singing voice

Changing pitch in chest voice is largely performed by tensioning the thyroarytenoid muscle. This is the muscle within the vocal cord itself. Changing pitch in falsetto is largely from the cricothyroid muscle. This muscle rests outside the larynx and rocks the 2 main cartilages of the larynx producing a change in length of the vocal cord. Consequently, we have 2 sets of muscles to change pitch. They tend to overlap in the middle of our vocal range and we can produce the same note in more than one way. That is, we can sing the note C4 (middle C) primarily by contracting our thyroarytenoid muscle, which would thicken and tighten the vocal cord while it remains the same length. This produces the rather full sound that you describe as chest voice.

Alternatively, we could tighten our cricothyroid muscle until we reached the note C4 and we would stretch the vocal cord longer and thinner until we reached this note. Even though we have 2 discrete ways to produce the same note, and you could do this on a guitar with 2 different size strings, the quality will be different when a thicker string vibrates at a given pitch then when a longer and thinner string vibrates at the same pitch. We could also produce the same pitch with some intermediate tension on each of these 2 muscles. Consequently there are many ways of creating the notes in the mid-range of our voice. A classical singer would typically spend years trying to smooth out this transition between using one muscle and the other. This would create a blend rather than a break as we shift the tension from one muscle to the other gradually.

In my experience, vocal elevations/swellings (nodules, polyps etc.) come from vocal overuse. Very few people sing sufficiently to create vocal swellings solely from singing. However, a great many people are extremely talkative and filled their life with vocal activity, both singing and speaking. The greatest factor for creating a vocal swelling is vocal overuse, talking too much. A person who is very talkative and hoarse has about an 80% chance of having a vocal swelling based solely on this information. The second factor contributing to vocal swelling is vocal volume. The third factor is likely vocal technique.

I think the use of chest voice or head voice (falsetto) plays almost no role in the formation of vocal swellings. Quantity mostly and volume second are the overriding factors creating lesions along the vibrating margin of the vocal cord.

The word laryngitis means inflammation of the larynx. If your larynx is inflamed, at some point it should become not-inflamed. You and your doctor would need to determine when that point is.

Whispering is much different than yelling. In a true whisper, the airway is narrowed and airflows turbulent leak through this narrow point. This generates white noise which we hear as a whisper. Consequently there is no movement of the edges of the vocal cord. This is in strong contrast to a yell where the vocal cords are hitting each other rather aggressively. There is an in-between sound called a stage whisper where the vocal cords are partially closed and partially allowed to vibrate. There is both a white noise quality and a pitch quality to a stage whisper.