Delusions of Parasitosis

Updated: Jul 18, 2018
Author: Bettina E Bernstein, DO; Chief Editor: Glen L Xiong, MD 



Delusions of parasitosis (DoP) manifest in the patient's firm belief that he or she has pruritus due to an infestation with insects. Patients may present with clothing lint, pieces of skin, or other debris contained in plastic wrap, on adhesive tape, or in matchboxes. They typically state that these contain the parasites; however, these collections have no insects or parasites. This presentation is called the matchbox sign, or what the authors term the "Saran-wrap sign."

The patients have no obvious cognitive impairment, and abnormal organic factors are absent. True infestations and primary systemic diseases that cause pruritus are not involved. Primary skin lesions are not present. Physical examination may reveal no lesions, but only linear erosions with crusts, prurigo nodularis, and/or ulcers.

The classification of delusions of parasitosis is complicated. It is considered primarily a monosymptomatic hypochondriacal psychosis and has been associated with schizophrenia, obsessional states, bipolar disorder, depression, and anxiety disorders. Delusions of parasitosis occur primarily in white middle-aged or older women, although the condition has been reported in all age groups and in men.

Savely et al[1] introduced the term Morgellon disease to describe a condition characterized by fibers attached to the skin. The entity appears to be little more than a new designation for delusions of parasitosis. Koblenzer[2] and Waddell and Burke[3] have discussed the utility of the term, with Murase et al[4] finding the term useful for building a therapeutic alliance with patients with delusions of parasitosis. The Centers for Disease Control and Prevention is currently investigating Morgellon disease.[5]

William Harvey[6] of the Morgellons Research Foundation Medical Advisory Board states the following:

"All patients with Morgellons carry elevated laboratory proinflammatory markers, elevated insulin levels, and verifiable serologic evidence of 3 bacterial pathogens. They also show easily found physical markers such as peripheral neuropathy, delayed capillary refill, abnormal Romberg’s sign, decreased body temperature, and tachycardia. Most importantly they will improve, and most recover on antibiotics directed at the above pathogens."

The author of this article has not found reliable data to back up William Harvey's claims, but they are included here to comprehensively address this issue.[7]

Walling and Swick[8] suggest abandoning 3 the diagnostic terms trichotillomania, delusions of parasitosis, and neurotic excoriation, which they believe have become barriers to treatment. Instead, they suggest using the alternative patient-centered nomenclature of neuromechanical alopecia, pseudoparasitic dysesthesia, and (simply) excoriation.

It is important to note that many patients with psychopathology complain of delusions of parasitosis, but the coexistence of delusions of parasitosis and another condition, the author thinks, is independent of pure delusions of parasitosis without other symptoms.[9, 10]

One study of 47 patients reported that those noting bugs appeared to be more likely to be diagnosed with of delusional disorder or to have a medical diagnosis, as opposed to those noting fibers, who were more likely deemed to possess a somatoform disorder. Patients referred to a medical setting for delusions of parasitosis were 300 times more likely to require a physician to engage the hospital's legal counsel versus other patients in the same clinical setting.[11]

European researchers reported a series of 148 delusions of parasitosis patients. None of the patients possessed genuine infestation, as was shown by thorough examinations. Thirty-five percent of the patients believed themselves to be parasite infested. Most patients in this series noted a significant number of other living or inanimate (17%) pathogenic agents. Seventy-one (48%) of the 148 patients presented to doctors with “proof” of their infestations. These specimens were, for the most part, skin bits or hair and rarely insects. Only a few of these insects were anthropophilic or of human pathogenicity. No insects could be linked to the clinical presentations.[12]

Two comprehensive reviews in 2013 reiterated the necessity for clinicians to establish a therapeutic alliance with patients due to the challenges of treating a condition that a clinician might think is psychological in nature while the patient is convinced it is real and physical.[13, 14]

To help the patient a strong theraputic alliance must be established with the patient.[15]


The cause of delusions of parasitosis is unknown. It appears related to neurochemical pathology. This concept is underlined by its induction by psychoactive agents (eg, amphetamines, cocaine, and methylphenidate) and its coincidence with depression, schizophrenia, social isolation, and sensory impairment. Some reports have linked delusions of parasitosis to hyperthyroidism, which was deemed a secondary type of delusions of parasitosis, because it resolved with pimozide therapy and thyroid medications.



The exact prevalence of delusions of parasitosis is unknown.


The literature includes one report of suicide in a 40-year-old man with delusions of parasitosis.[16]

Race-, sex-, and age-related demographics

Delusions of parasitosis appear to be more common in whites than in people of other races.

