What could be causing the dark circles under my eyes when asthma acts up?

Depends: It may be from a lack of sleep. The eye is commonly involved in allergic reactions. The conjunctiva is the part of the eye most frequently affected.

Allergic shiners: Or lack of sleep. Allergic shiners are signs of allergic rhinitis (see photo). Allergic rhinitis often accompanies asthma. If asthma is keeping you up at night those dark circles may just be due to lack of sleep.