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Why Do People Experience Hallucinations?

Updated on November 16, 2012

Definition of hallucination

Why does the mind produce such extraordinary - and at times frightening - experiences called hallucinations? Do we fully understand exactly what they are or why the brain creates them? Rita Carter author of 'Mapping the Mind' talks about hallucinations as:

"exceptionally intense self-generated sensory experiences."

A further explanation is offered by the Free Dictionary:

Hallucinations are false or distorted sensory experiences that appear to be real perceptions. These sensory impressions are generated by the mind rather than by any external stimuli, and may be seen, heard, felt, and even smelled or tasted.

Hallucinations occur therefore without any stimulus that is identifiable and suggests that there may be an abnormality in perception.

There is a mechanism in the brain that helps to distinguish between conscious perception and internal memory-based perceptions. When something alters this mechanism or damages it, then hallucinations can occur. However, this is quite a simplistic view as it doesn't cover why people experience hallucinations or why different forms occur. So let's have a closer look firstly at the various category of hallucination.

Hallucinations can be familiar shapes and scenes or they can be bizarre and frightening.
Hallucinations can be familiar shapes and scenes or they can be bizarre and frightening. | Source

Definitions of similar words

Word Definitions
Illusion - the condition of being deceived by a false perception or belief.
Delusion - a false belief held strongly by the person despite invalidating evidence to the contrary. Normal stimuli are seen but are given a bizarre interpretation.Frequently a symptom of mental illness
Psychosis - severe mental disorder that involves derangement of personality and loss of contact with reality

What kind of hallucinations do people experience?

Hallucinations can manifest in many forms and affect various senses - either one or more at the same time. When more than one sense is affected simultaneously people then experience multi-sensory hallucinations.

The form that hallucinations take are related to - vision, hearing, touch, taste and smell. So basically a person experiencing hallucinations will be seeing, hearing, feeling, tasting or smelling something that is not there in the physical sense.

The list below does not cover all the variations of hallucination that can occur as this subject is vast, but shows the most commons forms:

Visual hallucinations

This is a false perception of sight and can involve various images such as shapes, figures, light flashes and colours. They can also be more complex in that people will see landscapes, animals or even bizarre situations. One of the most common forms, especially in mental health conditions, is a human like figure. In a number of cases these figures will take on religious or cultural form such as Jesus or the devil.

Auditory hallucinations

Auditory of course refers to hearing and are another common form of hallucination - also known as paracusia. The person experiencing auditory hallucinations often undergo a variety of manifestations:

  • Hearing voices is the most common type of auditory hallucination and is usually associated with mental health conditions such as schizophrenia. The person often describes one or more voices either inside or outside their head. The voices usually make comments about the person that are often uncomplimentary, even at times threatening. However, the voices heard can also be complimentary.
  • Exploding head syndrome - can also be associated with sleep disorders and some forms of epilepsy. People report very loud roaring, crashing, or various other noises within their heads. Although painless, the experience leaves people often distressed and frightened.
  • Musical ear syndrome - (MES) a variety of sounds may be heard such as music, singing, orchestras or even what seems to be broadcasters describing a game.

Smell (olfactory) Hallucinations

This is also referred to as olfactory hallucinations in relation to the olfactory system that is responsible for enabling us to interpret smells. Phantosmia is the medical name for smelling something that isn't physically present. Frequently hallucinatory smells are not pleasant and have been described as rotting fish, urine, faeces, vomit, dead bodies and smoke among others. People can also experience parosmia where a person is able to smell actual items but they do not have the usual scent that everyone else would associate with those specific things. Frequently the person is convinced that unpleasant smells emanate from their own body. These forms of hallucination are usually associated with medical disorders rather than mental health conditions.


These are hallucinations that involve touch or different feelings of sensory pressure on the skin or even the internal organs. This form of hallucination is often associated with drug abuse where the person feels as if 'things' are moving under their skin and is known as 'formication'.

General Somatic Sensations

These can be particularly distressing hallucinations. They often take the form of the person perceiving that their body is misshapen or in some way grossly abnormal. Examples are:

  • The person percieves their body being twisted or torn
  • Flesh falling off
  • Other kinds of mutilation.
  • It is also common with this form of hallucination for the person to feel that their body has been invaded by animals such as snakes, lizards, insects etc.


