Why do we lose our voice?

On sounding sweet, or not: There is such a thing called singer’s nodes, which are similar to calluses, but only on your vocal cords Three years ago, Adele underwent surgery to remove a benign polyp of her vocal cord. — EPA

Hoarseness of voice is a common occurrence and can be due to many reasons.

My sister lost her voice recently. She was having a sore throat, and then yesterday, she couldn’t speak at all. She was due to give a presentation at her office and someone else had to take over. How can one lose one’s voice?