Upper respiratory tract infection. Illustration of a human head with cutaway areas showing the processes involved in an upper respiratory tract infection (URTI). Examples include rhinitis (inflamed nasal membranes). The conditions shown here are inflammation of the paranasal sinuses (sinusitis), and a middle ear infection (otitis media). Mucus (yellow) is seen accumulating and flowing within the sinuses, and in the middle ear and the Eustachian tube (connecting the ear to the throat). The cochlea (pink) is shown in the ear. The frontal sinus is at top (in the forehead), the ethmoidal sinuses are between the eyes, and the maxillary sinuses are in the cheekbones.