What Causes Hallucinations?

A hallucination is when someone senses something that it isn’t actually there. Instead, it is created by the mind. The three main types of hallucinations are visual, auditory hallucinations, and tactile (relating to touch) hallucinations, though some people can have olfactory (relating to smell) and gustatory (relating to taste) hallucinations.

Hallucinations have many different causes, including psychotic disorders like schizophrenia, medical conditions such as dementia, and substance abuse. Some people experience hallucinations in association with sleep deprivation or certain types of headaches.

Psychiatric Causes

A number of psychiatric conditions are known to cause hallucinations. For example, 60% to 80% of people with schizophrenia experience auditory hallucinations. They may also have visual hallucinations. These hallucinations tend to have a surrealist nature, involving severed bodies, random objects, or unidentifiable characters.

People with bipolar disorder can also experience hallucinations during a manic episode, as can individuals with psychotic depression. During a manic episode, where a person's mood is elevated, hallucinations may involve a voice that reinforces their upbeat mood.

In depressed individuals, their hallucinations are often related to their depressive feelings. Those with depression and tinnitus (ringing in the ears) may hear voices that reinforce negative self-talk and promote a further decline in mental well-being.

Vision or Hearing Loss Causes

Vision and hearing loss have also been associated with visual and auditory hallucinations. People with vision loss may see a phantom vision, which results from the brain adjusting to vision loss. In a person who lost their all of part of their eyesight, since visual data don't come through the eyes anymore, the brain fills the void and makes up images or recalls stored images for them to see. 

This condition is known as Charles Bonnet syndrome, which occurs in the absence of a mental condition. Moreover, it is most often happens in people with macular disease, retinal disease, neuropathic disease, or other eye diseases. The hallucinations may move or remain still, and they can appear in black and white or color. The length of the hallucinations can last seconds, minutes, or hours.

Similarly, people with hearing loss have been shown to experience auditory hallucinations, including voices, music, doorbells, and telephones. These hallucinations increase in severity as a person's hearing declines. Auditory hallucinations can be a precursor to hearing loss, so it’s important to talk to your healthcare provider if you experience these symptoms.

Other Medical Causes

A number of other medical conditions can contribute to hallucinations. For example, migraines can cause a person to see flashing lights, wavy lights, lightning bolts, or dots that obscure vision.

Similar visual hallucinations have also been associated with occipital seizures, which are seizures in the part of the brain that controls vision. They may be associated with nausea and headache, which makes it hard to distinguish them from migraine.

Post-traumatic stress disorder (PTSD) can also cause hallucinations of an auditory and visual nature. Combat veterans have reported hearing voices or cries for help. Trauma from experiencing childhood sexual abuse also elevates a person’s risk of having hallucinations. 

Research suggests that dementia, Parkinson’s, and Alzheimer’s are associated with hallucinations as well. In fact, visual hallucinations are predominant in brain diseases because they affect the part of the brain responsible for processing sensory experiences.

Fever, especially in children and older people, and severe illnesses like kidney failure, liver failure, HIV/AIDs, and brain cancer can also cause hallucinations.

Substance-Related Causes

Substance abuse can cause all forms of hallucinations. Psychoactive substances, also called psychedelics or hallucinogens, are a category of drugs that cause visual hallucinations.

They influence the way a person perceives the colors, shapes, and movement of objects in reality. Auditory hallucinations can occur as well. The ingestion of amphetamines can spark tactile hallucinations, where a person may feel bugs or other living objects crawling on and under their skin. 

In rare cases, drinking alcohol can also induce hallucinations. Alcoholic hallucinosis is a condition where people with severe alcohol dependence develop auditory hallucinations. These may occur during or after an episode of heavy drinking. These symptoms may remain after a person has stopped drinking and become sober.

Additionally, heavy drinkers who suddenly stop drinking alcohol may experience severe symptoms of alcohol withdrawal. These may have seizures, paranoia, and hallucinations, which can further contribute to confusion and irritability.