The upper respiratory system includes the nose, nasal cavity, pharynx, and larynx with subglottic area of trachea. In the normal circumstances, air enters the respiratory system through nostrils where it is filtered, humidified and warmed inside the nasal cavity. Conditioned air passes through pharynx, larynx, and trachea, and then enters in lower respiratory system. Dysfunction of any part of upper respiratory tract may change quality of inhaled air, and consequently may impair function of tracheobronchial tree and lung. Upper respiratory tract infections are the most common infections in population. They are the leading cause for people missing work or school, and thus have important social implications. They also range from the mild, self-limited disease like common cold, syndrome of the nasopharynx to serious, life-threatening illnesses such as epiglottitis. Most of those infections are of viral origin, involving more or less all the parts of upper respiratory system and associated structures such as paranasal sinuses and middle ear. Common upper respiratory tract infections include: rhinitis - Inflammation of the nasal mucosa, rhinosinusitis or sinusitis - inflammation of the nares and paranasal sinuses, including frontal, ethmoid, maxillary, and sphenoid , nasopharyngitis (rhinopharyngitis or the common cold) - inflammation of the nares, pharynx, hypopharynx, uvula, and tonsils, pharyngitis - inflammation of the pharynx, hypopharynx, uvula, and tonsils, epiglottitis - inflammation of the superior portion of the larynx and supraglottic area, laryngitis - inflammation of the larynx, lryngotracheitis - inflammation of the larynx, trachea, and subglottic area and tracheitis - inflammation of the trachea and subglottic area. In most cases these diseases are self-limited, managed at home. The more severe cases , or those with complications seek medical help. The symptomatic therapy is offered (analgesics, antipyretics, anticholinergic agents, antihistamins, antitussives, adrenergic agonists, corticosteroids, decongestants), in some instances antibiotics, or some traditional way of cure. In some instances surrgical intervention is necessary or in most serious cases care in intensive care unit.