Hallucinations are signs of mental illness, but they don’t always mean that a person is sick. They are, in fact, quite common.

A 2015 study done in Europe found that 7.3% of people said they had heard voices all their life. A study from South Africa on hallucinations in the general population estimated the higher rate at 12.7%

Scientists don’t fully understand why some people have hallucinations and others don’t. They don’t know what causes them in people with mental disorders such as schizophrenia.

Types of Hallucinations

Hallucinations are not always a sign of a mental health disorder. They can occur whenever there is a change in brain activity. 

Some people are more vulnerable to hallucinations when they fall asleep or partially wake up.

A 2019 study in mice that took a hallucinogenic drug found that the animals had less activity in brain regions that researchers have associated with processing incoming visual information.

This observation suggests that a hallucination could be the brain’s way of compensating for a drop in sensory information.

There are many types of hallucinations, including:

  • Auditory  : a person hears something that is not there, such as a voice or a radio.
  • Visual  : they cause someone to see something that is not real, such as a person or an animal.
  • Olfactory  : they can occur when a person smells something that is not there.
  • Gustatory : they transmit the taste to someone of something that he has not eaten.
  • Tactile  : they occur when a person has the impression that something or someone has touched them.
  • Somatic  : These hallucinations can affect the whole body, causing unreal sensations like that of insects crawling on the skin.

The causes

Many medical conditions and other factors can cause hallucinations. 


Medicines called hallucinogens can cause hallucinations. These drugs temporarily change the way the brain processes and sends information, causing unusual experiences and thoughts.

LSD, dimethyltryptamine (DMT) and certain mushrooms are common hallucinogens.


Schizophrenia is a mental illness that changes the way a person thinks and behaves. It can also cause psychosis, which is a loss of contact with reality.

People with psychosis may experience delusions and hallucinations and exhibit behaviors that are not typical. 

Antipsychotic medications can help manage symptoms, and some people do better with treatment.

Postpartum Mental Health Disorders

Many new parents struggle with   postpartum  depression and anxiety.

Some suffer from postpartum psychosis, but this is less common. For example, a mother thinks she hears her baby cry when the baby does not.

Since postpartum psychosis can put the baby at risk and disrupt the parent-child relationship, prompt treatment is essential. Therapy, medication, and social support can help.

Anxiety and depression

People with anxiety and depression may experience periodic hallucinations. They are usually very brief and often relate to the specific emotions felt by the person. For example, a depressed person may hallucinate that someone tells them that they are worthless.

Treatment of the underlying disorder can often eliminate these hallucinations.

Alcohol withdrawal

Alcohol withdrawal can cause hallucinations, especially in people who have a severe withdrawal syndrome called delirium tremens.

A person with delirium tremens may also become very sick, vomit, or shake. Symptoms often disappear after several days.

Dementia and other brain disorders

Dementia progressively damages the brain, including areas involved in sensory processing. People with mid-to-late stage dementia may experience auditory and visual hallucinations.

Occasionally they see dead people. In other cases, their hallucinations can be terrifying and can trigger feelings of paranoia and panic that prevent them from trusting caregivers.

Medications can help relieve these symptoms.


Sometimes hallucinations are a symptom of a seizure disorder. A person may experience hallucinations during or after a seizure which can be avoided by treating the seizures in most cases.


Some people with migraines have hallucinations during or just before a migraine. These hallucinations are frequently visual. A person may see spots and colors that are not there, or other unusual images.

Sleeping troubles

Some people have hallucinations that doctors associate with  sleep disturbances. Hallucinations usually appear when a person falls asleep or wakes up.

In some cases, the hallucination occurs with an episode of sleep paralysis, which occurs when a person wakes up and is temporarily unable to move.

Treating sleep disorders can help relieve symptoms. In some cases, knowing that the hallucinations occur because of brain changes during the sleep cycle can make them less scary.

Sensory disorders

People who are hard of hearing or visually impaired can experience hallucinations. This may be due to brain changes in the regions responsible for processing sensory, visual or auditory information.

Other causes

In some cases, hallucinations may not be related to disease or medication. For example, in some religious traditions, a person may report an auditory hallucination. A person sleeping in a house they believe is haunted may hear noises or see ghostly figures due to increased anxiety.

Hallucinations are not delusions

A hallucination is not a delusion, although the two are closely related. A delusion is a false belief, while a hallucination is a false perception.

Many people may have fallen in love with optical illusions and other mental tricks. However, a hallucination is more than an error of perception.

People with hallucinations see or hear things that aren’t actually there and don’t match the experiences of others around them.

They may also believe in the reality of their hallucinations or attach specific meaning and false beliefs to them. These attached false beliefs are illusions.

Other symptoms associated with hallucinations

Hallucinations often signal an underlying problem with how the brain processes information, such as when someone with dementia develops hallucinations or depression triggers psychosis.

Some other symptoms accompanying hallucinations include:

  • changes in brain function as a person ages
  • unusual beliefs
  • depression or anxiety
  • visual or hearing problems
  • paranoid or aggressive behavior
  • a belief in the existence of a conspiracy
  • an epileptic seizure
  • headaches