Delusional parasitosis is caused by changes in brain chemistry, specifically elevated dopamine levels in a region called the striatum, which disrupts how the brain processes physical sensations. In some people this happens on its own with no other underlying condition. In others, it’s triggered by drug use, medical illnesses, nutritional deficiencies, or other psychiatric disorders. Understanding which type is at play matters because treating the root cause, when one exists, is key to resolving the symptoms.
Primary vs. Secondary Forms
Delusional parasitosis comes in two distinct forms. In the primary form, the false belief of being infested with parasites is the only symptom. There’s no other psychiatric diagnosis, no substance use problem, and no underlying medical condition driving it. The delusion itself is the disease.
The secondary form is far more complex. Here, the delusion develops as a consequence of something else: a psychiatric illness like schizophrenia, depression, or dementia; a medical condition such as diabetes or thyroid disease; or substance use. Identifying which form a person has changes the entire approach to treatment, because in secondary cases the delusion often resolves when the underlying problem is addressed.
The Dopamine Connection
Both forms appear to share a common neurochemical thread. Researchers have proposed that the core problem is a malfunctioning dopamine transporter (DAT), a protein responsible for clearing dopamine from the spaces between brain cells in the striatum. When this transporter doesn’t work properly, dopamine builds up outside cells to abnormally high levels. The excess dopamine isn’t caused by the brain releasing too much of it. Instead, the recycling system that normally pulls it back into cells is sluggish or impaired.
This matters because dopamine plays a central role in how the brain assigns meaning to sensory input. When dopamine levels spike in the striatum, the brain can start interpreting ordinary skin sensations, a slight itch, a tingle, the feeling of a hair brushing against skin, as significant and threatening. Over time, the brain builds a narrative around those sensations: something must be crawling on or under the skin.
Structural Brain Changes
Brain imaging studies have found physical differences in the brains of people with delusional parasitosis. Compared to healthy controls, affected individuals show reduced gray matter volume in the frontal cortex (the brain’s decision-making and reality-checking center), as well as in striatal areas involved in processing sensation and reward. At the same time, they have increased white matter volume in regions that connect these areas, including parts of the frontal lobe and structures deep in the brain.
These findings support a model where the prefrontal cortex loses some of its ability to regulate and correct sensory signals coming from the body. In a healthy brain, the frontal regions act as a filter, evaluating whether a skin sensation is worth paying attention to. In delusional parasitosis, that filter is weakened, allowing false sensory signals to pass through unchecked and be interpreted as real infestations.
Drug and Substance Triggers
Stimulant drugs are the most commonly reported substance triggers, and the dopamine connection explains why. Cocaine and amphetamines both block the dopamine transporter directly, flooding the striatum with excess dopamine in essentially the same way that primary delusional parasitosis does, just through a different mechanism.
Cocaine is one of the most frequently documented causes. It blocks dopamine reuptake and also affects serotonin pathways involved in sensory perception. Amphetamines, including medications prescribed for ADHD, have been reported in multiple cases. All six amphetamine-related cases in one systematic review involved medications prescribed for attention-deficit hyperactivity disorder, not recreational use. Cannabis, methylphenidate, pemoline, and atomoxetine have also been linked to the condition, each through slightly different effects on dopamine or related brain chemicals.
Alcohol use and alcohol withdrawal are additional triggers. During withdrawal, the nervous system becomes hyperexcitable, which can produce intense crawling or tingling sensations on the skin and, in some individuals, full delusional beliefs about infestation.
Medical Conditions That Can Cause It
A wide range of physical illnesses can produce secondary delusional parasitosis, typically by affecting the brain or nervous system in ways that mimic the dopamine imbalance seen in primary cases.
Neurological conditions are among the most common medical triggers. Head trauma, strokes, multiple sclerosis, brain atrophy, encephalitis, meningitis, and complications from brain surgery have all been documented as root causes. These conditions can damage the prefrontal and striatal circuits that normally keep sensory processing in check.
Metabolic and endocrine disorders also play a role. Diabetes is a frequently cited cause, likely because diabetic neuropathy creates genuine abnormal skin sensations that, in vulnerable individuals, become incorporated into a delusional framework. Thyroid disorders, particularly hypothyroidism, can alter brain chemistry enough to trigger symptoms. Infections including HIV, leprosy, tuberculosis, and syphilis have been associated with the condition as well, possibly through their effects on the nervous system.
Nutritional deficiencies deserve special attention because they’re treatable and sometimes overlooked. Vitamin B12 and folate deficiencies are the two most common nutritional causes. Both vitamins are essential for healthy nerve function, and when levels drop low enough, they can produce neuropathy and altered brain chemistry that sets the stage for delusional beliefs about infestation.
Psychiatric Conditions as a Cause
When delusional parasitosis develops alongside another mental health condition, the other condition is considered the primary driver. Schizophrenia is one of the more common psychiatric causes, since it already involves disrupted dopamine signaling and a tendency toward fixed false beliefs. Depression, particularly severe depression in older adults, can also manifest with somatic delusions including beliefs about parasitic infestation. Dementia, anxiety disorders, and specific phobias have all been documented as underlying psychiatric causes.
Menopausal states appear in the medical literature as well, possibly because hormonal changes during menopause can affect both skin sensation and mood regulation simultaneously, creating a window of vulnerability.
Medication Side Effects
Certain prescription medications can trigger formication, the sensation of insects crawling on or under the skin, which in some individuals progresses to a full delusional belief. Documented culprits include topiramate (used for seizures and migraines), ciprofloxacin (an antibiotic), amantadine (used for Parkinson’s disease and influenza), corticosteroids, ketoconazole (an antifungal), and phenelzine (an older antidepressant). These medications affect the nervous system in different ways, but the common thread is their potential to alter sensory processing or dopamine-related pathways.
Who Is Most Affected
Delusional parasitosis is relatively rare but shows clear demographic patterns. It occurs more frequently in women than men and tends to appear in middle-aged and older adults. The condition often affects people who are otherwise socially isolated, which may reduce the social feedback that would normally challenge a delusional belief. In older adults, the combination of age-related brain changes, nutritional deficiencies, medication side effects, and chronic medical conditions creates overlapping risk factors that can make the condition particularly likely to develop.
One characteristic behavior is the “matchbox sign” or “specimen sign,” where individuals collect samples of what they believe to be parasites, often skin flakes, lint, scabs, or fibers, in small containers to present as evidence. This behavior is so common that clinicians consider it a hallmark of the condition.