The vocal cords are structures that vibrate. and with complex movements of your throat and mouth you are able to create your voice. When there is any change in the ability of these vocal cords to vibrate, the voice will also change resulting in hoarseness. There are many reasons for hoarseness but the most common condition is secondary to some type of viral or upper respiratory infection that causes some swelling of the vocal cords temporarily (laryngitis). With time, this type of hoarseness should completely resolve.
Overuse of the voice can sometimes result in prolonged hoarseness secondary to vocal cord nodules and these are known as singers or screamer's nodules. Other causes of prolonged hoarseness may be secondary to inhaling toxic substances, smoking, acid reflux, paralysis of a vocal cord, and other types of growths on the vocal cords. If you have hoarseness lasting more than 3 weeks, you should see an Ear, Nose and Throat specialist.