What’s the weirdest psychiatric condition you’ve ever heard of? Odds are, this one is infinitely stranger. Delusional Infestation (DI) is a condition in which a person falsely believes that their skin is infested with parasites, insects, bacteria, fungi, or other harmful items (Campbell et al. 2019). They often experience symptoms such as itchy or tingling sensations, or even feel something crawling on or under their skin, which further convinces them that the infestation is real. They may bring “specimens” of the parasites to show their doctors and remain unconvinced when told that the specimens are harmless objects or that medical tests have found nothing physically wrong with their skin.
The condition is also known as Delusional Parasitosis (DP), given that many people who have the condition attribute it to parasites. However, the terminology is changing in response to the fact that a wide variety of both living organisms and inanimate objects are blamed for symptoms (Bewley 2010).
Once it has been established that the person is not actually infested, they may be diagnosed with Delusional Infestation if:
- They have had the delusion for at least a month
- Aside from the delusion, their lives are mostly unimpaired
- Any mood episodes (mania or depression) that have occurred are brief compared to the duration of the delusion
- Their symptoms are not better explained by another physical or mental illness, including schizophrenia, or by substance use* (Campbell et al. 2019)
*If the case is primary DI; more on this in the next section
Causes
The cause of Delusional Infestation depends on the type of DI. Cases where DI is the only condition present are called primary DI. However, a person may also experience DI as a symptom of a different illness or due to the effects of certain drugs. In these situations, they are diagnosed with secondary DI because it is not the primary condition (Wikipedia Contributors 2019).
The cause of primary DI is currently unknown, though it may have something to do with the neurotransmitter dopamine. The presence of unusually high amounts of dopamine in certain brain regions can create formication, the skin-crawling sensation experienced by many people with DI, and faulty dopamine activity has also been implicated in other psychotic disorders like schizophrenia. However, research on this topic is still developing, making it impossible to draw conclusions at this time (Wikipedia Contributors 2019).
Secondary DI has quite a few potential causes. A vast range of physical medical conditions, from AIDS and hepatitis to traumatic brain injury and vitamin B12 deficiency, may cause delusions or crawling sensations (Reich et al. 2019, Wikipedia Contributors 2019). Consuming certain drugs, both legal and illegal, can also create similar effects. The side effects of some prescription drugs include DI, along with alcohol, cocaine, amphetamines, and cannabis (Campbell et al. 2019, Reich et al. 2019). Finally, other, more common mental conditions such as schizophrenia and depression may have symptoms that include DI.
Treatment
Thankfully, we know far more about treating DI than we do about its causes. Symptoms often respond well to antipsychotic medications, and in the case of secondary DI, they may vanish entirely when the person receives treatment for their primary condition (Campbell et al. 2019).
Unfortunately, treatment of Delusional Infestation is often difficult, as by definition, people with DI believe that they have a physical illness, not a mental one. DI cases most often begin in the offices of dermatologists, parasitologists, and entomologists instead of psychiatrists. Upon being shown evidence that their condition is not physical (such as negative test results or proof that a specimen is ordinary detritus), a person may simply leave and go to a different doctor in an attempt to get the diagnosis they want. Recent discussions of DI among researchers and health care professionals have emphasized the importance of collaboration between a person’s doctors and maintaining a positive relationship with patients (Reich et al. 2019, Campbell et al. 2019). These measures can persuade some people with DI to agree to psychiatric treatment, but others may refuse to accept it no matter what.
Potential Harms
Many friends, relatives, and doctors who have seen the effects of Delusional Infestation become frustrated by their inability to persuade the affected person of the reality of their illness. At the same time, it is important to encourage DI patients to accept treatment, as the condition is not harmless. The most obvious problem caused by DI is the stress and mental suffering caused by the symptoms themselves – no one enjoys feeling like they have bugs inside their body! People with DI sometimes scratch or pick at their skin, potentially causing more issues. The symptoms and delusions may also cause problems at work and in social relationships. In rare cases, people with DI may harm themselves, other people, or pets in the course of attempts to get rid of the “infestation” (Shelomi 2026).
A further danger exists in the form of people and organizations who, despite the seriousness of this condition, take advantage of vulnerable people with DI in order to gain money from them. There are multiple pseudoscientific diagnoses promoted in low-quality research and on the Internet that emphasize DI symptoms but cruelly encourage the delusion that the condition has a physical cause. Scary-sounding terms like “Morgellons Disease” and “Neurocutaneous Syndrome” are marketed to the public in order to promote the services of a sketchy doctor or sell a miracle cure (Shelomi 2026). Belief in these false diseases can prevent a person from getting real treatment or unnecessarily prolong their suffering by prompting them to chase after false cures for lengthy periods of time when they could have received help right away.
Overall, Delusional Infestation is an interesting condition that exposes a number of phenomena related to the current state of science and medicine in our society. The need for more effective communication regarding rare conditions, the importance of trust between patients and doctors, and the prevalence of scammers that prey on vulnerable demographics are all important issues that deserve greater examination. DI demonstrates a complicated and strange relationship between our brains and bodies and exposes gaps in our knowledge of medicine and psychiatry. Hopefully in the future, it will get the attention it deserves in the form of more research into its causes and more effective treatments for those who suffer from its symptoms.
Sources:
Bewley, A.P., et al. “Delusional Parasitosis: Time to Call It Delusional Infestation.” British Journal of Dermatology, vol. 163, no. 1, 22 Feb. 2010, pp. 1–2, https://doi.org/10.1111/j.1365-2133.2010.09841.x
Campbell, Elliott H., et al. “Diagnosis and Management of Delusional Parasitosis.” Journal of the American Academy of Dermatology, vol. 80, no. 5, May 2019, pp. 1428–1434, www.sciencedirect.com/science/article/pii/S0190962218330548, https://doi.org/10.1016/j.jaad.2018.12.012
Reich, Adam, et al. “Delusions of Parasitosis: An Update.” Dermatology and Therapy, vol. 9, no. 4, 13 Sept. 2019, pp. 631–638, www.ncbi.nlm.nih.gov/pmc/articles/PMC6828902/, https://doi.org/10.1007/s13555-019-00324-3
Shelomi, Matan. “Delusion or Dentistry: The Pseudoscientific Diagnosis of Neurocutaneous Syndrome | Skeptical Inquirer.” Skepticalinquirer.org, 4 Mar. 2026, skepticalinquirer.org/exclusive/delusion-or-dentistry-the-pseudoscientific-diagnosis-of-neurocutaneous-syndrome/
Wikipedia Contributors. “Delusional Parasitosis.” Wikipedia, Wikimedia Foundation, 16 July 2019, en.wikipedia.org/wiki/Delusional_parasitosis
