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What is Delusional Infestation?

April 18, 2026

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

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  Timothy Durham was convicted of rape when a test showed his DNA genotype matched the DNA recovered from the crime scene. Eye witnesses testified that Durham was in a different state at the time of the incident, but he wasn’t exonerated from his 3000 year sentence until follow up DNA analysis showed that the preliminary forensic analysis used in the trial was misinterpreted (Thomas et al.). DNA testing serves an invaluable part in our criminal justice system, but it comes with complications and bias that can lead to wrongful convictions and misinformed juries.  

Background:

Forensic genetics aims to identify the origin of a biological sample. It can be traced back to Karl Landsteiner who discovered human ABO blood groups. With blood groups, suspects could be eliminated based on their blood type. For example, if a suspect had type A blood and there was type B blood left at the scene by the perpetrator, the investigators could rule out the suspect. Unfortunately, the reverse didn’t work. If the suspect and perpetrator both had the same blood type, it can’t be concluded that the suspect was guilty. Blood identifiers evolved into 8 distinct categories which improved the ability to eliminate suspects, but could only conclude that (if the system matched) it might be the perpetrator or this person might be related to the perpetrator (Jobling and Gill). The field evolved in the 1980s with the discovery of Minisatellites, lines of repetitive DNA that don’t encode proteins. Minisatellite patterns in DNA create what we know today as the DNA fingerprint, and it has a much higher accuracy rate than previous methods (Augustyn et al.). Around the same time, a breakthrough for victims of sexual assault was discovered. In the case of assault, bodily fluids of both the victim and the assaulter can get mixed. A process called differential lysis was created which could selectively increase the concentration of sperm in a fluid sample thereby allowing for accurate DNA testing (Jobling and Gill). Forensics evolved to use single-locus probe testing after several years because of its ease of interpretation. It looked at specific minisatellites that had high variability between subjects. This was the first DNA-based method to be used in a criminal investigation. Two murder homicides from several years apart were connected using DNA evidence. The evidence was then used to exonerate an innocent man, and the guilty party was found when he tried to evade mandatory DNA testing for all men in the small town. His guilt was then reinforced when the DNA profiles matched, and he gave a confession (Jobling and Gill). Finding DNA at a crime scene doesn’t guarantee that you’ll find a murderer. There are issues with non-pure samples and limited samples that make DNA work difficult, and accreditation of facilities and new techniques and take time (Jobling and Gill).  

Subjectivity of DNA Interpretation:

In a 2009 publication, the National Academy of Science discusses the possibility for subjective influence in lab based forensics. The interpretation bias happens in complex cases where, for example, there could be a mixture of DNA. A study published in 2011 looked specifically at this issue. A gang rape happened in Georgia, and the mixture in DNA from the case was used to prosecute one suspect after another suspect took a plea bargain to testify against him. With DNA mixtures, there are three possible conclusions: suspect excluded, suspect cannot be excluded, and inconclusive. If the suspect is excluded, it means that there’s little to no possibility that his DNA is part of the sample. If the suspect cannot be excluded, it means that there’s a possibility that his DNA is part of the sample. In the trial, the DNA examiners who knew the context of the case concluded that the suspect being prosecuted could not be excluded. The 2011 study gave the DNA evidence from this case and the DNA profiles of the suspects to 17 forensic examiners. These examiners had no context of the case, and they all worked independently. Of the 17, only 1 came to the same conclusion (suspect cannot be excluded) as the examiners who knew the context of the case. Twelve of the 17 concluded that the suspect who was prosecuted and convicted had no relation to the DNA found in the sample. Not only does this show that subjectivity occurs due to the context of the case, but the 17 examiners came up with different findings based on their past experiences meaning that not all DNA analysis is objective. Some organizations like the Scientific Working Group on DNA Analysis Methods say that quantitative statistical evidence should be presented with every categorical conclusion, but the US doesn’t require this (Dror and Hampikian).

False Positives:

There are two categories that cause wrongful identification in a DNA report: coincidental matches and false positives. Coincidental matches are DNA matches between two unrelated people. The probability of these matches is about 1 to 500,000 for white individuals and about 1 to 350,000 for black individuals. This small probability of coincidental matches makes people feel confident in DNA evidence. False positives, on the other hand, are matches between DNA and test DNA that result from issues in the forensics lab. There have been multiple cases of forensics labs accidentally switching victim and suspected rapist DNA which lead to convictions that were later overturned when the lab realized the error. There are also cases of misreading or misunderstanding a sample. In a case from 1993, a man was convicted of rape because someone interpreted a mixed sample of victim and perpetrator DNA as an individual sample. The conviction was again overturned. To prevent false convictions, retesting DNA is allowed, but it’s not an efficient solution. Many people are pushing for statistical information on the probability of false positives, so that the jurors can make accurate judgements based on DNA evidence (Thomas et al.).  

Conclusion:

DNA analysis is a useful tool for the criminal justice system, but subjectivity can be an issue in forensic testing. To combat wrongful convictions, there are organizations like The Innocence Project who use DNA testing to free the innocent, but reformed forensic testing standards should be put in place to prevent subjectivity and to ensure juries are correctly informed during trials. https://www.innocenceproject.org/    

Citation:

Augustyn , Adam, et al. “DNA Finerprinting.” Encyclopedia Britannica , 26 Apr. 2018, www.britannica.com/science/DNA-fingerprinting#ref153186. Dror, Itiel E., and Greg Hampikian. “Subjectivity and Bias in Forensic DNA Mixture Interpretation.” Science & Justice, vol. 51, no. 4, 2011, pp. 204–208., doi:10.1016/j.scijus.2011.08.004. Jobling, Mark A., and Peter Gill. “Encoded Evidence: DNA in Forensic Analysis.” Nature Reviews: Genetics, vol. 5, no. 10, Oct. 2004, pp. 739–751., doi:10.1038/nrg1455. Thompson, William C, et al. “How the Probability of a False Positive Affects the Value of DNA Evidence.” Journal of Forensic Sciences, vol. 48, no. 1, Jan. 2003, pp. 1–8., doi:10.1520/jfs2001171.