A polyp is a growth (usually benign) protruding from a mucous membrane. When polyps are seen over vocal cords they are called as vocal polyps or vocal nodules.
Vocal cords are like two strings present in the voice box (larynx) and are absolutely essential for phonation. Nodules on the vocal cords interfere with normal voice functioning and produce a hoarse, breathy or weak voice.
Vocal nodules develop from various reasons ranging from voice overuse (such as prolonged singing, shouting or loud talking) or cigarette smoke, viral infection, or chronic inflammation and sinusitis. Moreover, it is believed that polyps or nodules are an allergic inflammatory reaction. Allergy is an altered state of normal immunity that overreacts to otherwise harmless agents.