a level of satisfaction is achieved, then used on an as-needed basis. Good luck!