How to know if you have hurt your voice
Most vocal damage happens from a combination of three different reasons: misuse, abuse, and overuse.
For the most part misuse is something that you can certainly fix with the help of a good teacher. A good teacher can guide you back to where your voice sings best and help you break old habits that you know are messing with your voice and causing bad technique. Check out some of the other articles here and maybe you can find something that you need!
In terms of overuse, you have to make sure you find enough time to rest your voice, body, and mind. A healthy person paves the way for healthy usage of the voice. The healthier your voice, the longer you can sing for before it starts getting tired or foggy. Even the best singer in the world can’t sing forever. I have found that singing much more than 6 hours in a day doesn’t really help you.
If you are just starting out, sing for 30 minutes or until you feel a little tired. Then one day, if it feels really good, sing for an hour or so. Sooner or later you will find yourself in a group singing for a two or even three-hour rehearsal. Then the game becomes about how to preserve your voice. If you can go a long time (longer than 6 hours), you still feel great, and its not getting in the way of your social life, then do it by all means!
Abuse is where a lot of real damage can occur. This can happen as a choice as well as by accident. Lots of partying, screaming, or singing when it hurts and feels hard to do can lead to a hoarse voice. If you do this enough times in a row without any vocal rest, it becomes a chronically hoarse voice. In some cases, people will in a singular event (like a particularly loud scream at a sports game) cause themselves an immediate loss of voice for an extended period of time. If this happens and or you hear a pop, accompanied by intense pain, then you want to go to the Emergency Room right away! Often times this is a result of a sudden massive vocal fold hemorrhage (burst of blood vessels in you vocal chords). You don’t spit out blood or anything as it’s most often like a really bad bruise. Nevertheless, it is a medical emergency that can cause permanent damage if it is not treated as soon as possible.
If you catch this early, then much of the long-term damage can be reversed.
Imagine what life would be like if you couldn’t use your voice to express yourself. If you suddenly went blind for a few days, I bet you would rush to the ER. Much better to be safe than sorry!
Also, if you notice a chronic pain, can’t sing softly in your middle range at all, or find that there are rough spots in your voice that don’t get better, then I would say you would benefit from getting an appointment with an ENT (Ear Nose and Throat Doctor). There is always a chance that it is a vocal node, which an ENT will be able to tell you very quickly. A vocal node is a callous (sort of like the ones that guitarists get on their fingers) that forms on the vocal fold from repetitive trauma. It gets in the way of singing, and causes the vocal folds to wobble/not vibrate efficiently. This will make it harder and harder to sing and the sound becomes permanently foggy sounding. A node however, can go away with extensive vocal rest (we are talking about up to 6 months or more of not singing). It is best to hear an estimation of how long to rest from an ENT though as they will be able to directly see your vocal folds and diagnose you from there. Only in serious cases is surgery necessary with a nodule.
In some cases, vocal damage is for a reason entirely outside of what you are doing vocally. If you are sure you aren’t doing any of these three things: misuse, abuse, and overuse, then getting it checked out is a good idea. The ENT will most likely use a laryngoscope (tube-like camera that goes in through the nose) and look in at your vocal chords. There are a lot of medical problems that can seriously affect your voice and rather than list them all here, I would advise you to not try and self diagnose, but just be aware of what your body is telling you and seek advise from a medical professional when you are concerned.