This is a false perception of taste and they are not normally pleasant tastes either. For example, many people who suffer from epilepsy will say that they have a constant taste of metal in their mouth. With this type of hallucination the person usually suffers from a medical disorder rather than a mental health complaint.

Hallucinations can be both a distressing and frightening experience.
Hallucinations can be both a distressing and frightening experience. | Source

What causes hallucinations?

There are a number of reasons that can lead to a person experiencing hallucinations. These can range from sensory deprivation to drug abuse and the hallucinations can take a certain form depending on what the cause is.

Why hallucinations are formed by the brain under certain circumstances is not fully understood. One of the major difficulties trying to research this condition is that hallucinations occur spontaneously and can be fleeting, making in depth study difficult. However, there are two broad schools of thought. Topological theory suggests that hallucination happens due to abnormal activity in specific areas of the brain. Hodological theory suggests that it is the pathways connecting various areas of the brain that are responsible.

In more basic terms, chemicals in the brain - for example dopamine and serotonin - that transmit signals from one brain cell (neurone) to another are imbalanced or are in the wrong area of the brain, so causing dysfunction. In addition, other researchers also believe that the signals themselves are either faulty or wrong, so causing abnormal functioning.

Continuing research is on-going. For example Dr Dominic Ffytche, Institute of Psychiatry, London, has developed a new method of studying hallucinations after they have been artificially induced. This unique method may give greater insight into why the brain produces hallucinations under certain circumstances.

Other theories on how or why hallucinations occur are split into several categories:

  • psychophysiologic- a disturbance in the structure of the brain
  • psychobiochemical - this suggest that the chemicals and neurotransmitters, due to disturbance are creating hallucinations.
  • psychodynamic - this theory suggests that hallucinations are due to the subconcious mind surfacing into consciousness.
  • psychological - many researches believe that psychological factors also play a part in the hallucination experience.

There are a bewildering amount of theories about hallucinations - perhaps reflecting the complexity of the human mind. It is very likely that hallucinations don't occur due to one factor but probably a combination of many.

There are also numerous medical conditions where hallucinations have been experienced. Below are the most familiar complaints, but the list is not exhaustive:

1. Mental health conditions:

The psychotic disorders such as Schizophrenia, schizo affective disorder, delusional disorder, paraphrenia all have hallucinations as one of the main symptoms. In addition people with Bi-polar Affective Disorder and major depression that develop psychotic episodes are also known to produce hallucinations. It is also possible for people who are extremely stressed and anxious to have mild auditory hallucinations. In addition, those who have suffered a recent bereavement may also have these experiences.

2. Medical conditions:

Ailments that affect the central nervous system can cause hallucinations. Examples are:

  • Brain Tumours, stroke, dementia.
  • Epilepsy.
  • Migraine.
  • Delerium tremens (D.T's) - a severe manifestation of alcohol withdrawal that has, as one of the many medical symptoms, visual hallucinations.
  • High fevers.
  • Amputation of a limb - this can produce a very distressing condition called 'Phantom Limb Syndrome', where the person can still feel sensations and even pain in the limb that is no longer there.
  • Hepatic encephalopathy - a condition of the liver where toxins build up affecting the brain.
  • Encephalitis - infection of the brain by the Herpes virus where taste and smell hallucinations are the most common.
  • Hyperthyroidism.
  • Severe fatigue/sleep deprivation.

3. Sensory deprivation:
In an environment where the usual external stimuli such as - light, sight, sounds, smells are significantly reduced or absent, hallucinations can occur. In addition, people who have experienced extensive periods of time isolated from others can also experience sensory deprivation leading to hallucination. Various experiments carried out in sensory deprivation on healthy people found that in many cases, after only 15 minutes of secluding the participants from sights, sounds and smells, hallucinations were generated.

4. Drug-induced:

It's not just illegal substances that cause hallucinations. Many prescribed medications can also have this distressing affect. At times the hallucinations experienced may be just a one off, but it can also be a symptom of drug-induced psychosis. Many of the hallucinations that are drug induced are often visual. People have reported seeing lights, colours and shapes that resemble animal or human figures. Some of their hallucinations are misperceptions. For example a coat on a hanger is seen as a person.

