Burnout is one element of the negative effects of caring that is known as Compassion Fatigue.
Most people have an intuitive idea of what burnout is. From the research perspective, burnout is associated with feelings of hopelessness and difficulties in dealing with work or in doing your job effectively. These negative feelings usually have a gradual onset. They can reflect the feeling that your efforts make no difference, or they can be associated with a very high workload or a non-supportive work environment.