What is Mental Illness and How Does it Impact Behaviour?

Mental illness impacts how we think, feel and behave in daily life. For some individuals with mental illness may increase the likelihood of challenging behaviour incidents. By understanding mental illness it can give insight into the significant psychological disruption which creates significant challenges which then drives the emotional and behavioural difficulties. This short article looks at the relationship between mental illness, psychosocial disability and behaviour patterns.

a variety  of mental illnesses illustrated
This blog explores techniques and ideas that come from the Positive Behaviour Support Framework which you can read more about here

What is mental health?

The World Health Organisation (WHO) defines mental health as ‘a state of wellbeing in which the individual realises his or her own abilities, can cope with the normal stresses of life, can work productively and fruitfully, and is able to make a contribution to his or her community’ (WHO 2002). 

Why is mental health important?

Mental health helps us adapt and manage in times of change and uncertainity; cope with stresses of daily life; build and maintain good relationship with others; engage and participate in the world and make healthy choices. Mental health is important across the lifetime. Mental health can vary at different ages and stages of life. 

What is mental illness?

Mental illness (also called a mental health disorder) is characterised by clinically significant disturbance in an individual’s thinking, feeling, mood, and behaviour. Examples include Anxiety disorders, Bipolar disorders, Borderline personality disorder, Depressive disorders, Eating disorders, Obsessive compulsive disorder, Post traumatic stress disorder and Schizoid disorders

The overall causes of mental health issues are as varied and nuanced as the symptoms of many of the conditions themselves and tend to be eschewed in favour of classifying traits that present as indicators of higher risk for mental health disorders. 

Below are some of the varying elements that may influence someone’s risk for developing a mental health disorder.

Factors that influence mental illness

1. Genetic factors: Many disorders, such as depression and anxiety, are linked to a family history of the condition.

2. Biological factors: Many disorders are due to chemical imbalances in the brain.

3. Environmental factors: Environmental risks for mental illness can begin as early as the womb, with factors such as parental age, health, nutrition, alcohol and drug use affecting fetal development throughout pregnancy.  Social influences such as abuse, neglect, and/or trauma such as unstable, insecure relationships, defined by dysfunction, invalidation, abandonment and very poor living conditions in childhood have been shown to increase the risk of mental illness in adolescence and adulthood; psychologically, these issues can pave the way for social, emotional and learning delays; cause disordered attachment between children and caregivers; poor understanding of relationships with a great deal of difficulty making and keeping friends.

4. Social behaviours:  Mental health disorders such as schizophrenia, anxiety, depression, and psychosis have been associated with drug use throughout life, particularly in adolescence when the brain continues to develop and teenagers are increasingly susceptible to social and peer pressures. While cannabis has been linked to mood disorders and depression, disorders such as schizophrenia are more strongly correlated with the use of substance such as amphetamines.l.  

5. Chronic pain or disease: Individuals living with long-term medical conditions have a higher risk of developing a mental disorder such as depression, often due to stress from symptoms and the overall management of a serious illness. Medications for managing illness can also have undesired side effects on a patient’s mental health, coupled with negative lifestyle changes such as new or increasing pain, isolation or reduced social activity, fear, and emotional stress. 

Mental disorders can stem from multiple sources in an individual’s life, and in many cases arises from a combination of overlapping elements rather than a single root cause. Modern research on prevention, screening, and diagnosis of mental disorders has moved towards a layered model that incorporates markers from the biological, social (or environmental), and psychological factors affecting a person’s overall health.

The relationship between psychosocial disability and mental illness

Psychosocial disability is a term used to describe the disabilities that may arise due to a diversity of mental, emotional, social or cognitive experiences related to mental disorders (Ringland et. al, 2019). 

While not everyone with a mental illness will experience psychosocial disability, those that do experience severe psychological effects and social disadvantage due to the functional impact and participation barriers related to their mental disorder (NMHCCF, 2011). Psychosocial disability may impair a person’s ability to be in certain types of environments, think clearly, have enough stamina to complete tasks, cope with time pressures and multiple tasks, interact with others, understand constructive feedback and manage stress. This can lead to problems in engaging, participating and functioning in opportunities such as education, social situations, work, and achieving their goals and aspirations.  

