Delusional Parasitosis

Delusional parasitosis, is a delusional disorder in which individuals incorrectly believe they are infested with parasites, insects, or bugs, whereas in reality no such infestation is present. Individuals with delusional parasitosis usually report tactile hallucinations known as formication, a sensation resembling insects crawling on or under the skin.
The cause may be physical, physiological, psychological or combinations of these factors.