Sinusitis is an infection of the tissue lining your sinuses which are structures inside your face filled with air. When you have bacterial infections, viral infections and allergies, the sinuses are affected which then gets blocked and filled with fluid. Sinusitis can cause nasal congestion, pressure, pain in your pain and several other symptoms. While sinusitis can be a problem at any given time of the year, it can get worse during winter. The cold weather tends to trigger the symptoms of si