Formication

# Overview
Formication is a somewhat unusual, but medically well-known, abnormal sensation. This sensation closely resembles the feeling of insects crawling on and/or under the skin, and can also include sensations which resemble those of insects stinging or biting. There are many known causes of formication.
The word is derived etymologically from the Latin word formica, meaning "ant", precisely because of this similarity in sensation to that of crawling insects.
Formication is a specific form of the general set of abnormal skin sensations known as paresthesia, and thus it is related to the sensation known as "pins and needles", and other tingling sensations.
Some people suffering the sensation of formication find it to be annoying, others find it painful, and some find it itchy. Those who find it to be itchy may in some cases repeatedly scratch themselves until they bleed, causing skin damage and sores. (In the subset of cases where the sufferer is delirious or intoxicated because of high fever, substance abuse, or extreme alcohol withdrawal, this repeated scratching is very common indeed.)
Formication can on occasion lead to people becoming fixated on the sensation and its possible meaning, and these people may develop delusional parasitosis. This is a situation where individuals are convinced that there are real insects crawling on and/or under their skin, whereas in reality there are no insects involved, just a crawling sensation. It is fairly easy to misunderstand the significance and causality of the "creepy crawly" sensation of formication.

# Causes
Formication is a somewhat unusual, but medically well-known, abnormal sensation. This sensation closely resembles the feeling of insects crawling on and/or under the skin, and can also include sensations which resemble those of insects stinging or biting. There are many known causes of formication.
The word is derived etymologically from the Latin word formica, meaning "ant", precisely because of this similarity in sensation to that of crawling insects.
Formication is a specific form of the general set of abnormal skin sensations known as paresthesia, and thus it is related to the sensation known as "pins and needles", and other tingling sensations.
Some people suffering the sensation of formication find it to be annoying, others find it painful, and some find it itchy. Those who find it to be itchy may in some cases repeatedly scratch themselves until they bleed, causing skin damage and sores. (In the subset of cases where the sufferer is delirious or intoxicated because of high fever, substance abuse, or extreme alcohol withdrawal, this repeated scratching is very common indeed.)
Formication can on occasion lead to people becoming fixated on the sensation and its possible meaning, and these people may develop delusional parasitosis. This is a situation where individuals are convinced that there are real insects crawling on and/or under their skin, whereas in reality there are no insects involved, just a crawling sensation. It is fairly easy to misunderstand the significance and causality of the "creepy crawly" sensation of formication.

## Life Threatening Causes
- Alcohol withdrawal
- Benzodiazepine withdrawal
- Carbon monoxide toxicity
- Cerebrovascular accident
- Cocaine intoxication
- Melanoma
- Mercury poisoning
- Methamphetamine intoxication
- Respiratory alkalosis

## Common Causes
- Adderall use
- Amifampridine
- Amiodarone
- Benzodiazepine withdrawal
- Causalgia
- Cerebrovascular accident
- Cocaine intoxication
- Colistimethate
- Compartment syndrome
- Delirium tremens
- Diabetic neuropathy
- Digoxin
- Dimercaprol
- Gopalan syndrome
- Guillain-barre syndrome
- Lanatoside c
- Lidocaine
- Lunesta
- Mefloquine
- Multiple sclerosis
- Notalgia paraesthetica
- Palifermin
- Peripheral neuropathy
- Posterior inferior cerebellar artery syndrome
- Riluzole
- Ritalin use
- Tetrodotoxin
- Thallium
- Thoracic outlet syndrome
- Topiramate
- Transverse myelitis

## Causes by Organ System

## Causes in Alphabetical Order
- 4-aminopyridine
- Adderall use
- Alcohol withdrawal
- Amifampridine
- Amiodarone
- Benzodiazepine withdrawal
- Carbon monoxide toxicity
- Carpal tunnel syndrome
- Causalgia
- Cerebrovascular accident
- Cocaine intoxication
- Colistimethate
- Compartment syndrome
- Delirium tremens
- Diabetic neuropathy
- Digoxin
- Dimercaprol
- Gopalan syndrome
- Guillain-barre syndrome
- Herpes zoster
- Hypocalcaemia
- Hypothyroidism
- Ito syndrome
- Lanatoside c
- Lepromatous leprosy
- Lidocaine
- Limb ischaemia
- Lunesta
- Lyme disease
- Mefloquine
- Melanoma
- Menopause
- Mercury poisoning
- Methamphetamine intoxication
- Multiple sclerosis
- Notalgia paraesthetica
- Opiate use
- Osteomalacia
- Palifermin
- Peripheral neuropathy
- Pesticide exposure
- Posterior inferior cerebellar artery syndrome
- Respiratory alkalosis
- Riluzole
- Ritalin use
- Syphilis
- Tetrodotoxin
- Thallium
- Thoracic outlet syndrome
- Topiramate
- Transverse myelitis
- Volkmann ischaemic contracture

# Referenced
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.
The term formication has been in use for several hundred years. In the 1797 edition of the Encyclopdia 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.

# Depictions of formication in fiction
- The novel A Scanner Darkly by Philip K Dick contains a scene where the character Jerry Fabin (and Charles Freck in the movie of the same name) suffers from formication and attempts to remedy the condition by showering for hours on end.
- In the movie Old Boy, the main character experiences formication while imprisoned for 15 years.