Various different forms of hallucination exist, with some involving voices that can be heard and others involving non-existent smells or tastes. Hallucinations are a common symptom of schizophrenia but they can also be caused by drug abuse or excessive alcohol intake, fever, bereavement, depression or dementia.

Some of the different types of hallucinations that exist are described below:

Visual hallucinations

Here, a person sees something that does not exist or sees something that does exist but sees it incorrectly. Several conditions can cause visual hallucinations including dementia, migraines and drug or alcohol addiction.

Auditory hallucinations

This is the most common form of hallucination in schizophrenics and refers to the perception of non-existent sounds. In schizophrenia, patients often hear voices talking to them but the hallucinations may also take the form of whistling or hissing, for example. The voices may be saying complimentary, critical or neutral words to them. The voices may also form a running commentary on the person’s actions. Command hallucinations may also occur.

Auditory hallucination is also a well recognized feature of bipolar disorder and dementia, although they can occur in the absence of mental health conditions. Auditory hallucinations can be extremely distressing, although some people can learn to live with the voices, particularly if the words they hear are neutral or complimentary rather than negative. Auditory hallucination can also occur as a result of bereavement, which can lead to the person believing they can hear the voice of a loved one.

Olfactory hallucination

These hallucinations involve smelling odours that do not exist. The odours are usually unpleasant such as such as vomit, urine, feces, smoke or rotting flesh. This condition is also called phantosmia and can occur as a result of neurological damage in the olfactory system. The damage might be caused by a virus, trauma, a brain tumor or exposure to toxic substances or drugs. Phantosmia can also be caused by epilepsy.

Tactile hallucination

This refers to when a person senses that they are being touched when they are not. One of the most common complaints is the sensation of bugs crawling over the skin. This is associated with the abuse of substance such as cocaine or amphetamine.

Gustatory hallucination

These are hallucinations that cause a person to taste something that is not present.

General somatic hallucination

This refers to when a person experiences a feeling of their body being seriously hurt through mutilation or disembowelment, for example. Patients have also reported experiencing animals trying to invade their bodies, such as snakes crawling into their stomach.