The vocal folds are amazing in their capability of reacting to emotions and the finest feelings. There are mechanoreceptors in the tissue of the vocal folds and one would never really guess how much intricate emotional changes can affect the status of our vocal mechanism. Neither do we need to, in fact, I mean, scientifically. Let the scientists measure those. Enough for us to understand that the larynx is really sensitive.
What we do need to understand as singers, is that the vocal folds can behave in various ways and that we should be able to control them consciously to help our voices stay in good shape. I´m talking about the mechanism that determines if the folds are vibrating with thick or thin mass. The way to protect your voice from excessive workload is to be able to vibrate with thin mass. Only the edges of the folds come into contact. The sound is what we also call head voice or head register. This calls for gentle closure of the cords, even airflow and regulated air pressure. If you can do it, great, you are safe! Because if you no longer can sing softly, you may have a problem. The cords may have become too thick and are perhaps swollen; there might even be some tissue damage (the much feared nodules).
So, always cultivate your ability to sing pianissimo! Evenly, gently, smoothly – both low and high range, but especially in the middle range. If you have a nice mixed voice in the middle range, you also have vocal protection.
This doesn´t mean you should always sing softly – naturally you also need your fortissimo at times. The best exercise for this control is always the messa di voce – the old Italian concept of starting pianissimo and swelling it to full forte, and then back again to piano. Practice this and you gain great control for both your vocal folds and your breathing mechanism.