Sinusitis is an inflammation of the mucous membranes inside the nose and sinuses. Sinuses are the hollow spaces in your skull around the eyes and nose. Sinusitis causes pain and pressure in your head and face along with a stuffy or blocked nose. It can also cause thick, discoloured drainage from the nose or down the back of the throat. Children often also have a cough. Sinusitis can be acute (short-term) or chronic (long-term). Chronic sinusitis lasts 12 weeks or longer.