Delusional parasitosis is a condition in which people firmly believe that they're infested by parasites, mites, worms or other organisms even though a physical examination by a healthcare professional doesn't support this idea. The condition also is called delusional infestation.

One form of delusional parasitosis is Morgellons disease. Symptoms of Morgellons disease include the feeling that fibers are emerging from the skin. People with this condition often report feeling as if something is crawling on or stinging their skin. The intense itching and sores that come with delusional infestation can severely interfere with quality of life.