I commonly have allergic symptoms on the airbus after 8 or so hours on board. Its is definately dust and other particles in combination with dry air. If you've ever spend time in a plane with cockpit humidification ( yes it is a Boeing and Bus manufacturer option ) you would immediately notice the difference.
My solution is to carry anti histamines and have one when starting to feel iffy. Engineering should clean more often - I often wonder if the air filter systems on these jets get cleaned as they should......