• Mental health disorders such as schizophrenia, bipolar disorder, or psychosis
• Central nervous system disorders
• Neurological disorders
• Toxic and metabolic disorders and conditions
• Sleep deprivation or disorders
• Physical disorders such as diseases of vision and hearing organs
• Drugs such as some medications, alcohol, and hallucinogens (e.g., plant hallucinogens)
• Stroke
• Post-traumatic stress disorder (PTSD)

More information on the different types of hallucinations and their causes are provided below.

1- How Do You Know If You Hallucinate?

If an individual is hearing, seeing, smelling, tasting, and feeling (touch) things that are not real or do not exist outside their mind, this individual is likely to be experiencing hallucinations.

2- Is It Normal to Hallucinate?

Hallucinations can be a sign of mental health, neurological, and physical disorders. They can also be a sign of drugs consumption such as alcohol and hallucinogens.

3- What Are the 5 Types of Hallucinations?

There are 5 types of hallucinations that are not all due to psychotic disorders. Hallucinations can be caused by psychiatric and physical disorders [1].

3.1. What Are Auditory Hallucinations?

An auditory hallucination is the perception of sounds that are not real or do not exist outside of the mind of an individual [2]. They can be due to the following causes:

• Schizophrenia

Schizophrenia is a complex and severe mental health disorder that is classified as a type of psychosis. It is characterized by significant alterations in thoughts, perception, mood, and behaviors [3].

• Central Nervous System (CNS) Disorders

These are disorders that affect the brain known as encephalopathies or the spinal cord which are known as myelopathies.

• Psychotic Depression

Psychotic depression is a major depression associated with symptoms such as delusions, hallucinations, sleep issues, reduced motivation, and the capacity to experience a pleasure. It is often associated with bipolar disorder and major depression.

• Mania

Mania is a mood disorder characterized by an excessive level of energy, arousal, and enthusiasm.

• Post-Traumatic Stress Disorder (PTSD)

PTSD is an anxiety disorder associated with extremely stressful or distressing situations.

• Peripheral Lesions

Peripheral lesions are lesions that affect sensory or motor neurons of the peripheral nervous system (outside the brain and the spinal cord).

• Middle and Inner Ear Diseases

There are many diseases that affect tissues and organs of the middle and inner ear causing dizziness, inflammation, discharge, or hearing loss.

• Auditory Nerve Disease

This disorder affects the auditory nerve responsible for transmitting sound to the brain.

• Stroke

Stroke is a condition characterized by a very low blood supply to the brain which prevents its proper function.

• Arterio-vascular malformations

These are malformations that affect arteries and vessels responsible for blood supply to organs involved in hearing.

• Delirium

Delirium is a state of mental confusion lasting hours or days with alterations in consciousness, cognition, and attention.

• Dissociative Identity Disorder

Dissociative identity disorder or multiple personality disorder is a mental disorder characterized by the presence of at least two states of personality.

• Pontine Lesions

These are lesions that affect the pons region of the brainstem part of the brain which controls hearing, balance, involuntary actions, taste, and facial sensations.

• Temporal Lobe Epilepsy

Temporal lobe epilepsy is seizures that began in the temporal lobe and spread to other areas of the brain.

• Hallucinogens

Hallucinogens are chemical substances that modify the function of the nervous system causing cognitive, behavioral, perception, and consciousness changes. The most known hallucinogen is LSD (D-Lysergic acid diethylamide).

• Alcohol Hallucinosis

Alcohol Hallucinosis is a chronic state of alcoholic intoxication that affects the auditory system causing hallucinations.

• Syncope

Syncope or fainting is associated with low blood pressure resulting in a loss of consciousness and muscle strength.

3.2. What Are Visual Hallucinations?

A visual hallucination is the perception of images that are not real or do not exist outside of the mind of an individual such as crawling insects or small animals [4]. They can be due to the following causes:

• Neurologic Disorders

Neurologic Disorders are diseases that affect the nervous system including the central nervous system (brain and spinal cord) and the peripheric nervous system.

• Epilepsy

Epilepsy is associated with seizures that are due to abnormal electrical activity in the brain.

• Migraine

A migraine is a severe form of headache that manifests as an excruciating pain on one side of the head accompanied by a feeling of sickness and an increased sensitivity to light and sound.

• Glaucoma

Glaucoma is due to an excessive increase in the intraocular pressure within the eye that leads to damages including vision loss.

• Optic Nerve Disorders

This disorder affects the optic nerves responsible for transmitting visual information to the brain.

