Whats up with that sudden sneezing, stuffy nose, or sinus pressure? Your sinuses probably are reacting to an irritant or infection. The nose and the sinuses are the first line of defense for your respiratory system, says Joseph E. Kelleher, MD, a specialist in allergy and immunology at the Lahey Clinic in Burlington, Mass. They are lined by the mucociliary transport system, which consists of mucous membranes and the tiny, finger-like projections known as cilia; their purpose is to warm, moisten, and filter the air you breathe. The membrane does this by producing mucus that traps irritants. Then the cilia move the mucus, along with any trapped irritants, out of your sinuses. Anything you can do to keep the respiratory system healthy can help prevent sinus problems, adds Dr. Kelleher.