Delusional parasitosis

Delusional parasitosis (DP) or delusional infestation is a mental disorder in which individuals have a persistent delusion that their body is infested with living or nonliving agents, such as parasites, insects, or bacteria, when no such infestation is present. People with this condition may have skin symptoms such as the urge to pick at one's skin (excoriation) or a sensation resembling insects crawling on or under the skin (formication), associated with tactile hallucinations. Morgellons disease is a self-diagnosed subtype of delusional parasitosis in which individuals falsely believe harmful fibers are coming out of their skin and causing wounds.

Delusional parasitosis is classified as a delusional disorder in the fifth revision of the Diagnostic and Statistical Manual of Mental Disorders (DSM-5). The precise cause is unknown, but is thought to be related to dysfunctional dopamine transmission in the brain similar to other psychotic disorders. Diagnosis requires the delusion—which cannot be explained by another medical condition—be the only symptom of psychosis and has lasted a month or longer. Few individuals with the condition willingly accept treatment because they do not recognize the illness as a delusion. Antipsychotic medications and and antidepressants can decrease symptoms.

The condition is rare and is observed twice as often in women as men. The average age of individuals affected by the disorder is 57. An alternative name, Ekbom's syndrome, honors the neurologist Karl-Axel Ekbom, who published seminal accounts of the disease in 1937 and 1938.