What Are Mental Health Disorders?

  • Finley HansenBSc, Neuroscience, Cardiff University / Prifysgol Caerdydd
  • Drew GallagherB.Sc. Biomedical Science with Modern Language (Japanese), University of Manchester
  • Saameh SanaaeeBachelor of Science - BS, Cell/Cellular and Molecular Biology, Islamic Azad University, Iran
  • Jessica TangBSc, Cancer Science, Oncology and Cancer Biology, University of Nottingham


Mental health is a general term that covers a broad range of areas related to the status and adaptability of someone's mind, including their current psychological well-being, how resilient they are to adverse events, and their motivation for tasks. As mental health comprises such a wide range of areas within one's life, it is highly influential in one's decision-making, outlook and overall satisfaction with life. It can also be impacted by a variety of factors, such as genetics, environment, life experiences and access to resources and support. Furthermore, these factors can interact to be individually protective or destructive to one's mental health.

A mental illness occurs when someone is not psychologically healthy and is a result of a mental health condition/disorder, such as depression, anxiety, schizophrenia or bipolar disorder. The presentation and experience of a mental health disorder varies depending on which disorder is present but typically involves significant distress and has knock-on effects on many domains within the person’s life. 

Types of mental health disorders

Mental health disorders encompass a wide range of conditions that often share core symptoms and underlying causes, yet there are important differences that allow categorisation, as shown in the table below. These are some of the most common mental health disorders, but it is not an exhaustive list. 

Category Core symptomsExamples
Mood disorders 

Persistent disruption in ‘mood’ as emotions are dysregulated. This causes emotional suffering and can disrupt one's ability to enjoy life and function within society. There may be intense ‘highs’ and or intense ‘lows’.1i) Depressive disorders
ii) Bipolar disorders (1 and 2)
iii) Seasonal affective disorder
Anxiety disorders Persistent and or excessive worrying/feelings of fear. These thoughts/feelings are often inappropriate for the situation and make many tasks difficult, often leading to avoidance and other unhelpful coping strategies.2i) Generalised anxiety disorder
ii) Obsessive-compulsive disorder
iii) Social anxiety disorder
Eating disorders An unhealthy relationship with food as it is used to manage one's feelings in a way that is mentally and physically dangerous. i) Anorexia nervosa
ii) Bulimia nervosa
iii) Binge eating disorders 
Psychotic disordersA distorted view of reality that may be associated with hallucinations, disorganised speech and disorganised behaviour.3i) Schizophrenia
ii) Schizoaffective 
Personality disordersExtreme personality traits cause psychological suffering and interfere with daily functioning, often including an inability to maintain healthy interpersonal relationships.4i) Borderline personality disorder
ii) Narcissistic personality disorder

Two caveats should be noted with this categorisation: 

1) Some conditions are hard to place in one category as they have features that fit numerous categories. For example, bipolar disorders can be considered as both mood and psychotic disorders and are often described in the literature as ‘psychotic mood disorders’. 

2) Many people are diagnosed with multiple conditions at once (this situation is referred to as comorbidity). For example, in the US, it has been documented that over 50% of the patients meeting the criteria for a diagnosis of depression also meet the criteria for a diagnosis of an anxiety disorder and so are given a ‘dual diagnosis’.5

Causes of mental health disorders

The causes of mental health disorders are a highly controversial and complex topic. While there are numerous factors that may contribute to the development of a mental health disorder, and there are different factors that increase the likelihood of developing different mental health disorders, you can divide these causes into 2 broad categories: 1) genetics and 2) environment

Our genetics are what we are born with, and these contain the biological instructions that make us who we are. Environmental factors comprise everything that happens to us outside of our genes, such as how we are raised, the influence of our peers, the effects of our diet, our lifestyle and all other events in our lives.

In regards to genes, while it’s understood that there is no single gene that single-handedly causes a mental illness, there are certain genes that increase the likelihood of developing mental illness, given certain environmental factors. This concept is where the famous term that every biologist knows comes from: ‘gene-environment interactions’. Understanding how our genes interact with our environment is key to understanding the cause of mental health disorders, as these two domains will almost always interact. Think of it this way: genes can’t have an effect on behaviour without the environment that they operate within.

Explaining all of the genetic and environmental factors that may contribute to developing a mental health disorder and their interactions is not only beyond the scope of this article but is also impossible, as many of these factors and their biology are not fully understood. Nevertheless, a famous example is a study looking at the influence of a gene controlling the way a brain chemical called serotonin works on the development of depression and its interaction with early life stress. It has been previously thought that having ‘low’ or poorly functioning serotonin can cause depression, and thus, having faulty genes that code for the way serotonin works would cause depression. However, studies have not consistently shown that simply having low serotonin will cause depression.

