Delusional parasitosis (DP) is a mental disorder in which individuals have a persistent belief that they are infested with living or nonliving pathogens such as parasites, insects, or bugs, when no such infestation is present. They usually report tactile hallucinations known as formication, a sensation resembling insects crawling on or under the skin. Morgellons is considered to be a self-diagnosed subtype of this condition, in which individuals have sores that they believe contain harmful fibers.


Delusional parasitosis is divided into primary, secondary functional and secondary organic groups.


In primary delusional parasitosis, the delusions comprise the entire disease entity, there is no additional deterioration of basic mental functioning or idiosyncratic thought processes. The parasitic delusions consist of a single delusional belief regarding some aspect of health. This is also referred to as “monosymptomatic hypochondriacal psychosis”, and sometimes as “true” delusional parasitosis. In the DSM-IV, this corresponds with “delusional disorder, somatic type”.

Secondary functional

Secondary functional delusional parasitosis occurs when the delusions are associated with a psychiatric condition such as schizophrenia or clinical depression.

Secondary organic

Secondary organic delusional parasitosis occurs when the state of the patient is caused by a medical illness or substance (medical or recreational) use. In the DSM-IV this corresponds with “psychotic disorder due to general medical condition”. Physical illnesses that can underlie secondary organic delusional parasitosis include: hypothyroidism, cancer, cerebrovascular disease, tuberculosis, neurological disorders, vitamin B12 deficiency, and diabetes mellitus. Any illness or medication for which formication is a symptom or side effect can become a trigger or underlying cause of delusional parasitosis.
Other physiological factors which can cause formication and thus can sometimes lead to this condition include: menopause (i.e. hormone withdrawal); allergies, and drug abuse, including but not limited to cocaine and methamphetamine (as in amphetamine psychosis). It appears that many of these physiological factors, as well as environmental factors such as airborne irritants, are capable of inducing a “crawling” sensation in otherwise healthy individuals, however some people become fixated on the sensation and its possible meaning, and this fixation may then develop into delusional parasitosis.

Who gets delusions of parasitosis and what is the cause?

The cause of delusions of parasitosis is unknown but it has been classified as a monosymptomatic hypochondriacal psychosis. This term is used to describe patients with a single fixed hypochondriacal delusion sustained over a considerable period but not secondary to another psychiatric illness. Apart from their delusions of parasitosis, patients may have an otherwise normal personality, or more commonly, an acceptable degree of eccentricity with a tendency towards social isolation.
Delusions of parasitosis have also been associated with other psychiatric illnesses including schizophrenia, obsessional states, depression, bipolar disorder and anxiety disorders. This is known as secondary delusions of parasitosis.
Delusions of parasitosis occur most commonly in white middle-aged or older women, although people of all races, sex and age can be affected.

What are the signs and symptoms of delusions of parasitosis?

People suffering from delusions of parasitosis often describe the infestation as being in or under the skin, just inside body openings or in sputum, inside their stomach or intestines, and in their surrounding habitat such as their bed, couch or throughout their home.

Characteristic symptoms of delusions of parasitosis include:

  • A patient seeking numerous opinions from medical doctors, exterminators, hygienist and entomologists, then often complaining about the incompetence of the advice received and treating the specialist with hostility and suspicion.
  • Sensations of itching, burning, crawling and biting that may lead to self-mutilation as the sufferer attempts to dig out the parasites. This causes minor scratches to gouged out pits and ulcers.
  • Exhibit the “matchbox sign” (also called “specimen sign”) which is where the sufferer offers for examination specimens kept in a small container such as a matchbox. Specimens usually consist of fragments of skin, hair, dried blood or scabs. Sometimes they may include living organisms such as ants or flies.
  • Extreme measures may have been taken to cleanse the skin and to disinfect or even destroy clothing and furniture.

How is the diagnosis of delusions of parasitosis made?

Complete physical examination and appropriate laboratory tests can help to identify other diseases that mimic the delusions of parasitosis and rule out any true infestations, e.g. with scabies or lice.

  • Skin scrapings and biopsies
  • Complete blood count
  • Chemistry profile
  • Thyroid function tests
  • Mineral and vitamin measurements, e.g. vitamin B12, ferritin (iron)

A history of drug abuse with cocaine, methylphenidate, or amphetamines must also be ascertained as these substances can induce the sensation of itchiness and result in skin picking.

What is the treatment for delusions of parasitosis?

The management of patients with delusions of parasitosis is often difficult as they are totally convinced of the existence and infestation of “their” parasites. Sometimes the disease may get better and go away on its own but in most cases, treatment with psychotropic medications is usually necessary. Often management of these patients is best handled through the cooperation of dermatologists, psychiatrists and entomologists. The following points should be taken into consideration when treating a patient.

  • Considerable tact and repeated visits are needed to gain the patient’s trust before broaching the actual existence of the infestation and noting that the problem is a psychiatric illness.
  • Do not “use the delusion” to encourage patients to accept certain treatments. For example getting a patient to take a psychotropic drug by telling them that this will “kill the parasites” only reinforces and validates their delusion.
  • Sufferers are often reluctant to seek psychiatric help, and if suggestions to do so by a doctor or dermatologist are not made carefully, the patient may not return for future visits.
  • Some patients may be able to live with their infestation without drug or psychiatric treatment by receiving appropriate reassurance, support and attention from their doctor or dermatologist.
  • Depressive symptoms should be screened for and treatment of depression may be useful. Escitalopram, a selective serotonin reuptake inhibitor, has been reported effective.
  • Antipsychotics such as pimozide, risperidone and olanzapine have all been used but should only be started under supervision from a dermatologist or psychiatrist.
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