• Toxic Metabolic Disorders

Toxic metabolic disorders are characterized by the accumulation of products of metabolism (metabolites) in the tissues of the body leading to their damage. When affecting the eyes, it can cause damages that lead to anomalies with vision, such as visual hallucinations.

• Toxic Metabolic Encephalopathy

Toxic metabolic encephalopathy is also associated with the accumulation of metabolites in the brain leading to damages. If damaging parts of the brain involved in vision, it can cause anomalies with the vision such as visual hallucinations

• Schizophrenia

Schizophrenia is a complex and severe mental health disorder that is classified as a type of psychosis. It is characterized by significant alterations in thoughts, perception, mood, and behaviors [3].

• Hallucinogens

Hallucinogens are chemical substances that modify the function of the nervous system causing cognitive, behavioral, perception, and consciousness changes. The most known hallucinogen is LSD (D-Lysergic acid diethylamide).

• Sleep deprivation

Sleep deprivation is associated with insufficient (not enough) sleep that can be acute or chronic leading to reduced alertness, performance, and health issues.

• Drug and Alcohol Withdrawal Syndromes

These withdrawal syndromes are due to the changes in neurotransmission mediated by GABA.

• Retinal Diseases

Retinal diseases are disorders that affect the retina of the eye such as macular degeneration, intraocular tumors, retinal tear, and macular edema [5].

• Affective Disorders

Affective disorders are mental conditions characterized by changes in mood and emotions such as major depressive disorder.

• Conversion Disorders

Conversion disorders are mental conditions that cannot be explained by the presence of a disease or injury and which are characterized by paralysis, blindness, or other symptoms of the nervous system [6].

• Cataract Formation

A cataract is the clouding of the lenses of the eyes that help focus on objects at different distances.

• Enucleation

Surgical removal of the entire eye from its socket.

• Narcolepsy

Narcolepsy is a chronic disorder associated with the reduction in the ability to regulate the sleep-wake cycles.

• Choroidal Disorder

The choroidal disorder is due to damages to blood vessels in the eye known as choroid causing anomalies in vision.

• Sensory Deprivation

Sensory deprivation is an intentional reduction in the perception of one or more senses.

• Intense Emotional Experiences

These are life experiences that had significant emotional effects on the affected individuals such as a loss of a loved one, sexual abuse, or traumatic experiences.

3.3. What Are Olfactory Hallucinations?

An olfactory hallucination is the perception of smell that is not real or does not exist outside of the mind of an individual [7]. They can occur with several mental health disorders such as:

• Schizophrenia

Schizophrenia is a complex and severe mental health disorder that is classified as a type of psychosis. It is characterized by significant alterations in thoughts, perception, mood, and behaviors [3].

• Bipolar Disorder

Bipolar Disorder is a mood disorder characterized by mood swings between periods of depression (depressive episodes), and elevated mood that can be severe known as mania (manic episode) or less severe known as hypomania.

• Substance Abuse

Abusive consumption of drugs

• Eating Disorders

Eating disorders are characterized by unusual habits of excessive eating (e.g., binge eating disorder) or insufficient eating (e.g., anorexia).

3.4. What Are Gustatory Hallucinations?

A gustatory hallucination is the perception of taste (often metallic taste) that is not real or does not exist outside of the mind of an individual [8].

• Temporal Lobe Diseases

Temporal Lobe Disease causes seizures that began in the temporal lobe and spread to other areas of the brain. They can be caused by tumors, injury to the head, stroke, brain infections, or brain lesions

• Parietal Operculum Lesions

These are lesions that affect a part of the cerebral cortex causing the absence of speech.

3.5. What Are Tactile Hallucinations?

A tactile hallucination is the perception of touch that is not real or does not exist outside of the mind of an individual [7]. They can be due to the following causes:

• Substance Abuse

Abusive consumption of drugs

• Drug and Alcohol Withdrawal Syndromes

These withdrawal syndromes are due to the changes in neurotransmission mediated by GABA.

4- Can Stress Cause Hallucinations?

Auditory hallucinations have been associated with Post-Traumatic Stress Disorder (PTSD). PTSD is an anxiety disorder associated with extremely stressful or distressing situations.

6- What Causes Hallucinations in the Elderly?

Most of the hallucinations in the elderly are visual or auditory which can be due to the following causes:

• Side effects of Medications
• Diseases such as brain cancer, kidney, or liver failure.
• Dementia and Alzheimer Disease
• Grieving
• Impairment in hearing and vision
• Delirium

Conclusion

Hallucinations are very complex and their treatment depends on the cause of the hallucination.

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