Mental Health refers to a person's psychological and emotional functioning, including how they experience emotions, think, relate to others, cope with challenges and participate in everyday life. It is broader than the absence of a diagnosed mental disorder and can vary over time in response to biological, psychological and social influences. Mental health exists across a continuum of experiences rather than as a simple division between completely healthy and completely ill states. A person can experience significant distress without meeting criteria for a particular disorder, while someone with a diagnosed disorder can experience periods of stability and effective functioning. Mental health therefore encompasses wellbeing, functioning, distress, resilience and clinically significant psychological conditions.
Mental disorders are conditions involving clinically significant disturbances in cognition, emotional regulation or behaviour that are associated with substantial distress or impairment, subject to the diagnostic framework being used. Major diagnostic categories include depressive disorders, anxiety disorders, bipolar disorder, psychotic disorders, obsessive-compulsive and related disorders, trauma-related disorders, eating disorders, personality disorders and neurodevelopmental conditions, among others. Diagnostic systems such as the International Classification of Diseases and the Diagnostic and Statistical Manual of Mental Disorders provide structured criteria, but diagnosis is not equivalent to identifying a single biological laboratory marker. Assessment commonly involves history, observation, structured or unstructured clinical interviews and consideration of functional impact, duration, severity and alternative explanations.
Mental health is influenced by interacting biological, psychological and social factors. Genetics, brain development, physical illness, sleep, hormones, substance use and medication can affect psychological functioning, while trauma, relationships, employment, housing, financial circumstances, discrimination, social isolation and other environmental factors can also influence mental wellbeing. This multifactorial model does not mean that every mental health condition has the same cause or that social circumstances alone explain psychiatric illness. It instead recognises that mental health outcomes often emerge from interactions among vulnerabilities, protective factors and experiences over time. Public health approaches therefore address both individual treatment and wider determinants that influence population mental health.
Depression illustrates the difference between ordinary emotional responses and a mental disorder. Sadness is a common human emotion and can occur after loss or disappointment, whereas depressive disorders involve a broader pattern of symptoms that may include persistent low mood or loss of interest together with changes in sleep, appetite, energy, concentration, self-worth or psychomotor activity. Clinical assessment considers symptom duration, severity, functional impairment and differential diagnoses.
Anxiety similarly ranges from normal responses to threat or uncertainty to disorders in which fear, worry or avoidance become excessive, persistent or significantly impairing. The distinction depends on the pattern and consequences of symptoms rather than on whether a person has ever felt sad, worried or afraid.
Psychotic disorders involve disturbances such as hallucinations, delusions and disorganised thinking or behaviour, although presentations vary substantially. A hallucination is a perception occurring without an external sensory stimulus of the corresponding type, whereas a delusion is a strongly held belief that persists despite evidence inconsistent with it. Psychosis can occur in several psychiatric and medical contexts, including schizophrenia-spectrum disorders, severe mood disorders, substance-related states and some neurological or medical conditions. Assessment therefore needs to consider physical health, medication and substance use rather than assuming that every psychotic symptom represents the same disorder. Early assessment can be important because untreated severe symptoms may significantly affect safety, functioning and social participation.
Mental health treatment includes psychological therapies, medication, social interventions, rehabilitation and practical support, often in combination. Cognitive behavioural therapy, for example, addresses relationships among thoughts, emotions and behaviours and has applications across several conditions. Antidepressants, antipsychotic medicines, mood stabilisers and other medications have different indications and risks and should be selected according to the person's clinical circumstances. Treatment may also involve occupational rehabilitation, family interventions, supported housing, substance-use treatment and crisis services. Evidence-based care does not imply that one intervention works for everyone; response, side effects, preferences, comorbidities and access to services all influence treatment planning.
Prevention and early intervention are important because mental health difficulties can affect education, employment, relationships, physical health and life expectancy. Protective factors can include stable relationships, social connection, meaningful activity, adequate sleep, physical activity, access to healthcare and supportive environments, although these factors do not guarantee protection against mental disorder. Stigma can discourage people from seeking help and can affect how mental health conditions are perceived and treated. Mental health literacy involves understanding symptoms, available support and the difference between common emotional experiences and conditions requiring professional assessment. Population approaches may include school programmes, workplace interventions, community services and policies addressing social determinants.
Mental health care also involves safeguarding, capacity, confidentiality and risk assessment. Clinicians may need to assess risks involving self-neglect, self-harm, suicide, violence, exploitation or inability to meet basic needs, while recognising that risk cannot be predicted with certainty from a diagnosis alone. Mental capacity concerns whether a person can make a particular decision at a particular time and should not be confused with having a mental disorder.
Confidentiality is an important professional principle, but there are circumstances in which information may need to be shared to protect a person or others, subject to applicable law and professional standards. Mental health services therefore operate at the intersection of clinical care, ethics, law, social support and individual autonomy.