Without adequate support, psychosocial disability can exacerbate mental disorders and negatively impact the person’s quality of life. Quality of Life (QoL) is a multidimensional concept that comprises of interpersonal relationships, social inclusion, personal development, physical well-being, self-determination, material well-being, emotional well-being, rights, living environment, relationships, recreation, education, employment and safety/security (WHOQoL, 1995).

Mental illness and impacts on behaviour

Challenging behaviour (behaviours of concern) can occur in the absence of mental illness and not all people with mental illness exhibit behaviours of concern (Xeniditis, Russell & Murphy, 2001). However, for some individuals with a mental illness, there is an increased likelihood of challenging behaviour incidents. Understanding mental illness can give an insight into the significant psychological disruption that create significant difficulties which then drives the emotional and behavioural difficulties. For example, according to the Diagnostic and Statistical Manual of Mental Disorders-5 (DSM-5), Borderline Personality Disorder (BPD) is a type of personality disorder that is diagnosed by a pervasive pattern of instability of interpersonal relationships, affective instability, impulsivity, intense and inappropriate anger and suicidal and self-mutilating behaviours. Individuals with a BPD diagnosis typically have interpersonal relationships that are chaotic, explosive, stormy and unstable. Intimate relationships are established rapidly and with intensity, often characterised by idealisation or devaluation, and intense fear of abandonment. Frantic efforts to avoid real or imagined abandonment and rejection, can result in self injurious behaviours and dissociation or paranoid ideation during stressful periods. Individuals with BPD experience their extreme emotions as reactions to events or interpersonal difficulties and feel helpless or unable to control the intensity of their feelings. These are expressed as bitterness, physical aggression, hostility, accusations but more prominently as depression, dysthymia, emptiness and loneliness they are unable to tolerate (APA, 2013). By understanding the mental health symptoms and how they affect a person's thinking, perception, mood or behaviour can help assist with devising a tailored treatment plan.   

Mental health treatment

Mental health professionals often adopt a biopsychosocial model for evaluating patients, using a combination of tests and metrics to assess different aspects of a person’s mental and behavioural patterns before making a diagnosis of mental disorders. A comprehensive history of each of the biological, pscyhological and social factors is collected, to allow clinicians more information for providing mental health treatment and support options that have a quality of life focus. 

Treatment options to improve mental health include medication and providing regular psychological support through a therapeutic approach that matches the individual's needs. Examples of different therapies include: Rational Emotive Behaviour Therapy (REBT), Cognitive Behaviour Therapy (CBT), Dialectical Behaviour Therapy (DBT), Psychodynamic therapy, Behavioural Therapy and Humanistic Therapy.  These therapies help the individual develop awareness and skills that thelp them realise their own abilities, develop emotional regulation skills to cope with stresses of life, and engage in activities that promote wellbeing.  

To target behaviours of concern, a comprehensive positive behaviour support plan (CPBSP) is useful. The CPBSP aims to collate a range of strategies and approaches that can be used by the individual and their support team to enhance the quality of life for both the individual and those that support them. This can be done through: teaching appropriate alternative behaviours; building independent living skills; developing social skills; accessing community programs; improving physical health; increasing engagement in activities that give life meaning and enjoyment; and supporting involvement in social support groups and building connections.  


American Psychiatric Association (2013). Diagnostic and Statistical Manual of Mental Disorders (5th ed.). Arlington, VA: American Psychiatric Association.

National Mental Health Consumer and Carer Forum (2011). Unravelling Psychosocial Disability - Position Statement on Psychosocial Disability Associated with Mental Health Conditions. Canberra: NMHCCF.

Ringland K.E., Nicholas, J., Kornfield, R., Lattie, E.G., Mohr, D.C., Reddy, M. (2019). Understanding Mental Ill-health as Psychosocial Disability: Implications for Assistive Technology.  ASSETS, Oct; pg. 156-170.  

World Health Organisation (2001). Strengthening Mental Health Promotion (Fact Sheet No. 220). Geneva: World Health Organisation. 

World Health Organisation (2004). Promoting mental health: concepts, emerging evidence, practice (Summary Report). Geneva: World Health Organisation; 2004.  

WHOQOL Group, WHO, Div of Mental Health, Geneva. (1995). The World Health Organisation Quality of Life Assessment (WHOQOL): Position paper from the World Health Organisation. Social Science & Medicine, 41(10), 1403–1409.

Xeniditis, K., Russell, A., & Murphy, D. (2001). Management of people with challenging behaviour. Advances in Psychiatric Treatment, 7(2), pg. 109-116.


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