Sinusitis, also known as rhinosinusitis, is inflammation of the mucous membranes that line the sinuses resulting in symptoms that may include thick nasal mucus, a plugged nose, and facial pain. Other signs and symptoms may include fever, headaches, a poor sense of smell, sore throat, and cough. It is defined as acute sinusitis if it lasts less than 4 weeks, and as chronic sinusitis if it lasts for more than 12 weeks.