There may be a number of factors which contribute to the development of 
symptoms of sensory overload/hypersensitivity. However, it may be difficult to specify which factors are contributing most to the development of symptoms. Potential contributory factors are detailed below:
- Attentional Difficulties: The person may struggle to attend to tasks (e.g. watching T.V., reading, talking, cooking, working, shopping) and find it difficult to screen out intrusive background stimuli in their environment (e.g. noise, activity, light). This means that the person is easily overwhelmed by particular sensory experiences thus affecting their ability to manage everyday tasks.
- Direct damage to the brain: e.g. neuropathic pain can result from damage to the thalamus, and allodynia (the experience of pain in response to light touch) can be associated with this. In Multiple Sclerosis people with brainstem damage have been reported to experience painful paraesthesia (abnormal sensation) in response to certain sounds. It is conceivable that similar processes could occur in people with brain lesions from other causes e.g. brain injury. It has been suggested that in some cases damage to efferent pathways (pathways which ‘dampen down’ sensory input) may contribute to sensory input which is not normally uncomfortable being experienced as painful/distressing.
- Damage to the sense organs themselves: this can cause unpleasant sensory experiences. Eye conditions which cause dry eyes can be associated with photophobia. Damage to the facial nerve can cause paralysis of the stapedius muscle in the middle ear. This muscle dampens down vibrations, protecting the inner ear from high noise levels. If it is paralysed, then normal sounds can be perceived as very loud.
- Causes unrelated or only partially related to brain injury: if a person experiences sudden onset of photophobia (sensitivity to light) or phonophobia (sensitivity to sound) then it is important to consider and exclude conditions such as meningitis. The most common cause of such symptoms is migraine which should be considered if these symptoms are reported. Post-traumatic migraine is a well recognised neurological sequelae of brain injury. Epileptic activity can also cause unusual sensory experiences.
- Other intracranial conditions may cause sensory symptoms which may present as overwhelm/sensory overload/hypersensitivity. Examples include subarachnoid haemorrhage, tumours, stroke and onset of neurodegenerative disorders.
- The consequences of hypervigilance: persistent over-attention to the environment in order to identify a potentially unpleasant stimulus (often
subconsciously), leading to avoidance behaviour. This may mean that they notice the ‘offending’ stimulus more when it is present. Consequently exposure to it may be even more uncomfortable. Avoiding exposure to the stimulus is likely to exacerbate this problem. If exposure to a particular stimulus is avoided (e.g. light, noise or touch) then the person is likely to become progressively more sensitive to it e.g. if you find light uncomfortable and wear sunglasses, over time you will find any exposure to light progressively uncomfortable through the inevitable process of ‘dark adaptation’. - May have a psychological basis e.g. arising from a Generalised Anxiety Disorder which may be associated with heightened levels of arousal in certain contexts e.g. noisy environments.
- May be related to the development of anticipatory anxiety e.g. a person who has previously experienced discomfort/pain during a particular intervention may subsequently become anxious and avoidant of the same intervention, a person who has feelings of overwhelm in particular environments (busy, noisy, brightly lit etc) may subsequently avoid these.
