Sinuses begin as pea-sized pouches extending outward from the inside of the nose into the bones of the face and skull. They expand and grow through childhood into young adulthood.
Sinuses are part of the nasal air and membrane system that produces mucus.
Normally, the nose and sinuses produce between a pint and a quart of mucus and secretions per day. This mucus passes into and through the nose, sweeping and washing the membranes, picking up dust particles, bacteria, and other air pollutants along the way. The mucus then flows backward into the throat where it is swallowed, down into the stomach where acids destroy any dangerous bacteria. Most people do not notice this mucus flow because it is just a normal bodily function. This will be a clear, watery, and profuse mucus that is supposed to wash away the irritation or allergy.