The 15 Types of Hallucinations (And Their Possible Causes)

One of the phenomena most associated with “madness” is hallucinations. That is, perceptions that do not correspond to reality and in which there is no stimulus present to trigger them (unlike illusions).

Hallucinations can appear as a symptom of a mental disorder, for example schizophrenia, or due to the consumption of psychoactive substances such as mushrooms or LSD. The most popular hallucinations are visual and auditory.

Hallucinations are perceptions that seem real but are created by the mind, occurring without an external stimulus. They can affect any of the five senses: sight, hearing, taste, smell, and touch. While hallucinations are often associated with mental health conditions like schizophrenia, they can also be triggered by substance use, medical conditions, sleep disorders, or stress. Understanding the different types of hallucinations and their possible causes can help individuals and healthcare providers identify underlying issues and seek appropriate treatment.

What Are Hallucinations?

Hallucinations are sensory experiences that appear real to the person experiencing them, but are not actually present in the environment. They can range from hearing voices to seeing people or objects that aren’t there. Hallucinations typically occur as a symptom of various mental health disorders, neurological conditions, or substance abuse.

It’s essential to distinguish between delusions (false beliefs) and hallucinations (false perceptions), as they are distinct but can sometimes occur together.

The exact nature of the different types of hallucinations is not entirely clear. However, it is known that people often experience hallucinations because some chemicals found in drugs influence synapses (the spaces through which neurons communicate with each other) and cause the activation of some brain regions, for example, the parietal lobe in the case of touch hallucinations.

Other times what triggers hallucinations is dysfunctional neurons that activate certain parts of the brain and have an effect on normal function. This last phenomenon occurs, for example, due to an excess of dopamine in the case of schizophrenia.

Now, experts assure that lack of sleep can also cause this phenomenon to occur. Since it has been proven that after 24 hours without sleep, a person is more susceptible to experiencing hallucinations. Likewise, spending a lot of time in situations of sensory deprivation can generate visions of elements that are not really there.

15 Types of Hallucinations and Their Causes

1. Auditory Hallucinations

Auditory hallucinations are perhaps the most commonly known and discussed type. They involve hearing sounds, voices, or music that do not exist. A person might hear a conversation, instructions, or even a single word or phrase repeated over and over again. These voices may be friendly or hostile, which can dramatically affect the person’s emotional state.

Possible Causes:

• Schizophrenia: Auditory hallucinations are a core symptom of schizophrenia, often leading individuals to feel persecuted or misunderstood.
• Bipolar disorder with psychosis: Hallucinations can appear during manic or depressive episodes.
• Stress or trauma: Extreme psychological stress or unresolved trauma can sometimes trigger auditory hallucinations.
• Sleep deprivation: Lack of sleep can cause the brain to malfunction, leading to auditory misperceptions.

2. Visual Hallucinations

Visual hallucinations involve seeing things that aren’t actually present. These could range from simple flashes of light to full, detailed images, such as seeing people, animals, or objects that no one else can see. The clarity of these hallucinations can vary — some are simple and fleeting, while others feel as real as anything in the physical world.

Possible Causes:

• Parkinson’s disease: Visual hallucinations are a common symptom as the brain’s ability to interpret visual information becomes impaired.
• Charles Bonnet syndrome: Those with severe visual impairments sometimes experience vivid visual hallucinations.
• Schizophrenia: Visual hallucinations are less common than auditory ones in schizophrenia but still prevalent.
• Delirium: Acute confusion caused by infection or medication can cause brief visual hallucinations.

3. Olfactory Hallucinations (Phantosmia)

Olfactory hallucinations involve the perception of smells that aren’t actually present. Often, these odors are unpleasant — like rotting food, smoke, or chemicals — but they can vary greatly from person to person. The smell may feel overpowering and can lead to significant distress.

Possible Causes:

• Temporal lobe epilepsy: Seizures originating in the temporal lobe can trigger olfactory hallucinations.
• Brain tumors: Tumors in certain areas of the brain, especially the frontal lobe, can affect the sense of smell.
• Parkinson’s disease: In addition to visual hallucinations, some individuals with Parkinson’s also experience phantosmia.
• Upper respiratory infections: An infection of the sinuses or nasal passages may cause distorted smell perception.

4. Gustatory Hallucinations

Gustatory hallucinations involve perceiving a taste that isn’t really there. Often described as unpleasant, the taste may be metallic, bitter, or foul. While rare, these hallucinations can disrupt daily life, leading to anxiety about eating or drinking.

Possible Causes:

• Epilepsy: Some individuals with epilepsy report experiencing unusual tastes before or during a seizure.
• Brain lesions: Damage to areas of the brain responsible for taste processing can lead to gustatory hallucinations.
• Chemotherapy: Some cancer treatments may alter a person’s sense of taste, causing persistent or occasional hallucinations.
• Medications: Certain drugs, particularly those affecting the central nervous system, can lead to gustatory hallucinations.

