Symptom perception refers to a conscious awareness of a symptom following unconscious information processing. Sensation refers to a bodily perception. A symptom reflects a negatively valenced interpretation of a sensation. A bodily complaint is the expression of a symptom.

Bodily signs are objective and verifiable. Illness symptoms are interpretation signs. Bodily complaints are subjective and self-reported.

Somatisation refers to the inclination to worry about somatic symptoms. In the general population, 20% experiences a somatic symptom that causes some level of worry at least once a month. Almost 20% - 50% of the symptoms reported to the GP remain medically unexplained (e.g. fatigue, impaired sleep, pain). People are not good at interpreting their physical state accurately.

There are four groups that exhibit distinct patterns of symptom reporting:

1. Regular people
   This includes a high number of mundane symptoms. In times of increased stress and reasons to worry, an inclination develops for heightened attention towards their symptoms leading to increased medical consumption.
2. Patients with a verified disease
   This is similar to regular people but there is a heightened vigilance for illness-specific symptoms and increased attribution to illness.
3. Patients with medically unexplained symptoms (MUS)
   This includes all previous characteristics but is limited to a more-or-less unified cluster of symptoms defining a syndrome.
4. Somatisation disorder patients
   This includes all previous characteristics combining into multiple clusters of symptoms.

Somatic symptom disorder involves a person having a significant focus on physical symptoms that results in major distress and/or problems functioning. There are excessive thoughts, feelings and behaviours related to the physical symptoms. Illness anxiety disorder refers to excessively worrying that one is or may become seriously ill. There might be no physical symptoms.

There are different psychological factors that influence the perception and interpretation of symptoms:

1. Attention
   The degree of attention to the internal physical state has a strong influence on the perception of symptoms.
2. Environment
   The environment influences symptom perception (e.g. distracting environments lead to less symptom perception).
3. Individual differences
   There are individual differences in the degree to which people pay attention to internal states and which symptoms they are more likely to attend to. This is influenced by schemas (1), past experience (2), perceived cause of the symptoms (3) and attributional style (4).  
4. Emotion
   The emotional state of a person influences attention to (1), appraisal (2) and interpretation of symptoms (3).

Negative emotions are associated with an increased report of symptoms and associating symptoms with illness more often. Anxiety makes people hypervigilant and sensitive to threat. Misperception of symptoms leads to a delay in seeking help (1), overuse or underuse of healthcare services (2) and compromised treatment (3). This demonstrates the importance of education about symptom recognition.

Pathology and normal physiological variation provide somatic information. This can lead to symptom perception. There are several things that determine the attention and symptom perception:

1. Nature of signs (e.g. new sign; persistence; linked to a pre-existing disease).
2. Signs that are perceptually intrusive (i.e. visible).
3. Signs that have little distraction (i.e. competition of cues).
4. Negative affect and personality (i.e. attentional an interpretation biases).
5. Experience, knowledge and expectations.

The competition of cues model states that people report more symptoms when they are less distracted. Trait and state negative affect are associated with elevated symptom reporting. People who complain about psychological symptoms are also more likely to complain about physical symptoms. A higher expectancy of symptoms leads to more symptoms.

There is elevated symptom reporting and fatigue during exercise when confronted with own physiological response (e.g. breathing). The experienced shortness of breath after exercise in patients is determined by illness-specific perceptual-feedback (e.g. wheezing) but not by actual lung capacity.

Pain refers to a distressing experience that is associated with actual or potential tissue damage. It occurs in a social context and has different aspects to it. Nociception refers to the stimulation of peripheral pain receptors which sends messages to the central nervous system. Suffering refers to the perceived pain, distress and disability that can arise from pain and related factors.

Pain threshold refers to the point at which a stimulus becomes painful. This is similar for most people. Pain tolerance refers to the degree to which a painful stimulus can be tolerated. This varies widely between individuals. Acute pain refers to pain which is necessary to protect us from damage or infection. Chronic pain can lead to changes to the neural pathway of pain leading to the perception of pain even when there is no physical injury. The effects of chronic pain can be prevented by early intervention.

