The nasal cavity contains two air passages extending between each nostril and the nasopharynx. It allows warming and humidification of the air before it enters the lungs. It also contains the organ that allows us to smell. If the nasal cavity is congested or blocked as with a cold or allergy it can affect tonal character of the voice. Increased nasal resonance (nasality) is often used as an artistic choice in commercial singing styles to alter tone and sound colour. It is almost never used in classical singing which requires a darker sound color.