5. Tactile Hallucinations (Haptics)

Tactile hallucinations involve the sensation of physical contact that isn’t actually occurring. For example, someone might feel as though they are being touched or even that insects are crawling on their skin. These hallucinations can be distressing and may lead to excessive scratching or other behaviors to alleviate the perceived sensation.

Possible Causes:

• Cocaine or methamphetamine use: These stimulant drugs can lead to tactile hallucinations, often described as the sensation of bugs crawling on the skin.
• Alcohol withdrawal (delirium tremens): Severe withdrawal from alcohol can cause tactile hallucinations, along with visual and auditory disturbances.
• Schizophrenia: In some cases, tactile hallucinations occur alongside other types of hallucinations in individuals with schizophrenia.
• Neuropathies: Damage to nerves, such as in diabetes, can also result in distorted sensory experiences, including tactile hallucinations.

6. Somatic Hallucinations

Somatic hallucinations involve the perception of internal sensations, such as the feeling of one’s organs shifting, or the sensation of being invaded by foreign objects. Unlike tactile hallucinations, which involve external sensations, somatic hallucinations are internal and can be very disturbing.

Possible Causes:

• Psychotic disorders: Somatic hallucinations are often seen in schizophrenia and other psychotic conditions.
• Severe anxiety: Intense anxiety can lead to bizarre bodily sensations, including somatic hallucinations.
• Neurological damage: Brain lesions or certain neurological disorders can result in distorted internal bodily perceptions.

7. Kinesthetic Hallucinations

Kinesthetic hallucinations are related to the sense of movement. A person might feel like their body or limbs are moving in a way that isn’t actually happening. For example, they might feel as though their hands are clenched or that their legs are walking even though they are stationary.

Possible Causes:

• Parkinson’s disease: Movement-related hallucinations can occur as part of Parkinson’s disease, affecting both physical coordination and perception.
• Psychotic disorders: Some individuals with schizophrenia or bipolar disorder may experience kinesthetic hallucinations.
• Brain lesions: Damage to areas of the brain responsible for motor control can lead to abnormal perceptions of movement.

8. Hypnagogic Hallucinations

Hypnagogic hallucinations are those that occur just before falling asleep, as the mind transitions from wakefulness to sleep. These hallucinations can involve any sensory modality, but they are often visual or auditory. They may be vivid, bizarre, and sometimes even frightening.

Possible Causes:

• Sleep deprivation: A lack of sleep can lead to the brain misfiring during the transition to sleep.
• Narcolepsy: Individuals with narcolepsy often experience hypnagogic hallucinations as they drift off to sleep.
• Stress or anxiety: High levels of stress can interfere with sleep patterns, causing vivid dream-like hallucinations during the transition to sleep.

9. Hypnopompic Hallucinations

Similar to hypnagogic hallucinations, hypnopompic hallucinations occur upon waking. They can involve hearing voices, seeing figures, or feeling sensations as one transitions from sleep to wakefulness. These experiences can feel very real, leading to confusion or distress.

Possible Causes:

• Narcolepsy: Like hypnagogic hallucinations, these are common in narcolepsy, a condition where the brain’s sleep-wake cycle is disrupted.
• Insomnia: Chronic lack of restful sleep can cause disturbing wake-up hallucinations.
• Night terrors: People with night terrors or sleep disorders may experience hallucinations as they wake.

10. Command Hallucinations

Command hallucinations are a particularly dangerous type of auditory hallucination in which the individual hears voices giving commands. These commands might instruct the person to perform specific actions, which could range from harmless to dangerous.

Possible Causes:

• Schizophrenia: Command hallucinations are common in individuals with severe psychotic episodes.
• Bipolar disorder with psychosis: During manic episodes, some people may experience command hallucinations.
• Post-traumatic stress disorder (PTSD): Traumatic experiences may sometimes trigger command hallucinations, particularly involving violent or self-destructive behavior.

11. Peduncular Hallucinosis

Peduncular hallucinosis is a rare condition that causes vivid visual hallucinations due to damage in the brainstem. The hallucinations may be detailed, such as seeing figures, people, or objects, and often occur during the night or upon waking.

Possible Causes:

• Stroke: Damage to the brainstem caused by a stroke can lead to peduncular hallucinosis.
• Brainstem tumors: Tumors affecting the brainstem can result in vivid visual hallucinations.

12. Functional Hallucinations

These hallucinations are unusual because they occur in the presence of an actual stimulus. For example, a person may hear a voice while someone else is talking, but the voice they hear is distorted or different from what is actually being said.

Possible Causes:

• Schizophrenia: Functional hallucinations are often seen in schizophrenia, where real stimuli are misperceived.
• Auditory processing disorders: Issues with the brain’s ability to process sound can lead to functional hallucinations.

13. Reflex Hallucinations

Reflex hallucinations occur when one sensory stimulus triggers an incorrect perception in another sense. For example, seeing a flashing light may lead to hearing sounds, or tasting something may create an unusual smell.