The gate theory of pain states that there is a synaptic gate between peripheral nerves and neurons in the spinal cord. Pain signals compete with other signals to get through the gate and the gate can be opened or closed by physical and psychological factors. This theory states that stimulating another body part during pain can reduce the perceived pain. The neuromatrix model of pain states that pain is the result of interacting neural networks with somatosensory, limbic and cognitive components.

Conditioning approaches focus on the role of operant conditioning in behavioural responses to pain. Cognitive-behavioural approaches focus on behavioural factors (e.g. operant conditioning) and individual factors (e.g. perceived pain). The fear-avoidance model states that when people catastrophize about pain, there is greater fear of pain (1), greater focus on pain (2) and restricted functioning (3). The functional-contextual approach focuses on processes and function of thoughts and behaviours rather than the content. This approach focuses on psychological flexibility and treatment is focused on improving functioning.

The communal coping model (CCM) looks at the relationship between pain and catastrophizing thoughts and behaviours. According to the model, some people are predisposed to deal with distress by catastrophizing. This is thought to communicate distress and is an attempt to increase social proximity and support from others. The social function of catastrophizing is the most important.

The placebo effect refers to improving due to the expectancy of improving. This effect is more powerful for conditions with psychological components and not effective for conditions with a clear biological basis (e.g. infections). The nocebo effect refers to people developing symptoms that fit their beliefs when they have not been exposed to a pathogen. Classical conditioning is important in the placebo and nocebo effect, meaning that the presentation of medication is important.

Illness representation refers to people’s organized sets of beliefs about the experience (1), impact (2), effect (3) and outcome of illness (4). The dimensions of illness representations are illness identity (1), timeline (2), cause (3), control (4) and consequences (5).

The self-regulation model of illness behaviour states that illness representations can affect the way a person copes with their symptoms. This means that people are less likely to adhere to treatment for an illness without symptoms. Self-management interventions refer to interventions which target a person’s beliefs and coping to help them manage their illness and treatment effectively.

There are gender differences in chronic conditions and disease and symptom reporting:

• Women report more symptoms.
• Women more often seek primary medical consultation.
• Women are more often referred to specialist care.
• Women use more and wider variety of prescribed medication.
• Men have a lower life expectancy.

The medically unexplained symptoms and gender-specific symptoms are only a minor component of gender differences. Having multiple roles (e.g. work, family, children) has a protective effect.

The competition of cues model may explain part of the gender differences (e.g. women are more often in jobs that require repetitive labour). Negative affect could also explain part of the gender differences as women rate higher on negative affect and neuroticism. Women generally have a larger vocabulary regarding symptoms and more knowledge about disease, which could explain part of the gender differences. Biological explanations for gender differences in symptom reporting and disease include sensory differences (1), immune differences (2) and larger physiological variance (3).

Medically unexplained symptoms or functional symptoms refers to diagnosis based on self-reported symptoms with no diagnostic physiological test. The diagnosis is based on exclusion and there is no disease-specific treatment available. It is possible that differentiation between specific functional syndromes reflects the specialist’s tendency to focus on symptoms relevant to their speciality.

Functional symptoms are common, persistent and associated with significant distress (1), disability (2) and unnecessary expenditure of medical resources (3). The prevalence of emotional distress and disorders in patients who attend hospital with functional syndromes is higher than patients with comparable medical conditions.

It has substantial clinical and economic impact as it is disabling (1), there is high comorbidity with psychological disorders and elevated stress levels (2) and there is high medical consumption and costs (3).

There are several important points about functional syndromes:

1. Various syndromes strongly overlap in symptom profile.
2. People often meet diagnostic criteria for multiple functional syndromes.
3. There are shared risk- and predictive factors between the functional syndromes.
4. The same treatments appear to be effective for all functional syndromes.

The medical protocol regarding functional syndromes consists of discouraging medical testing (1) and emphasising recovery rather than cure (2). It appears as if antidepressants and psychotherapy are effective in the treatment of functional syndromes.

The number of functional complaints is related to past episodes of anxiety and depression. There is a link between functional somatic syndromes and altered functioning of the central nervous system. Dissatisfaction with medical care is common among patients with functional syndromes.

Functional symptoms are more common in women (1), people with a low socio-economic status (2) and people with a history of child abuse (2).