a sinus infection occurs when a pathogenic organism (virus bacterium or a fungus) grows within a sinus and causes intermittent blockage of the sinus ostium. drainage of mucus and pus often occur when the blockage is relieved. the drainage usually goes from the nasal passages to the throat or out the nostrils. such infections also cause inflammation (an influx of immune cells and swelling of the sinus tissue) of one or more sinuses. this adds to blocking the openings of the sinuses and causes discomfort. inflammation of the air cavities within the passages of the nose (paranasal sinuses) is referred to as sinusitis. sinusitis can be caused by infection but can also be caused by allergy and irritation of the sinuses. sinusitis is one of the more common conditions that can afflict people throughout their lives. sinusitis commonly occurs when environmental pollens irritate the nasal passages such as with hay fever. sinusitis can also result from irritants such as chemicals or the use and/or abuse of over-the-counter (otc) nasal sprays and illegal substances that may be snorted through the nose. about 30 million adults have "sinusitis. "
what is a sinus infection?