What’s the Difference Between a Delusion and a Hallucination?

Delusions and hallucinations are similar but also have some significant differences. Both are often caused by the same mental illnesses, like schizophrenia or bipolar disorder; both involve distortions in reality; and both can occur even in the absence of mental illness.

The differences are that hallucinations are things that are sensed but not real, while delusions are beliefs that are not real or correct.

Both hallucinations and delusions are characteristic symptoms of psychosis and mental illnesses that can trigger psychotic episodes, such as schizophrenia. However, there are also other causes and triggers, including physical medical conditions. While one episode of a delusion or a single hallucination may not indicate any serious underlying condition, either one should be checked out and evaluated by a medical doctor or mental health professional.

A hallucination is anything that is sensed—heard, seen, felt, or even smelled—that is not real. The person experiencing a hallucination may believe that it is real, and everything about the vision, sound, voice, or other sensation seems very real.

The definition of delusion is a little different, although it also involves the experience of something that feels real but isn’t. A delusion is a belief that is obviously false, and yet the individual experiencing it thinks it is absolutely true. A delusion is not a belief that is false because of a person’s intelligence, education, culture, religion, or other similar factor; instead, it is false because it of some abnormality in the individual’s thinking. That person will firmly believe in the delusion even when repeatedly shown evidence to the contrary.

Both hallucinations and delusions are disturbances in reality. They are experiences that seem real to the observer but are not real. One difference is that a person experiencing a hallucination may realize it is not true—for instance, when a migraine causes an aura or lines in the vision. When caused by a mental illness, hallucinations and delusions often occur together.

Recent research has determined that as many as one in 20 people have hallucinations that are not caused by drug use, alcohol, dreams, or psychotic disorders. The study also found that about six percent of people have experienced hallucinations or delusions and that hallucinations are much more common.

A hallucination can literally be anything related to the senses, and different people with the same condition can experience something totally unique. There are some common types of hallucinations, though, including:

• A crawling feeling on the skin
• Hearing ordinary sounds that aren’t there, like doors closing or footsteps
• Hearing voices, including those that command a person to do something
• Seeing lights or patterns
• A sensation of floating or being outside one’s body
• Smelling an odor for which there is no explanation; this is rare

Any persistent and false belief may be a delusion, but as with hallucinations there are some common types and categories of delusions, most often triggered by a mental illness or psychotic episode:

• Persecutory. These are delusions in which a person believes someone is out to get them or is mistreating them.
• Grandiose. A grandiose delusion is any belief relating to having special powers, relationships with someone important or famous, or having exceptional talents or abilities.
• Jealous. Delusions of jealousy involve believing a partner is being unfaithful.
• Somatic. A false belief that one is sick or physically disabled is somatic.
• Bizarre. Delusions are often non-bizarre, meaning they could be true but aren’t. Bizarre delusions are those that could not be true, such as believing someone is controlling one’s mind.

There is evidence that perfectly healthy people sometimes experience hallucinations and less commonly delusions. However, if you have other symptoms, or these sensations or false beliefs persist, it is important to seek medical or mental health care. A doctor can rule out any medical conditions, while a mental health professional can screen for and diagnose an underlying mental illness. If there is a mental illness causing the symptoms, a thorough treatment plan that may involve medications and therapy can help.

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