5. Hypnagogic & hypnopompic hallucinations:

These are hallucinations that can be visual, auditory or any other type occurring between the transition periods of waking to sleeping (hypnagogic) or from sleeping to waking (hypnopompic). They are usually of very short duration but on occasion can last longer. In many cases these hallucinations occur with people who suffer from narcolepsy which is excessive day time sleepiness. However, people who are healthy can also experience them.


Hallucinations are only a small part of what can happen within the brain. The reasons for hallucinations and why the brain should produce them under so many different circumstances is still a mystery. What we can be sure of is that if the enigma of hallucinations is solved, it will give one of the greatest insights into the working of the human brain - but it will also no doubt stimulate further puzzles.


Submit a Comment

  • Seeker7 profile imageAUTHOR

    Helen Murphy Howell 

    5 years ago from Fife, Scotland

    Hi Crystal Tatum, many thanks for stopping by and for leaving such an interesting comment. That was a terrifying experience to have especially when it happens with over the counter medicines! It is quite rare but maybe that makes it even scarier?

    Many thanks for the vote up - greatly appreciated!

  • Crystal Tatum profile image

    Crystal Tatum 

    5 years ago from Georgia

    You did a great job with this complex topic. I experienced hallucinations once, after using an over the counter medication for motion sickness. It was absolutely terrifying. Turns out, I'm one of the lucky few that had that reaction to that particular drug. Now I go with Dramamine and those acupressure bracelets and try to travel on an empty stomach! Voted up and interesting.

  • Seeker7 profile imageAUTHOR

    Helen Murphy Howell 

    5 years ago from Fife, Scotland

    Hi MT - lovely to hear from you - hope things are well with you!

    I agree, mental health problems of this magnitude must be terrifying indeed! I think as well, that it's not just the hallucanations these poor people have to cope with, but all the other symptoms in conjunction with them - I honestly wish they could find a cure for these mental health disorders, it is so distressing to see people going through what they do!

  • Seeker7 profile imageAUTHOR

    Helen Murphy Howell 

    5 years ago from Fife, Scotland

    Hi Graham, many thanks for stopping by always lovely to hear from you and glad that you enjoyed the hub!

  • Seeker7 profile imageAUTHOR

    Helen Murphy Howell 

    5 years ago from Fife, Scotland

    Hi Alastar, sorry for taking so long to reply back again - it's been one of those months when I'm constantly playing catch-up!

    What a horrific ordeal for that girl to go through! Do we know what led to her being possessed in the first place? I will have to listen to those tapes, I can believe that they are very creepy. That's very interesting as well about the photos - very scary stuff indeed!!

    I also agree with you, that when I had any paranormal experience I knew it for what it was and didn't have any of the oddness of an hallucination! To my mind, the theories that are banded about to account for the paranormal such as temporal lobe epilepsy, psychological stuff and all the rest fluffs over the facts. Besides all that, there must be a hell of a lot of people on the planet whose brains are definitely wired the wrong way to be suffering from all this epillepsy etc.. The fact is I don't buy it, the simplest and most probable cause, is paranormal.

  • Minnetonka Twin profile image

    Linda Rogers 

    5 years ago from Minnesota

    Helen-I commend you on this well written and informative hub on hallucinations. I have talked to many with hallucinations as someone in the mental health field. I have always felt grateful not to have a debilitating mental illness where hallucinations also accompany them. I feel so bad for someone that hears, see's or smells things that aren't there. How frightening!

  • old albion profile image

    Graham Lee 

    5 years ago from Lancashire. England.

    Hi Seeker. Thanks for yet another information packed hub. Your research shines through and your presentation is excellent. A very difficult subject indeed.

    Voted up and all.


  • Alastar Packer profile image

    Alastar Packer 

    5 years ago from North Carolina

    Once again we're on the same wave-length with a subject. And once again you've replied outstandingly. You're in a perfect position to see first hand that most people do indeed know the difference. My experience was a one time event and absolutely appeared, felt, and was heard as an outside of self entity- a very, very evil one at that. The Michael audios can be found on You-Tube and are some of, if not the most chilling listens anywhere to be found. The girl had already been through the psychiatric stuff and was being exorcised by two lay priests when they were made. Unfortunately she died. The case and tapes are well known. What isn't well known are a few photos that were taken that appeared to show anomalous entities around the tragic girl and that's not saying they were "demons.".

