“Hallucinations may be pleasant or scary. But what causes them? Colin Anderson Productions pty ltd/Getty Images
It may seem so real: that nasty smell of urine floating by, or the feeling of bugs crawling up your arm. The people around you aren’t experiencing it, which seems impossible. But actually, you’re experiencing a hallucination.
People who hallucinate typically see, hear, feel, smell or otherwise experience things that simply aren’t real. Sometimes, these sensory fake-outs are caused by something temporary or minor, but often, a pretty serious underlying medical factor is at play.
Even when the cause of a particular hallucination is often possible to pinpoint, scientists still struggle with understanding how the brain produces them. Recent strides were made when a 2019 study in mice discovered that hallucinogenic drugs cause activity in the visual cortex of the brain to slow way down, rather than speed up as was previously hypothesized. The researchers also found out that the visual cortex was receiving the same visual information that it would in absence of the drugs but was unable to interpret it correctly. This is a big deal because some mental health disorders, like schizophrenia, are strongly linked to the same receptors the researchers looked at, so a better understanding of how they work could someday produce more effective treatments.
Check out these common hallucinations to learn why they happen. If you’re experiencing any of them regularly, be sure to talk to a doctor.
1. Skin Crawling
Ever felt like bugs were crawling all over you, with nary an insect in sight? The feeling that your skin is crawling is a form of tactile (touch) hallucination. Another version is the sensation of movement within the body, like organs shifting around, or that something inside is trying to get out.
There are a couple of things that can cause a tactile hallucination. Certain medications that affect the central nervous system, as well as other meds that impact neurotransmitters, are associated with the unpleasant experience. Alcohol and drug abusers, particularly those who partake in cocaine or amphetamines, are also likely to have tactile hallucinations.
Medical conditions are also a serious culprit, with more than 50 percent of schizophrenia patients surveyed in 2016 reporting that they had experienced tactile or visual hallucinations. Neurological disorders like Alzheimer’s disease, Parkinson’s disease and Lewy body dementia also are connected with tactile hallucinations. People dealing with severe instances of such hallucinations are often directed to cognitive behavioral therapy to help them manage the emotional fallout.
2. Hearing Voices
People who hear sounds, such as voices, that aren’t actually there are dealing with auditory verbal hallucinations (AVH). Such voices can run the gamut from positive to negative and everywhere in between. Sometimes, the "voices" issue commands, but other times it’s just a constant commentary, often described as a "radio station in my head."
Seventy percent of people with schizophrenia report having AVH phenomenon. But AVH doesn’t only affect these patients. Those with bipolar disorder, some types of dementia, epilepsy, post-traumatic stress disorder and substance abusers are also at risk. AVH is actually more common than most people realize, and isn’t always associated with mental or other illness. In fact, it’s not uncommon for grieving people to hear the voices of recently departed loved ones. The reasons for AVH are unclear but scientists think it has to do with a disfunction among the frontotemporal regions of the brain. These are the regions of the brain involved with language, memory and emotional responses.
3. Smelling an Odor
Olfactory hallucinations (also called "phantosmia") occur when a person smells something that isn’t there. Most of the time, the odors are nasty, like feces, smoke, vomit or urine. Unfortunately, this usually happens when the olfactory system has sustained some sort of nerve damage, whether by trauma, virus, drug or toxin exposure or even brain tumors. Epilepsy is another known cause.
4. Seeing Lights or Beings
Visual hallucinations include seeing people, lights or patterns that no one else can spot. This is the most common type of hallucination for dementia patients, although people with delirium (disturbance of consciousness) also experience it. Once again, people with schizophrenia, dementia, drug abuse or Parkinson’s disease are also adversely affected (starting to see a pattern?)
Additionallly, people often report flashing lights and/or patterns during migraines, which is yet another way to experience a visual hallucination. This can also can occur during epileptic seizures. People who experience sleep disturbances, such as insomnia or narcolepsy, are also at added risk.
Visual hallucinations may be caused by a problem in a person’s brain structure, a malfunction of the brain’s neurotransmitters, traumatic past experiences or a combination of these. Whatever the cause, it’s important to figure it out, as treatment really depends on whatever is inspiring them to occur. If the wrong treatment is given, it’ll make things worse, not better.
5. Floating or Flying
This is called a proprioceptive hallucination, or a hallucination of posture. People who experience such an event report that they feel like they’re flying or floating, but sometimes like they’re in a whole different place from their actual body (known as an "out-of-body experience").
These experiences can be caused by sensory deprivation or overload, drugs (particularly hallucinogens) and even strong G-forces, like those that astronauts and pilots encounter. They can also spontaneously occur thanks to other factors, like extreme physical exertion, near-death experiences or sleeping lightly during times of stress, sickness or noise. Parkinson’s disease patients, in particular, are known to experience this type of hallucination.
6. Metallic Taste
People who experience a gustatory hallucination typically report an unpleasant, often metallic, taste in their mouth without any influence from food or drink. Although most people head to dental professionals for answers, these taste bud changes are rarely discoverable there, but are instead caused by things like head injury, virus, schizophrenia and systemic allergies.
A litany of medications can also account for this taste problem, including such commonly used options like aspirin, penicillin and Vitamin D.
Now That’s Sad
Research has shown that childhood trauma, whether it be bullying, neglect, emotional/physical/sexual abuse are linked to psychosis and hallucinations. In fact, people who experience severe sexual abuse as children are two to four times more likely to wind up with an adult psychosis diagnosis.