In a 2009 study on rats, conducted by Rui Costa of the Champalimaud Foundation in Portugal, in collaboration with the National Institute of Health, they found that chronic stress acts as a trigger for old habits.
This is an important discovery because the key to habit change is awareness. Being aware of your habits is the stopgap that prevents you from engaging in destructive habits. If you are aware of the triggers that cause you to engage in bad habits, you can take action to avoid those triggers or to engage in activities that stop those triggers in their tracks, before they make you take action.
Chronic stress is caused by external environmental factors. These factors could be almost anything: a demanding boss, deadlines, monthly bills, family, friends, weather, etc.
You can feel stress as it is happening. Knowing this, there are things you can do to stop stress and, therefore, prevent bad habits from taking over your life.
For example, suppose deadlines act as a trigger for stress and when you feel deadline stress you have the bad habit of reaching for a cigarette. Procrastination, therefore, is the worst possible thing you can do. The solution is to tackle the project long before the deadline approaches. This will prevent the deadline stress trigger from occurring and thwart the bad cigarette habit.
Awareness of the bad habit triggers, helps you to take action to avoid those triggers and the corresponding bad habits.