A couple of months ago when I had my annual physical, I asked my doctor about the dark circles under my eyes. She took one look at me (knowing my medical history) and said, "Oh, those are allergy shiners."
Apparently they happen when you take allergy medicine, specifically the same brand, for too long without switching. So I take off-brand products from Costco, but she recommended that I switch between the off-brands of Allegra, Zyrtec, and Claritin every two months. Still waiting to see if there is improvement.
I am thinking that perhaps some of it is also caused by my early morning hours for seminary. A friend said, "but you always get up that early!" My reply, "I would not get up that early if I didn't have to now."