I've heard from singers (I'm primarily a guitarist) that it can be dangerous to try to make your voice deeper because you might develop "nodules". Is it true? What are they? How can you avoid them?
Vocal cord nodules are benign (noncancerous) growths on both vocal cords that are caused by vocal abuse. Over time, repeated abuse of the vocal cords results in soft, swollen spots on each vocal cord. These spots develop into harder, callous-like growths called nodules. The nodules will become larger and stiffer the longer the vocal abuse continues.
Some general guidelines to avoid vocal problems:
All in all I don't think it's that simple to develope nodules (just by making your voice deeper). Toning and balancing your vocal output is part of the game as long as you do it the right way. A similar issue is Tenonditis for drummers. You can't say you will develop tenonditis if you play really loud. You probably will if you try to play loud without the proper technical training though.
I think that it is possible for anyone to develop nodes, but it's more about whether you care enough to try not to encourage it. Also, some people try to avoid people who might have it but it should be understood that nodes aren't contagious. You can't catch them per se, but you do have just the same chance of getting them as that person who has them, just by stressing your voice. But some simple ways to avoid them are to gargle salt water and just try to avoid stressing your voice any further.
If you hear someone with what we call a "gravelly" or "raspy" voice, it is likely that this person has pronounced vocal nodules.
Singing and speaking are muscular, athletic activities, and the parts of the body that produce the voice can suffer injury and cumulative damage just like the muscles and joints of a football player, or any other athlete.
It's true that some rock, pop and folk singers actually cultivate a raspy, gravelly voice. Whether they know it or not, they have adopted habits that have given them vocal nodules, which means they have caused permanent damage to their vocal folds.
Vocal nodules do not only occur in singers. They have historically been called "teachers' nodes" because they are common in schoolteachers, who lecture classrooms all day and sometimes have to shout over a noisy group of children.
Vocal nodules permanently degrade the quality of the voice and the ability to speak or sing loudly without pain. In extreme cases they can bleed; it is believed that Enrico Caruso, the most famous opera singer in all of history, died from acute bleeding in his larynx caused by a lifetime's accumulation of vocal nodules.
Most people that get vocal nodules, particularly if they are not singers, never get any medical treatment for them. The quality of their voice has changed over time, and they just deal with it.
If your doctor diagnoses you as having vocal nodules, the first treatment is for you to agree not to sing or speak at all (or as little as you can possibly get away with) for a period of weeks. This certainly means no rehearsing singing, and no performing. The nodules don't go away, but rest will reduce the inflammation and pain, and with training, it's possible to learn to modify your singing technique so that you will minimize additional damage to your vocal folds.
It used to be that extreme cases of vocal nodules were treated surgically by cutting them out with a knife, which invariably left scarring. These days they can be excised by laser beam, but there is always some permanent scarring one way or another. After surgery, a person is counselled to go through voice lessons with a teacher who is trained in rehabilitative therapy for the voice.