Formication

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Formication Classification and external resources
ICD-10	R20.2
ICD-9	782.0

Formication is an abnormal skin sensation similar to that of insects crawling over or within the skin. The word derives etymologically from the Latin word formica, meaning "ant". The causes of formication can be actual physical conditions, including diabetic neuropathy, menopause, skin cancer, or herpes zoster, and may also be physical or psychological side effect of substance abuse. Formication is a specific form of the general set of abnormal skin sensations known as paresthesia.

Formication is a common side-effect of the extensive use of cocaine or methamphetamine or the abusive use of amphetamines. Formication can also be experienced with high fevers. Extreme alcohol withdrawal may also cause symptoms of formication along with delirium tremens, often associated with visual hallucinations of insects. Formication is also a rare side effect of many prescription drugs such as Ritalin, Adderall and Lunesta.

People suffering from formication may scratch themselves to the extent of serious skin damage and bleeding, especially if they are delirious or intoxicated.

A related (or perhaps the same) condition is delusional parasitosis, where individuals believe there are bugs crawling under their skin. This may sometimes follow a case of scabies, since itching due to an allergic reaction to the remnants of parasites under the skin may persist after the parasites are eliminated.

Formication was neatly described in 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. It is probably due to the successive irritation of nerve fibrils in the skin. At times patients who suffer from it will scarcely be persuaded that it is not due to insects. Yielding to the temptation to scratch invariably makes the disease worse.^[1]

The term formication has been in use for several hundred years. In the 1797 edition of the Encyclopædia Britannica, a description of the condition raphania includes the symptom:

horrid convulsions of the limbs, preceded by a formication, or sensation as of ants or other small insects creeping on the parts.^[2]

The novel A Scanner Darkly by Philip K Dick (as well as the film of the same name) contains a scene where the character Charles Freck suffers from formication.

In the movie Old Boy, the main character experiences formication while imprisoned for 15 years.

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