Headache. Nonstop sneezing. Stuffy nose. Fatigue. If you're an airborne allergy sufferer, these symptoms are your constant companions for several months every year.  For those with year-round allergies, each day brings a cycle of misery, often broken only temporarily by powerful drugs—antihistamines and decongestants—often with side effects more uncomfortable than the original symptoms. Airborne allergies usually affect the respiratory system. Some airborne allergies, like the one we call hay fever, are seasonal.