Delusions of parasitosis occur primarily in white middle-aged or older women, although the condition has been reported in all age groups and in men. The female-to-male ratio is approximately 2:1. More specifically, this ratio is 1:1 in people younger than 50 years and 3:1 in those older than 50 years.[17, 18]





Patients must be queried about their symptoms, the duration of symptoms, and their belief about the etiology. Notably, Goddard[19] has described a seasonality to delusions of parasitosis, and Vila-Rodriguez et al discuss the facilitation of delusions of parasitosis resulting from Internet-based dissemination of the condition.[20]

The diagnosis and treatment of delusions of parasitosis (DoP) can be an involved clinical activity. Patients with DoP can resist suggestions that their condition is psychiatric rather than physical and refuse referrals for psychiatric care. In fact, in 35% of patients, the belief of infestation is unshakable.[21] In approximately 12% of patients, the delusion of infestation is shared by a significant other. This phenomenon is known as folie à deux (eg, craziness for 2) or folie partagé (ie, shared delusions). Variations in this are the conviction that a child, a spouse, or a pet is infested.

The condition of DoP is a monosymptomatic psychosis, a type of psychopathology relatively distinct from the remainder of the personality. If the condition has a defined pathologic or external cause (eg, scabies), it is not truly delusions of parasitosis. In investigating the history of a patient with such suspected delusions, other causes of itch must be investigated. To diagnose this condition, true infestations (eg, scabies), pediculosis, and primary systemic causes of pruritus must be excluded.[22] Examples include hepatitis, HIV infection, dermatitis herpetiformis, thyroid disease, anemia, renal dysfunction, neurologic dysfunction, and lymphoma.

Delusions of parasitosis are distinct from formication. Formication involves the cutaneous sensation of crawling, biting, and stinging. Formication does not involve the fixed conception that skin sensations are induced by parasites. Patients with this condition can accept proof that they do not have an infestation. Many cases of formication remain idiopathic.

The diagnosis of DoP should be made carefully. Iatrogenic delusional parasitosis, a case of physician-patient folie a deux, has been noted in which a physician made the diagnosis of delusions of parasitosis that was then carried in the medical record, although the patient in fact did not have DoP or actual infestation.[23]

Delusions of parasitosis can occur in isolation on the eyelids, which can result in blindness.[24]  It can also present as a belief that the patient has a disseminated fungal infestation. Authors estimated that 1% of patients with DoP may believed that they are infected with fungi.[25]  

Mimics of delusions of parasitosis

Other forms of psychiatric illness can mimic delusions of parasitosis. Such psychiatric illnesses are accompanied by signs of mental illness. Delusional parasitosis can be the presenting feature of dementia, in which case the delusions of parasitosis is actually secondary.

For example, patients with schizophrenia may think they are being attacked by insects as a manifestation of their paranoia.

A type of severe depression termed psychotic depression may cause the patient to believe he or she is contaminated or "dirty" because of insect infestation. Such a patient may have a depressed mood and a sense of helplessness, hopelessness, worthlessness, or excessive guilt. Often, these feelings are obvious at clinical presentation.[26]

Drug-induced delusions of parasitosis have been reported during treatment for Parkinson disease.[27] Gabapentin-induced delusions of parasitosis has been noted.[28]

Steinert and Studemund[29] reported a 45-year-old man who did not have a history of psychological pathology, who, after ingesting ciprofloxacin to treat an infection, was overcome with acute delusional parasitosis. He stopped taking the ciprofloxacin, and the delusions of parasitosis resolved altogether without utilization of an antipsychotic agent. Tran et al reported a patient who had delusions of parasitosis after receiving a therapeutic dose of mefloquine,[30] and Krauseneck and Soyka reported an association of delusions of parasitosis with pemoline drug therapy.[31]

Cases in which an etiology is defined are best classified as secondary delusions of parasitosis.

Guarneri et al[32] noted a patient who was thought to have delusions of parasitosis but who, in fact, had infestation with Limothrips cerealium; they termed the condition pseudo-delusory syndrome (ie, infestation with an uncommon insect).