Despite these findings, in a different type of study, researchers observed a cohort of children at regular intervals as they grew up into adults, noting their genes at the start of the study and what happened to them throughout their lives. It was found that having a faulty gene for serotonin did not increase the chance of developing depression unless there were early life adverse experiences, such as child abuse and significant physical illness.7  This effect has since been replicated not only for depression but for other mental illnesses like anxiety, schizophrenia and bipolar disorder.8

In essence, some genes can make a person vulnerable to stresses in their environment. Like a house with a poor foundation in a hurricane, it’s a perfect storm.

Signs and symptoms of mental health disorders

The signs and symptoms of mental health disorders vary widely, but again, there are some core behavioral signs that are shared between disorders, so if someone is showing these, it may indicate that they are experiencing a mental health disorder.

  • Social isolation: is this person spending less time with friends and family?
  • Low energy/fatigue: does this person seem much more tired than usual? Are they sleeping for very long periods and/or throughout the day?
  • High energy/non-fatigue: does this person have significantly more energy than usual, to the point where they are hardly sleeping?
  • Psychomotor depression: is this person speaking and moving extremely slowly, almost like they are in slow motion?
  • Psychomotor excitation: is this person speaking and moving extremely quickly, almost falling over their own words, changing topics randomly and unable to sit still?
  • Irritability/aggression: is this person more intolerant than usual and easier to annoy?
  • Lack of interest in activities/decreased motivation: is this person spending less/no time engaging with past times they used to spend time doing?
  • Decreased work/academic performance: has there been a sudden drop in grades or performance at work?
  • Cognitive dysfunction/impaired decision-making: is this person having trouble understanding and following basic tasks?
  • Increased risk-taking: is this person deliberately putting themselves in dangerous situations?
  • Paranoia/loss of touch with reality: is this person convinced of nonsensical beliefs, such as being followed by aliens? 
  • Host of unexplained medical symptoms/conditions: has this person been complaining of unexplained pains and illnesses that doctors have not been able to identify causes for?


Doctors are trained to diagnose mental health conditions based on the signs mentioned above as well as other symptoms reported by the patient. Some or all of the signs mentioned above may be present in a patient and in different combinations, depending on the individual's experience and which condition they may or may not be suffering with. 

As unique combinations of symptoms and signs may be present, a doctor (usually a psychiatrist) will perform a ‘differential diagnosis’ which aims to differentiate between related conditions based on which symptoms are present or not, their severity, their frequency, duration and onset. Years of training and experience make them adept at differentiating between conditions using this method. 

Management and treatment for mental health disorders

The management and treatment of mental health disorders depend on which mental health condition is present, the severity of symptoms and where in the world you are. Generally, there are 3 main avenues for treatment: 1) psychological intervention (therapy), 2) medication and 3) inpatient care. These may be used in combination. Typically, a model of ‘stepped care’ (see diagram below) is used where more severe cases will need more staff, more specialists and more money to manage and treat, often involving stronger medication. 

Risk factors

Risk factors refer to certain life choices, habits, traits and genes that increase the chances of developing a mental health disorder. In a sense, they are the causes of mental health conditions, but as mentioned earlier, they do not singlehandedly cause mental illness; they just increase the risk of you developing one. There is a significant overlap of risk factors between mental illnesses, including the following:9

  • Chronic stress 
  • Traumatic experiences 
  • Family history of mental illness 
  • Substance abuse
  • Childhood history of abuse/neglect 
  • Previous mental illness
  • Ongoing chronic medical condition(s)
  • Homelessness/unemployment 
  • Social isolation 


Because mental health encompasses so many domains of life, having a mental illness can lead to far-reaching consequences. Individuals not only suffer directly from the condition but may also make decisions during their mental health challenges, leading to worsened and prolonged suffering. These are some of the potential consequences of mental illness:

  • Emotional suffering and decreased quality of life 
  • Substance abuse and addiction 
  • Family conflict
  • Legal and financial issues
  • Self-harm 
  • Weakened immune system and other medical issues
  • Social isolation 
  • Inability or struggle to form interpersonal relationships
  • A loss of academic and employment potential
  • Poverty and homelessness
  • Increased rate of mortality 


How can I prevent mental health disorders?

You cannot ensure against developing a mental health disorder as you cannot change your genetics or everything in your environment. However, you can increase your resilience and lower stress levels by:

  • Practising self-care
  • Staying physically healthy 
  • Paying attention to the warning signs 
  • Getting professional help when it is needed
  • Talking about your problems with a trusted person
  • Avoiding drug misuse

How common are mental health disorders?

While the proportion of people suffering from a mental health disorder may vary by country and by time, the WHO estimates that around 1 in every 8 people was living with a mental health disorder in 2019. This is likely to have increased after covid by around 20%. For a breakdown of how common each disorder is, see this table.11

What can I expect if I have a mental health disorder?

