What causes mental ill health

Scientific and psychological research is taking place to try and determine what causes mental ill-health. Causes can be complex and a combination of variable factors such as genetics, brain and bodily function, occupational factors and life experiences.

Common factors that can affect mental health states  


Occupation-related factors

There are many areas or factors in the workplace that can cause or exacerbate mental ill-health. Work-related stress is one of those factors that can both lead to mental ill-health and be exacerbated by it.

Work-related stress can be caused by single events, a combination of events or a combination of other factors such as:

  • undue pressures (job demand)
  • poorly defined job roles
  • lack of control over work
  • unhealthy work–life balance
  • poor working relationships
  • organisational change
  • lack of variety in work
  • limited career.

Consequences of stress

The consequences of such causes can include:

  • poorer work performance
    • reduction in productivity and outputs
    • increase in human error rates
    • increases in the number of incidents and injuries
    • poor decisions
    • deterioration in planning and control of work
  • changes in workers’ values, attitudes and behaviours
    • lack of motivation
    • fatigue or mental burnout
    • poor timekeeping
    • worker changes to working relationships
    • hostility and conflicts between workers
    • poor relationships with clients
    • increases in disciplinary
  •  absenteeism
    • increases in sickness absence
    • general poor health and hygiene
    • increases in physiological conditions (eg sleeping issues, high blood pressure, body aches, heart disease).
    • presenteeism and leavism
    • psychological urge to attend work when not in a fit state to do so
    • financial and resource cost implications
    • reduction in productivity
    • lower morale.

Data on sickness absence, performance or worker retention rates can help to indicate possible causes, as can speaking with workers either face-to-face (one-to-one or in a group) or via surveys.

Biological agents

Microbial pathogens (such as viruses or bacteria) can influence the brain’s structure and function and be a causal factor during the development of mental ill-health. They can also exacerbate mental ill-health symptoms.

Pathogens can be contracted via the workplace. If a worker is experiencing mental ill-health symptoms, a pathogen (such as influenza) from another worker may be enough to alter their mental state and trigger more prolonged symptoms. This can lead to further mental ill-health symptoms and potentially a mental disorder. For example, bacteria such as Streptococcus can be causal factors in the development of obsessive-compulsive disorder (OCD).  A parasite infection known as Toxoplasma gondii may be connected to the development of schizophrenia.

Ionising radiation

Genetic mutations or cell destruction caused by radiation exposure can affect the structure, function and biological chemistry of the brain which can lead to mental ill-health.

For example, while radiation does not necessarily affect workers in all industries, air crews and astronauts are subjected to higher amounts of radiation via cosmic rays. These workers spend more time higher up in the Earth’s atmosphere where the radiation is greater. Organisations and OSH professionals operating in these industries must consider the possible mental ill-health consequences from radiation exposure.


Exposures to toxins can lead to acute or chronic mental ill-health. Different toxins may require different exposure levels before they have an effect (guidance should be sought, depending on the legislation of the country in which the organisation is located).

Metals – lead, aluminium, mercury, arsenic, thallium, manganese and tin are metals commonly associated with mental ill-health. Exposures can lead to depression, anxiety, memory loss, dementia, attention deficit hyperactivity disorder (ADHD) and insomnia. A well-known example of mental ill-health associated with a metal is mercury fumes which were inhaled in the tanning and hatting industry in the 18th and 19th centuries.

Mercury was used to process felt hats. Erratic behaviour, drooling, mood swings, erethism and dementia were experienced after the inhalation of mercury. This is where the phrase ‘as mad as a hatter’ derives from.

Gases – the brain can be deprived of oxygen when carbon monoxide, carbon dioxide or hydrogen sulphide are inhaled. The gases are known to cause mental ill-health symptoms. For example, survivors of carbon monoxide poisoning can experience developmental neurological or mental deterioration that can eventually lead to mental disorders such as depression or personality disorders. Inhaling carbon dioxide (CO2) can enhance  anxiety in those with panic disorder (PD) more than those with most other mental disorders.

Solvents – exposure to solvents such as ketones, glycols, aldehydes, alcohols and aromatic hydrocarbons can cause a range of mental ill-health symptoms. Solvent exposures can come from work activities or personal solvent use (via glues and aerosols).

Others – many other toxins have been shown to cause or exacerbate mental ill-health.

Traumatic events

Traumatic events are those that are significant enough to cause a heightened emotional and/ or physical response (stress processes) in the body. They are usually associated with loss, abuse, threats, isolation, injury and disaster and can have a negative impact on someone’s mental health. Traumatic events can also be experienced by observing, or learning about, an event (for example, listening to another’s experience and being affected by it).

Traumatic events can affect the brain by causing emotional injuries. Emotional memories are created deep in the brain and are stored (potentially indefinitely). Some memories do not dissipate easily (or at all) and can be recalled at any time. This triggers repeated stress responses in the body which can lead to continuous damaging effects (eg post-traumatic stress disorder, PTSD).