Ghaffari-Nejad and Toofani[33] noted a case of secondary delusions of parasitosis in a patient with major depressive disorder who had delusions of oral parasitosis; the patient sensed lizards and small organisms in her mouth.[34]


Patients with delusions of parasitosis create their rash. They can present with no findings, erosions or ulcers with or without crusts or prurigo nodularis. They may evidence a dermatitis related to attempted treatments, which may include irritating or corrosive cleansers or harsh abrasive devices. Delusions of parasitosis involving the eyelids has been reported.[35]



Diagnostic Considerations

Other conditions to consider include the following:

  • Alzheimer's dementia
  • Recreational use/abuse of drugs (e.g., cocaine, stimulants, narcotics)
  • Side effects of therapeutic drugs such as anti-Parkinsonian agents, stimulants, antidepressants, antihypertensives, antiepileptics


Differential Diagnoses



Laboratory Studies

No laboratory test can help in diagnosing delusions of parasitosis; however, laboratory tests can help identify other diseases that can mimic delusions of parasitosis. Note the following:

  • To exclude infestation, a mineral oil preparation should be used to eliminate scabies, and a microscopic examination of skin and hair should be performed to exclude louse infestation.

  • Neurologic pathology due to toxins or vitamin deficiencies can be evaluated with the appropriate tests.

  • Tests to assess other causes of pruritus (eg, low iron level, liver or kidney disease) can be performed if clinically indicated. Examples include evaluation of the complete blood cell count; urinalysis; liver function tests; thyroid function tests; and determinations of levels of serum electrolytes and glucose, blood urea nitrogen, serum creatinine, serum vitamin B-12, folate, and iron.

  • Unless dermatitis herpetiformis needs to be excluded, skin biopsy is usually more useful to reassure patients of the lack of pathology than to diagnose delusions of parasitosis.

  • Use of cocaine, methylphenidate, or amphetamines must be ascertained, and if occurring, it should be stopped.

  • It is useful to examine the "proof" that the patient brings in so that one may truthfully say that the material was examined and no parasites were found. One authority anecdotally relates how he found ants in the debris and, after explaining that these arthropods did not live on or in humans, was able to give practical advice to reduce the problem.

Imaging Studies

Huber et al found striatal lesions in patients with secondary delusions of parasitosis, but not in cases of primary delusions of parasitosis.[36] In rare cases, neurologic impairment (eg, tumors, neuritis, multiple sclerosis) can mimic the symptoms of delusions of parasitosis. Causes of such impairment should be excluded with MRI or CT scanning if they are strongly suspected on the basis of the clinical findings.

Histologic Findings

Delusions of parasitosis have no specific histologic findings. All skin changes are secondary to rubbing, scratching, picking, or other treatment attempts.

Because patients who have delusions of parasitosis are having delusions, performing biopsies on them is not useful because any finding, even if negative for parasites, will not affect the delusion.[37]



Medical Care

In 2014, an article on delusions of parasitosis stressed the need of the physician to establish a therapeutic alliance with patients suffering from the condition. Without this alliance it is difficult to convince patients to take the necessary medications. The first meeting with a patient with DP can set the tone for all subsequent encounters.[38]

Another article states that the patient's autonomy must be respected in all encounters.

The physician must provide provide full information regarding the treatment plan and seek consent before starting treatment or asking the patient to seek a psychiatric referral.[39]

There has been an increase in combined psychiatric/dermatologic approaches to treating delusions of parasitosis, using a multidisciplinary approach with dermatologists working with psychiatrists and others. One clinic in Singapore used this approach and noted that delusions of parasitosis was the most common psychophysiologic disorder. The study noted that 20% of patients had psychiatric disorders underlying their skin problems and that trichotillomania and dermatitis artefacta were also observed.[12]

The only clear method to clear the delusion that underlies delusions of parasitosis is the administration of psychotropic medications. However, the condition can remit on its own. If the sensation of itch is related to some actual disease or substance use rather than a monosymptomatic hypochondriacal psychosis, the disease can be treated, or the substance inducing the sensation can be eliminated.

It is vitally important that the practitioner does not "use the delusion" to encourage the patient to accept certain treatments. While getting the patient to take a medication, such as risperidone, may help the condition, telling them that it is a medication that "kills the parasites" reinforces and validates the delusion. Even giving the patient a course of topical permethrin "just in case" may strengthen the delusion and make it that much more difficult later on. Every delusions of parasitosis patient can recount the visit on which his or her suspicions of infestation were "confirmed."

Serotonergic antidepressants may have a role in the treatment of these patients.[40, 41]

Reichenberg et al[42] reported on a patient whose delusions of parasitosis was cured overnight by having him stop taking cetirizine and doxepin (25 mg), as well as any over-the-counter medications.

Rocha and Hara[43] reported that aripiprazole at 15 mg for 8 weeks and then 7.5 mg/d was effective for delusions of parasitosis treatment. They stated:

Aripiprazole has a unique pharmacologic profile that is different from other atypical antipsychotic drugs. It is considered a partial dopaminergic agonist acting on both postsynaptic dopamine D2 receptors and presynaptic autoreceptors. It acts as a weak stimulator (so-called “partial” agonist) at dopamine D2 receptors, with the potential for exerting either antagonistic (inhibitory) or agonistic (stimulating) effects, depending on the sensitivity of the receptors and availability of dopamine, its natural agonist in the brain. In addition, aripiprazole displays partial agonism at serotonin (1A) receptors and antagonism at serotonin (2A) receptors.

