They believe their skin is inhabited by, or under attack by, small insects or similar parasites, despite repeated reassurances from physicians, pest control experts, and entomologists.

Other causes are medical conditions such as pesticide exposure,[3] mercury poisoning, diabetic neuropathy, skin cancer, syphilis, Lyme disease, hypocalcaemia, or herpes zoster (shingles) and neurocysticercosis.

[citation needed] Formication is etymologically derived from the Latin word formica, meaning "ant", precisely because of this similarity in sensation to that of crawling insects.

In the 1797 edition of the Encyclopædia Britannica, a description of the condition raphania includes the symptom: ...a formication, or sensation as of ants or other small insects creeping on the parts.

[5]Described again in an instructional text from 1890: A variety of itching, often encountered in the eczema of elderly people, is formication; this is described as exactly like the crawling of myriads of animals over the skin.