Most hoarseness is from a viral cold and settles in a week. A voice change lasting more than three weeks, especially in a smoker or anyone over 40, always needs to be looked at — usually with a quick flexible laryngoscopy in the clinic. Most causes are benign; finding the few that aren't, early, matters.
The voice is produced by the vocal cords, two small folds of tissue that vibrate as air passes between them. Anything that changes their shape — inflammation, a nodule, a polyp, a paralysis — changes the voice.
Common benign causes are vocal cord nodules (teachers, singers), polyps, reflux laryngitis, and acute viral inflammation. The serious causes — vocal cord paralysis or laryngeal cancer — are far less common but worth excluding promptly in any persistent change.
Any hoarseness lasting more than three weeks should be assessed. Bring it forward if you have lost weight, are coughing up blood, have difficulty breathing or swallowing, or have noticed a lump in the neck.