Secondary delusional parasitosis was treated successfully with the combination of citalopram and clozapine. What relevance this has for treating primary delusions of parasitosis is unclear. A middle-aged woman treated with extended-release mixed amphetamine salts developed secondary delusions of parasitosis, which resolved with stopping the medication, underlying the need to assess medication usage before making a diagnosis of delusions of parasitosis.

Ladizinski et al also report that aripiprazole may be a useful treatment for delusions of parasitosis.[44]

Szepietowski et al[45] sent out 172 specially designed questionnaires to dermatologists regarding delusions of parasitosis patients; 118 responded. The questions and resulting percentages are as follows:

  • Had seen at least one patient with delusions of parasitosis - 84.7%

  • Had 1-2 cases of delusions of parasitosis over the preceding 5 years - 33%

  • Had seen 3-5 such patients over the preceding 5 years - 28%

  • Had diagnosed no cases of delusions of parasitosis during the past 5 years - 23%

  • Had more than 10 patients with delusions of parasitosis over the past 5 years - 7%

  • Were currently treating a patient with delusions of parasitosis - 20%

  • Always request a psychiatric opinion about their patients with delusions of parasitosis - 40.75%

  • Often ask for a psychiatric opinion about their patients with delusions of parasitosis - 28.8%

  • Use their own pharmacological treatment, mostly sedatives and anxiety-relieving drugs - 15.3%.


A psychiatrist should be consulted if the dermatologist cannot or will not prescribe the necessary medications. Most patients with delusions of parasitosis are reluctant to see a psychiatrist, and the dermatologist may be more successful in giving the referral if they have gained the patient's trust after several clinic visits instead of immediately after meeting the patient.



Medication Summary

The current treatment of choice is risperidone[46, 47] or olanzapine.[48, 49, 50] The older treatment of choice is pimozide.[51] Several more recent articles have suggested other psychiatric medications can be used to treat delusions of parasitosis, including escitalopram (Lexapro, Forest Pharmaceuticals; New York, NY)[10, 52] and aripiprazole.[53]

The most common adverse effects of pimozide are extrapyramidal symptoms, including stiffness and, occasionally, a special inner sense of restlessness called akathisia. Effective treatment of such extrapyramidal reactions includes benztropine 1-2 mg up to 4 times daily as needed or diphenhydramine 25 mg 3 times daily.


Class Summary

Used to treat psychoses.

Risperidone (Risperdal)

Binds to dopamine D2 receptor with 20 times lower affinity than for 5-HT2 receptor. Improves negative symptoms of psychoses and reduces incidence of extrapyramidal adverse effects.

Olanzapine (Zyprexa)

May inhibit serotonin, muscarinic and dopamine effects.

Pimozide (Orap)

Antipsychotic of the diphenylbutylpiperidine class. Used to treat delusions of parasitosis and Tourette disorder.



Further Outpatient Care

After medication has cleared the delusions of parasitosis, the agent should be continued for several months and then discontinued. Often, patients come to think that the medication has killed the bugs, and many (but not all) have a remission of their delusions.


If delusions of parasitosis are not treated, scarring can result. The patient's entire life and family may be disrupted by their distress and attempts at treatment.

Therapy for delusions of parasitosis can cause adverse effects. Pimozide can result in tardive dyskinesia and akathisia. Extrapyramidal reactions have been reported to occur in approximately 10-15% of patients taking pimozide. Pimozide can have cardiotoxic effects at high doses. It may cause ECG changes such as prolongation of the QT interval, T-wave changes, and the appearance of U waves.

Lim et al[54] noted an incidence of camphor-related, self-inflicted keratoconjunctivitis secondary to delusions of parasitosis.


Many patients with delusions of parasitosis refuse treatment and are lost to follow-up. For those patients who can be convinced to undertake treatment, the prognosis for a remission of the delusions is good.

Patient Education

Patients must be reassured that they are not alone and that the physician will listen to them and sincerely desires to help them to get better. While one should not say anything to confirm the delusion, it is usually not helpful to forcefully confront patients with delusions of parasitosis.

Statements such as the following might be helpful: "I know you feel strongly that there are parasites here, and I'm sure that you itch severely, but I cannot prove that parasites are or have been the cause of your problem."

For patient education resources, see the Mental Health and Behavior Center.