Institute of Epidemiology & Health Care


Science of Habits

A lot of research has been done on habits - what habits are, how we form them, and if they can be used to help people improve their health. The information below summarises what this research has found.

What is a habit?

Many healthy lifestyle programmes use the term 'habit' but few are based on habit theory.

When people talk about 'habits' in everyday life they often just mean something they do all the time.
But according to psychological theory, a habit is only a habit if it as an action that happens automatically when we encounter a certain setting or situation in which that action has been performed in the past.

A key aspect of habits is that because they are automatic, they override intentional behaviour. This means that as a habit becomes stronger, it becomes harder to perform a different action, even if you intend to do so.
Habits are therefore likely to persist over time; because they are automatic and so do not rely on conscious thought, memory or willpower.

How do we form a habit?

In order to form a habit, an action must be performed repeatedly in a consistent context.

This repetition creates a mental association between the context (cue) and the action (behaviour) which means that when the cue is encountered the behaviour is performed automatically.


For example, imagine that, each time drink a cup of tea, you eat a biscuit. When you first eat a biscuit with your cup of tea, a mental link is formed between the context (drinking a cup of tea) and your response to that context (eating a biscuit).

Each time you subsequently have a biscuit in response to having a cup of tea, this link strengthens, to the point that having a cup of tea makes you reach for a biscuit automatically, without giving it much prior thought; a habit has formed.


It is essential that something about the setting where you perform the behaviour is consistent so that it can cue the behaviour, but it doesn't have to be too specific. For example, if you want to form a habit for having a piece of fruit after lunch, it probably doesn't matter if you eat lunch at different times in the day.

How long does it take to form a habit?

It takes up to 10 weeks to form a new habit

A common myth is that habits take 21 days to form. This appears to have originated from anecdotal evidence about the adjustment period for plastic surgery but does not relate to habits as we know them.

More relevant research has shown that it takes 66 days (up to 10 weeks) on average to form a new habit after the first time the new action is performed, but this can vary from person to person and for different actions.


For example one study found that one person took just 18 days to form a habit, whereas others took much longer. Similarly, forming habits for simple behaviours (such as drinking a glass of water) was a lot quicker than for more complex behaviours (e.g. doing 50 sit-ups). There are also differences in how strong habits become for different actions.

Second nature

However long it takes, doing the action does get progressively easier; research suggests if you do keep up the action until a habit is formed, it will eventually become 'second nature. Research also shows that missing an opportunity to perform an action does not significantly impact the habit formation process, so don't be discouraged if you slip up- just try to get back on track as soon as you can.

Can habits improve health?

Yes. A number of studies have demonstrated that habits can be used to help people engage in positive health behaviours.

In these studies, habits are measured using a self-report measure of automaticity (Verplanken and Orbell's Self Report Habit Index (2003)). For example, participants rate how much they agree with the statement 'I do this without having to consciously remember' for their chosen action.


One study asked ninety-six volunteers to choose a single healthy action and to repeat it in a consistent context (e.g. 'doing 50 sit ups after their morning coffee'). Participants reported the automaticity of the behaviour on a daily basis and as time went on the automaticity of the behaviour increased until it levelled off and a habit was formed. Once a habit was formed, this increased the likelihood that the behaviour would be performed in the future.

Since then, the habit model has been used to design effective interventions to encourage weight loss, to promote healthy eating in children, to reduce older adults sedentary time, and to increase flossing. ASCOT is the first study to apply this model to a healthy lifestyle programme for people diagnosed with cancer.

Want to read more about the science behind habits?



If you are interested in more of the science behind habits, below are some papers you can download to read.

Lally, P., van Jaarsveld, C. H. M., Potts, H. W. W., & Wardle, J. (2010). How are habits formed: Modelling habit formation in the real world. European Journal of Social Psychology, 40, 998-1009.

Lally P, Wardle J & Gardner B. (2011): Experiences of habit formation: A qualitative study, Psychology, Health & Medicine, 16:4, 484-489

Gardner, B; Lally, P; Wardle, J; (2012) Making health habitual: the psychology of 'habit-formation' and general practice. Br J Gen Pract , 62 (605) 664 - 666.