Harmful habit it automatically repeating many number of time action, and action it вредоносное from the point of view of the public boon environmental or health the man, which has fallen under servitude of a harmful habit.
The harmful habits are not useful or directly вредны. Such automatic actions are shown because of weakness of will. If the man can not show force of will to make progressive action, he falls under force of a habit, which returns it(him) in an old track, habitual action.
The habitual action is and there is a habit. But, on the one hand, there are habits and manners good, useful and, to another, are be bad, or harmful habits.
As useful habits we can name such how do(make) зарядку on mornings, wash hands before meal, clean(remove) behind ourselves all things on a place, clean each day teeth etc.