Think of when someone says, 'Stop being so aggressive!' This means the person is putting too much hostility, force and violence alttitude. This gives you an idea of what aggression means.
Since you know what aggression means, aggression can lead to these followings:
Anxiety in most cases. Violence Sucide / homicide. Anger Irritablity. Fear. Steriods.
And many others that you can think of. All these are negative emotions which is bad for your health. People with such disorders needs a psychologist immidiately IF required.