Over-use of antibiotics and cortisone sprays has led to more virulent forms of bacterial infections as well as new fungal infections of the sinus cavities. Asthma and allergic disorders often cause chronic inflammation of the nasal mucosa, resulting in chronic sinusitis. About 20% of patients with chronic sinusitis may develop nasal polyps, cyst-like growths that develop from sinus tissue and may further obstruct the sinuses.