Possible Causes:

• Epilepsy: Reflex hallucinations can result from seizures that affect multiple parts of the brain.
• Trauma: Brain injuries, particularly those involving sensory regions, can lead to reflex hallucinations.

14. Body Image Hallucinations

Body image hallucinations involve misperceptions of one’s own body. The individual may feel that they are distorted, or may believe parts of their body are changing in size or shape. This can be particularly disturbing, as it distorts their perception of themselves.

Possible Causes:

• Anorexia nervosa: People with anorexia may experience body image hallucinations, seeing themselves as larger than they are.
• Schizophrenia: Some individuals with schizophrenia may experience distorted body perceptions as part of their psychosis.

15. Cognitive Hallucinations

Cognitive hallucinations involve the perception of thoughts or memories that are not actually present. These can manifest as a sense of “remembering” an event that never occurred or as false memories being re-experienced.

Possible Causes:

• Dementia: Cognitive hallucinations are common in various forms of dementia, including Alzheimer’s disease.
• Trauma: Severe emotional trauma can lead to cognitive hallucinations, where the mind creates false memories to deal with past events.

Different modes of false perception

The so-called functional hallucinations are triggered by the presence of a stimulus that triggers another, this time hallucinatory, in the same sensory modality. This hallucination occurs, begins and ends at the same time as the stimulus that causes it. An example would be the perception of someone who perceives the tune of the news every time he hears the noise of traffic.

The same phenomenon occurs in reflex hallucination only this time the unreal perception occurs in a different sensory modality. This is the case that occurs in the example presented above.

The extracampine hallucination occurs in cases where the false perception occurs outside the individual’s perceptual field. That is, something is perceived beyond what could be perceived. An example is seeing someone behind a wall, with no other information that could lead one to think of their existence.

Another type of hallucination is the absence of perception of something that exists, called negative hallucination. However, in this case the behavior of the patients is not influenced as if they perceived that there is nothing, so that in many cases it has come to doubt that there is a true lack of perception. An example is the negative autoscopy in which the person does not perceive himself when looking in a mirror.

Finally, it is worth highlighting the existence of pseudohallucinations. These are perceptions with the same characteristics as hallucinations with the exception that the subject is aware that they are unreal elements.

Why does a hallucination occur?

We have been able to see some of the main modalities and types of hallucinations but, why do they occur?

Although there is no single explanation in this regard, various authors have tried to shed light on this type of phenomenon, some of the most accepted being those who consider that the subject who hallucinates mistakenly attributes his internal experiences to external factors.

An example of this is Slade and Bentall’s theory of metacognitive discrimination, according to which the hallucinatory phenomenon is based on the inability to distinguish real perception from imaginary perception. These authors consider that this capacity for distinction, which is created and is possible to modify through learning, may be due to excess activation due to stress, lack or excess of environmental stimulation, high suggestibility, the presence of expectations regarding what it will be perceived as, among other options.

Another example, focused on auditory hallucinations, is the Hoffman’s theory of subvocalization which indicates that these hallucinations are the subject’s perception of their own subvocal speech (that is, our internal voice) as something foreign to themselves (a theory that has generated therapies to treat auditory hallucinations with some effectiveness). However, Hoffman considered that this fact was not due to a lack of discrimination, but to the generation of involuntary internal discursive acts.

Thus, hallucinations are ways of “reading” reality incorrectly, as if there were elements that are really there even though our senses seem to indicate otherwise. However, in the case of hallucinations our sensory organs work perfectly, what changes is the way our brain processes information that arrives. Typically, this means that our memories mix with sensory data in an anomalous way, linking previously experienced visual stimuli to what is happening around us.

For example, this is what happens when we spend a lot of time in the dark or blindfolded so that our eyes do not register anything. The brain begins to invent things because of the anomaly of not receiving data through that sensory pathway while awake.

Hallucinations can be a complex and distressing experience, affecting individuals in various ways. Whether caused by mental health disorders, neurological conditions, substance use, or other factors, understanding the different types of hallucinations and their underlying causes is crucial for proper diagnosis and treatment. Seeking professional help is essential for managing and addressing hallucinations, as they can provide important insights into a person’s health and well-being.

FAQs About Hallucinations

What are the most common types of hallucinations?

The most common types are auditory and visual hallucinations, with auditory being more prevalent in conditions like schizophrenia.

Can hallucinations be a sign of a serious mental health condition?

Yes, hallucinations can be a symptom of serious mental health conditions, such as schizophrenia or bipolar disorder. However, they can also occur due to substance abuse or neurological conditions.

Can sleep deprivation cause hallucinations?

Yes, severe sleep deprivation can lead to visual and auditory hallucinations, as the brain starts to malfunction due to lack of rest.

What should I do if I experience hallucinations?

If you’re experiencing hallucinations, it’s important to seek medical advice. A mental health professional can help determine the cause and offer appropriate treatments.

Are hallucinations always related to mental illness?

No, hallucinations can also be caused by neurological disorders, drug use, or sleep disturbances, and are not always linked to mental illness.