As mentioned, there is a range of symptoms that you may experience depending on which disorder is present. Even two people with the same disorder may experience different severity, frequency, duration of symptoms and even different symptom combinations altogether. While these symptoms may have far-reaching consequences in your life, it is possible to not realise you have one. If you are concerned, you should speak to a doctor about assessment

When should I see a doctor?

You should see a doctor if you are concerned about your mental health or if other people are concerned about your mental health. However, it is possible to suffer from a mental health condition unknowingly, so pay attention to the warning signs mentioned in the article, as these are causes for concern.


Mental health disorders encompass a wide range of conditions that significantly impact an individual's psychological well-being, health and overall satisfaction with life. Some of these disorders have shared core symptoms, and so can be categorised into the following disorders: mood, anxiety, psychotic, eating and personality disorders. 

Furthermore, they have shared underlying causes influenced by genetics and environmental factors, including certain risk factors. Recognizing the signs and symptoms early is crucial for identifying mental health conditions before they become entrenched. 

Assessment and diagnosis by trained professionals are essential for determining the specific condition and guiding treatment approaches. Management and treatment typically involve psychological interventions, medication, and, in severe cases, inpatient care. 

These disorders have profound consequences, leading to emotional suffering, substance abuse, family conflicts, impaired relationships, academic and employment difficulties, and increased mortality rates. By understanding mental health disorders and their implications, individuals can seek support and interventions in time to prevent harm before it is irreversible. 


  1. Sekhon S, Gupta V. Mood disorder. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2023 [cited 2023 Jul 19]. Available from: http://www.ncbi.nlm.nih.gov/books/NBK558911/
  2. Penninx BWJH, Pine DS, Holmes EA, Reif A. Anxiety disorders. Lancet [Internet]. 2021 Mar 6 [cited 2023 Jul 19];397(10277):914–27. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9248771/
  3. Calabrese J, Al Khalili Y. Psychosis. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2023 [cited 2023 Jul 19]. Available from: http://www.ncbi.nlm.nih.gov/books/NBK546579/
  4. Ekselius L. Personality disorder: a disease in disguise. Ups J Med Sci [Internet]. 2018 Dec [cited 2023 Jul 19];123(4):194–204. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6327594/
  5. Hirschfeld RMA. The comorbidity of major depression and anxiety disorders: recognition and management in primary care. Prim Care Companion J Clin Psychiatry [Internet]. 2001 [cited 2023 Jul 19];3(6):244–54. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC181193/
  6. Rihmer Z, Peter Dome P, Katona C. Serotonin and depression - a riposte to Moncrieff et al. (2022) [Internet]. U.S. National Library of Medicine; 2022 [cited 2023 Jul 19]. Available from: https://mppt.hu/magazin/pdf/vol24issue3/v24i3p120.pdf
  7. Karg K, Burmeister M, Shedden K, Sen S. The serotonin transporter promoter variant (5-httlpr), stress, and depression meta-analysis revisited: evidence of genetic moderation. Archives of General Psychiatry [Internet]. 2011 May 2 [cited 2023 Jul 19];68(5):444–54. Available from: https://doi.org/10.1001/archgenpsychiatry.2010.189 
  8. Tzouvara V, Kupdere P, Wilson K, Matthews L, Simpson A, Foye U. Adverse childhood experiences, mental health, and social functioning: A scoping review of the literature. Child Abuse & Neglect. 2023 Mar 10;139:106092. doi:10.1016/j.chiabu.2023.106092
  9. Global, regional, and national burden of 12 mental disorders in 204 countries and territories, 1990–2019: a systematic analysis for the Global Burden of Disease Study 2019. The Lancet Psychiatry [Internet]. 2022 Feb [cited 2023 Jul 19];9(2):137–50. Available from: https://linkinghub.elsevier.com/retrieve/pii/S2215036621003953
  10. Rihmer Z, Peter Dome P, Katona C. Serotonin and depression - a riposte to Moncrieff et al. (2022) [Internet]. U.S. National Library of Medicine; 2022 [cited 2023 Jul 19]. Available from: https://mppt.hu/magazin/pdf/vol24issue3/v24i3p120.pdf
  11. Tzouvara V, Kupdere P, Wilson K, Matthews L, Simpson A, Foye U. Adverse childhood experiences, mental health, and social functioning: A scoping review of the literature. Child Abuse & Neglect. 2023 Mar 10;139:106092. doi:10.1016/j.chiabu.2023.106092 
This content is purely informational and isn’t medical guidance. It shouldn’t replace professional medical counsel. Always consult your physician regarding treatment risks and benefits. See our editorial standards for more details.

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Finley Hansen

Bachelor of Science - BS, Neuroscience, Cardiff University / Prifysgol Caerdydd

Finley is a Neuroscience graduate with a culturally and practically diverse working background, with experiences in customer service, data analysis and research, healthcare, teaching and childcare. His roles have spanned the UK, India, Ghana and his current location in Thailand, where he works as a high school science and english teacher, online tutor and writer for Klarity Health.

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