  • Seeker7 profile imageAUTHOR

    Helen Murphy Howell 

    5 years ago from Fife, Scotland

    Hi Gypsy, lovely to hear from you and glad that you found the hub interesting! To be honest I was a bit shocked at all the illnesses and other things that can cause hallucinations - it's a wonder we're not all going around seeing pink elephants and easter bunnies!!!

  • Seeker7 profile imageAUTHOR

    Helen Murphy Howell 

    5 years ago from Fife, Scotland

    Hi Alastar, lovely to hear from you and thank you for such a lovely comment - and as always a fascinating one.

    This poor girl Anneliese Michael, now I don't know all that much about this case and this poor soul but from what you've described it doesn't sound like she was getting the help that she really needed. The thing is if that poor lass was tormented by demons, but was being helped by people who just don't buy into anything paranormal then no matter what treatment they threw at her, it wasn't going to work! As we know already, hallucinations can be triggered by all manner of things, but most of the people I've spoken to or patients that I looked after, who had experienced them, knew that they were hallucinations. No one that I've spoken to for example had an hallucination about their dead mum standing at the foot of the bed, neither did they believe that they were having a paranormal experience. So the point is, there is a difference. I think also paranormal visitations - whether in dreams or within the physical - seem to present and feel different that the experience of hallucintion. In addition, as you have already mentioned, audio tapes can caputure disembodied voices, sometimes along with physical evidence on film, so no one can claim that this is to do with psychology or bodily functions? The fact is, is that the term hallucination is used to mean and cover anything that doesn't fall within a textbook! Because the exact origins of hallucinations are not known, then it's easy for some to lump the paranormal into this category as well, without looking at the facts properly.

    The subconcious is fascinating. There are quite a few theories that maintain the sub-conscious is an indirect path through for spirits, others believe that the sub-conscious is a direct route. What I do believe is that spirit works through the mind and not through the brain, therefore the spirit faces that poor Anneliese saw might well have been the real thing - especially with the voices as well. The subCon is such a deep maze things certainly could be lurking there, as you rightly say 'so deep within' but it's also possible that other energies hide there?

    Alastar as always, many thanks for your wonderful insights and support - greatly appreciated!!

  • Gypsy Rose Lee profile image

    Gypsy Rose Lee 

    5 years ago from Riga, Latvia

    Voted up and interesting. Thanks you for this informative hub. I thought most hallucinations happened to people under the effect of narcotics or wandering in the desert. This was a great read. Passing this on.

  • Alastar Packer profile image

    Alastar Packer 

    5 years ago from North Carolina

    Helen, you've managed to condense into article length- and done so superbly- what it often takes others 200+ pages to do in a book. I'd like to mention the tragic case of Anneliese Michael. Its know from the contention of the experts that the poor girl was just suffering from a dissociated personality disorder. I've studied her case and have even experienced what she called demon faces. Now, to me, those tapes that were made during the exorcism are either coming from a place so deep down within us its still a mystery, or something from outside the girl used her. Tha'ts my take and I stand on it. Hallucinations don't belong wholly to the insane. You point out in the story all the other many things they can be linked to. Ja some say all manifestations can be explained psychologically and biologically. Maybe most can, but I believe we shouldn't close the door on other possibilities yet. Great topic Helen. Up n Awe

  • Seeker7 profile imageAUTHOR

    Helen Murphy Howell 

    5 years ago from Fife, Scotland

    LOL!!! Hi kashmir56 - you've made laugh with your wonderful comment! It's interesting though that when I was researching for it, there seemed to be an awful lot of people who have hallucinated due to various causes - I wondered then if reading too much about it might produce hallucinations!! Happily that didn't happen but it must be a horrible experience to have!!

  • kashmir56 profile image

    Thomas Silvia 

    5 years ago from Massachusetts

    Hi my friend i found this hub very interesting and informative . And reading it produced no hallucinations or after effects .

    Well done and vote up and more !!!

  • Seeker7 profile imageAUTHOR

    Helen Murphy Howell 

    5 years ago from Fife, Scotland

    Hi Frank - many thanks for visiting and thank you for the lovely comment!! Glad that you found the mysteries of the brain interesting!!

  • Frank Atanacio profile image

    Frank Atanacio 

    5 years ago from Shelton

    seeker what a very interesting and I should add informative and entertaining hub.. wow...


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