What Causes Hallucinations?

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Hallucinations occur when a person experiences seeing, hearing, feeling, smelling, or tasting something that isn't really there.

The Diagnostic and Statistical Manual of Mental Disorders (DSM-5) classifies this phenomenon as one of the main symptoms of psychotic disorders. Hallucinations are commonly associated with schizophrenia. Around 60% to 70% of people with this condition experience these, with auditory hallucinations being the most common. 

Hallucinations may also occur in conditions such as post-traumatic stress disorder, personality disorders, or medical illnesses like eye disease and neurodegenerative conditions. This break from reality may result for a number of reasons.

This guide will examine the different causes of hallucinations in people and will cover the types, symptoms, and possible treatment methods for hallucinations.

Types of Hallucinations

A hallucination can involve any of the five senses. That means that perceptions can be felt through the ears, eyes, skin, nose, or tongue.

Auditory Hallucinations

These hallucinations occur when a person perceives sounds that are not actually present. In some studies, auditory hallucinations are observed in between 5% and 28% of the population.

Highly prevalent in schizophrenia, auditory hallucinations are also seen in 20% to 50% of people living with bipolar disorder. By some estimates, 10% of the population with major depression, and 40% managing PTSD also experience auditory perceptual disturbances. 

Auditory hallucinations may come in a variety of sounds. But when the non-apparent sounds are comprised of voices, they are referred to as auditory verbal hallucinations. 

Around 9% of children experience auditory hallucinations, with numbers that move between 5% and 16% in adolescence. When hallucinations are verbal, the voices may be degrading, commanding, or haunting enough to affect daily functioning. 

Visual Hallucinations

People who experience visual hallucinations will often see a non-existent image, believing it to be real. These incidents are more commonly observed in older people.

Visual hallucinations are commonly seen in degenerative diseases of the brain and eye. Patients with Parkinson’s disease may experience visual hallucinations, depending on how long the condition has lasted. The dopamine medication used to manage the disease also raises hallucination risk. Visual illusions may occur in up to 80% of Parkinson's patients over the course of their illness.

Dementias and eye/visual pathway diseases are also linked to visual hallucinations in patients. 

Tactile Hallucinations

Tactile hallucinations are also known as haptic hallucinations or tactile phantasmata. When a person goes through this experience, they usually feel touches to or under the skin in the absence of any real stimulation.

Tactile hallucinations can feel like pinpricks, the feeling of liquid or wind on the skin, a hand on the shoulder, etc. 

Somatic hallucinations are a variation of this condition. Here, sensations are felt inside the body without any corresponding stimuli.

Tactile hallucinations are generally rare in neurological and psychiatric conditions. However, one study found that these types of sensations make up the second-most common type of hallucination in the general population.

Olfactory and Taste Hallucinations

Hallucinations of smell are observed in a significant minor of patients with schizophrenia. Around 4% and 25% of individuals with the disorder experience these illusions. However, limited research exists on this phenomenon.

Olfactory hallucinations have been reported to occur in about 5% of the older population generally associated with an impaired sense of smell.

These hallucinations are otherwise known as phantosmia.They occur where odors are perceived without a source present. 

In addition to psychotic illnesses, phantosmia has been reported in the context of epileptic seizures, depression, migraines, and ear, nose, and throat diseases. 

The most commonly reported auditory hallucinations are burnt/smoky smells. Patients also report foul, unpleasant, spoiled, or rotten odors. 

Phantom smells can reduce the quality of life in patients. This condition has been described as intrusive and distressing. 

Olfactory hallucinations typically occur with taste or gustatory hallucinations. However, it is possible to experience these conditions independently.

What Causes Hallucinations?

Hallucinations are often the result of a psychotic disorder or a related condition. However, the exact mechanism behind these symptoms is less clear. There are a few possible explanations that have been proposed.

Auditory Hallucinations

Functional magnetic resonance imaging (fMRI) examinations have demonstrated how the spontaneous activation of the auditory network can contribute to hallucinations.

Likewise, a neurocognitive model called the VOICE model has proposed that an unbalanced limbic system mismatched against a hypoactive prefrontal inhibitory system is at play. 

The limbic system is a part of the brain responsible for processing emotions, memory, fear, pleasure, hunger, etc. When this system becomes hyperactive, and the brain's prefrontal region which is involved in cognitive control is unable to properly modulate this, hallucinations may occur.

Visual Hallucinations

There are different mechanisms intended to explain visual hallucinations in eye and brain conditions:

  • Perception Attentional Dysfunction: In this case, the body’s perception and attention networks are impaired, affecting visual processing. This visual dysfunction is associated with dementia or Parkinson’s disease.
  • Hyperexcitability: This model is tied to Charles Bonnet syndrome—a condition where visual hallucinations occur as the brain adjusts to vision loss. This can lead to increased spontaneous activity in parts of the brain associated with vision. In such cases, incidents of visual hallucination may be observed. 
  • Poor interpretation: This model proposes that the brain may be confused in its ability to attribute the source of internally generated sensations as internal.

Tactile Hallucinations

While tactile hallucinations can present as part of psychiatric illness, neurodegenerative diseases (such as Parkinson’s), illicit drug use, and medication may also cause hallucinations that feel like insects crawling on the skin, and other tactile sensations.

Olfactory and Taste (Gustatory) Hallucinations

Phantom smells may result from trauma or nasal conditions like sinusitis. Certain degenerative neurological conditions such as Parkinson’s disease and Alzheimer’s have links to olfactory hallucinations.

Viral infections can also cause damage to the olfactory receptor neurons (ORNs). The direct mechanism behind this remains unclear.

When experiencing phantom tastes—trauma, or infections of the upper respiratory tract may be responsible. Likewise, toxic substances and medicines can play a role in taste hallucinations. 

Treatment of Hallucinations

Hallucinations may be managed using different approaches. There are treatments to manage hallucinations and their impact.

Medication

Medication is the main approach to treat hallucinations in psychotic and other illnesses. Antipsychotics control many symptoms of psychosis such as anxiety, agitation, delusions, and hallucinations.

It’s important to note, however, that 25% to 30% of auditory hallucinations may offer resistance to antipsychotics.

Transcranial Magnetic Stimulation (TMS)

Repetitive TMS is a relatively new treatment option, and there is some data that it might be helpful in the management of hallucinations.

Psychoeducation

Education on the nature of hallucinations and mental illness can help individuals and their loved ones better manage these symptoms.

Psychoeducation also helps people learn about factors that influence the condition and how to better manage it. Psychoeducation is also a useful tool in managing the stigma around this disorder.

Cognitive Behavioral Therapy

For anyone managing hallucinations, cognitive behavioral therapy is another useful tool. This type of psychotherapy can help one challenge and change the way they think about and respond to these experiences.

A Word From Verywell

When reality is different from what your senses experience in real time, it can be incredibly challenging. Hallucinations may be the result of mental or physical conditions, and will often require active treatment. If you experience hallucinations in any form, it’s important to receive an accurate diagnosis from a healthcare provider. This diagnosis can form the basis of the appropriate management methods for the condition. 

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