Hallucinations

Definition

A hallucination is a perception without a stimulus. The brain produces a sensory experience, a sound, a sight, a smell, a touch, that feels as real as anything genuinely present, but nothing in the outside world is causing it.

Hallucinations can involve any of the senses. Auditory hallucinations, such as hearing voices, are the most common kind in psychiatric conditions. There are also visual hallucinations, olfactory and gustatory ones affecting smell and taste, and tactile hallucinations, the sense of something on or in the body. Hallucinations are a symptom, not a diagnosis, and what matters is what's producing them.

Symptoms and key features

Hallucinations can involve:

• hearing voices or sounds that others don't hear, the most common type
• seeing things, lights, shapes, people, that aren't there
• smelling or tasting things with no source
• feeling sensations on or under the skin
• experiences that feel convincingly real, not imagined or pretend
• distress, fear, or confusion, especially when they're new or hard to make sense of

What it looks like

• You hear a voice clearly speaking to you when no one is in the room.
• You catch movement or a figure at the edge of vision that isn't there.
• You smell smoke or another scent that no one else notices and that has no source.
• You feel a touch, a crawling, or a pressure on your skin with nothing causing it.
• The experience feels real enough that it's genuinely hard to tell it apart from the world around you.

What people often confuse this with

Imagination or a vivid memory. Imagining a sound and hallucinating one feel different. Imagination stays recognizably internal and under some control. A hallucination is experienced as coming from the outside world, with the same realness as an actual perception.

Always a sign of serious mental illness. Hallucinations can be part of conditions like schizophrenia, but they have many other causes, including delirium, dementia, substance use or withdrawal, medical conditions, and severe sleep deprivation. Some hallucination-like experiences are common and not a sign of illness at all.

A reason to fear someone. Hearing voices or seeing things can be distressing for the person experiencing them. It doesn't make a person dangerous. People with hallucinations are far more often frightened and in need of support than a threat to anyone.

What research says

Hallucinations are well described across psychiatry and medicine. They're a core feature of schizophrenia and other psychotic disorders, can appear in mood disorders with psychotic features and in PTSD, and are common in delirium and dementia. They can also be caused by substance use and withdrawal, certain medical conditions, and severe sleep deprivation. The evidence is rated mixed because hallucinations are studied as a feature across many different conditions rather than as a single symptom with one unified literature.

Because the causes vary so widely, assessment matters. Some hallucinations, particularly new ones with confusion, can signal a medical emergency such as delirium, which needs urgent attention. Once the cause is clear, treatment follows from it, and can include treating an underlying illness, antipsychotic medication, and psychological approaches. Hallucinations are a symptom that can be understood and, in most cases, helped.