Experiencing a traumatic event can often cause shock which can eventually lead to denial, sadness, guilt or anger. If these feelings are continuous, they can lead to mental ill-health and symptoms such as:

  • flashbacks (reliving the traumatic experience in the mind)
  • emotional responses such as nightmares, sleep disturbances and numbing
  • addictive behaviour such as substance abuse
  • withdrawal from social interactions, work or generally becoming isolated
  • development of anti-social behaviour
  • confusion and/or impaired cognitive abilities
  • depression, anxiety or PTSD (developing into other mental disorders)
  • challenging thoughts of the person’s own mortality (which can lead to suicidal thoughts or behaviours).

Personal factors and lifestyle choices

Mental health can be affected by personal factors – either from a single factor (originating from one source) or a combination of different factors (from one or multiple sources). Wherever the source originates, symptoms may still be present or worsened while working.

Some examples of how a worker’s personal life can affect their occupational environment are:

  • financial hardship or debt
  • poverty or housing and transport issues
  • relationship issues (including caring responsibilities)
  • medical complications or illnesses
  • traumatic events (loss, grief, accidents, illnesses)
  • cultural, religious or spiritual beliefs
  • addictive behaviour (substance abuse, gambling, extensive social life)
  • life fulfilment
  • gender

Organisations should try to help workers to find a balance between their personal life and occupational responsibilities. Offering support or signposting workers to appropriate supportive mechanisms can help to prevent the development of mental ill-health.

Nutritional intake

As with all organs in the body, to remain healthy the brain requires different levels of amino acids, complex carbohydrates, essential fatty acids, minerals, vitamins and water. Although the link between nutrition and mental health is complex, it may also be an important factor regarding fuelling the brain with good nutrition can develop and support healthy neurotransmitter activity and protect the brain from oxidants that can have a negative  effect on mental ill-health symptoms.

Organisations and OSH professionals should recognise that there is a relationship between nutrition and mental health. This will help them to make informed decisions regarding the promotion of healthy eating and positive mental health.

Physical activity

The brain and body function collaboratively and have an effect on each other if there is damage or disease. Therefore, a lack of physical activity (ie, not increasing the heart rate above its resting state) can have negative consequences on mental health.

Organisations could encourage a culture that promotes physical activity. It is something that could be completed by workers on a regular basis (if possible) to help prevent, maintain or improve mental and physical health. Those who do usually feel more positive, alert, motivated and may be able to cope more positively with stressors than those who are less active.

Such activities could include:

  • walking, running or cycling
  • fitness classes or resistance training
  • sports (tennis, football, netball, swimming, basketball, martial arts, korfball and many others).


Poor sleep can negatively affect mental health. Conversely, mental ill-health can affect someone’s sleep.

Poor sleep or sleep disturbances can lead to:

  • depression, anxiety, general negative emotions, confusion, reduced motivation and irrational thought processes
  • feelings of isolation, loneliness, and social withdrawal
  • deficiencies with mental repair and recovery
  • episodes of mania, paranoia, psychosis and enhancement of any existing mental ill-health symptoms.

Mental ill-health can also affect sleep in a number of ways:

  • anxiety can enhance thought processes (that overtake lateral thinking and constructive thinking processes) and make it difficult to sleep
  • depression and seasonal affective disorder (SAD) can lead to oversleeping
  • severe depression with adverse associated thoughts that can lead to insomnia
  • post-traumatic stress disorder (PTSD) can lead to nightmares and night terror sleep disturbances (can also discourage someone from sleeping and lead to insomnia)
  • psychosis and paranoia-based thoughts, hallucinations and delusions can lead to someone feeling fearful to sleep due to disturbing thought processes
  • mania episodes can cause energetic thought processes and lead to someone feeling not tired (not wanting to sleep when their body requires it)
  • psychiatric medication can have side-effects such as insomnia, oversleeping or disturbed.

Female reproductive system

During the female menstrual cycle hormone levels can change quite dramatically. The change in hormones can cause one to experience different types of mild mental ill-health symptoms such as:

  • mood changes
  • sympathy
  • loneliness
  • anger
  • irritability
  • hopelessness and feeling overwhelmed
  • stress
  • anxiety
  • depression
  • fatigue or a lack of energy
  • concentration issues.

Symptoms may be experienced one or two weeks before the menstrual period begins or at some point every month. These can disappear after the menstrual period is completed. This is known as premenstrual syndrome (PMS).

Some can experience a more severe type of PMS called premenstrual dysphoric disorder (PMDD) where the symptoms are more intense or amplified and potentially devastating. Those with PMDD can experience severe depression and suicidal thoughts or tendencies which can be distressing.

The menopause is another stage of the female reproductive system development which occurs later in life. The body undergoes psychological and physical changes predominantly through a decrease in the hormone levels of oestrogen and progesterone. This can also lead to mental ill-health symptoms such as:

  • anxiety (through fear, isolation, frustration and irritability)
  • lower self-esteem
  • poor concentration levels
  • poorer judgement.

In some cases, the mental ill-health symptoms can lead to depression and suicidal thoughts or tendencies.