I've described a local singer here who has a perfectly good natural voice, but who has developed the habit in singing in head voice and has all but abandoned singing unnecessarily because she can no longer handle long lines, gasps for breath and her singing actually peters out before she reaches the end of the line."
this could be rectified in my opinion by breathing exercises and stopping smoking, bad breathing can sometimes occur through incorrect posture, Alexander technique is designed to help perfrmers[including singers] perform better,
bad breathing is not necessarily anything to do with head voice, it can occur with singers who use chest voice too.