What causes strain or damage to the vocal chords?

Continual shouting or continual speaking at full volume. No, I think it is not permanent unless these episodes of laryngitis occur over and over.................. Did you notice Hillary's voice near the end of her campaign? She was struggling with hoarseness. I had a friend who was a cockswain for a crew team in college. She had to continually yell commands. She, too, was always struggling with hoarsenss. Smoking, too, but I am sure you don't do that.

Some good answers above. Please remember though, that this is not necessarily a bad thing! That's one thing the classically trained vocal teachers don't tell you. The most wonderful singers on the planet, for my money anyway, Etta James, Ray Charles, had/have that grit in their voice from abusing it a little. It sounds good! A little character imparted from some straining is not a bad thing, in fact it can be great. Remember that classically trained teachers won't tell you that... but they live in museums, make their living teaching people (who then go off to teach), and secretly fantasize about bringing the house down and turning people on with an improvised, sexed up,powerful R&B vocal performance. In music school, the jazz and funk guys worked the hardest.