Dr. Amy Paller/Northwestern University via AP
- Lesions on the toes that make them look frostbitten have been reported after COVID-19.
- A study of so-called COVID toe found it could come from the immune system overreacting
- The findings add to a growing body of evidence that suggests COVID-19 caused the lesions.
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A study into the phenomenon called "COVID toe," skin lesions that appear after catching the coronavirus, may have been explained by a new study.
The work, based on cases from Paris, suggests that the problem could be caused by an overly aggressive immune response from the body.
A study, which is contributing to a growing body of evidence supporting that COVID-19 caused the condition, provides a snapshot of the immune reactions in the COVID-19 toes.
Their findings were published in the peer-reviewed British Journal of Dermatology on Tuesday.
Cases of "COVID toe" started appearing at the beginning of the pandemic. They are characterized by feet looking a little like they have been frostbitten: purple hue, swollen toes, and red, itchy plaques on the extremities.
The sores can be extremely painful, causing an itching or burning sensation, The New York Times previously reported.
By April 2020, the American Academy of Dermatology had received about 100 submissions of people seeing these kinds of lesions on their hands and feet, Insider's Yeji Jesse Lee previously reported.
Scientists have debated whether these were just fluke appearances or if these cases were caused by the COVID-19 coronavirus.
In the new study, scientists looked at 50 cases of COVID toe that came to the Saint-Louis Hospital, Paris, France, in the spring of 2020.
Based on blood and skin biopsy tests, the researchers found that the toes were showing abnormal levels of a molecule called interferon 1.
The molecule is life-saving during infections. It acts as a first line of defense by activating the immune system to fight off viruses.
But the molecule might be working too hard. It seems to be recruiting immune cells to the area, the study said, which could cause damage in parts of the body where blood vessels are most narrow, like toes.
The scientists also found that the COVID-19 toes had antibodies that were attacking the body, not just the virus.
The good news is that local or systemic anti-inflammatory treatment could reverse COVID toes, the scientists said in the study.
"COVID toes" were seen most at the start of the pandemic. They have been less common during the Delta wave, Dr. Veronique Bataille, a consultant dermatologist and spokeswoman for the British Skin Foundation, told the BBC.
This could mean that the vaccination or immunity from previous infection is helping present the apparition of COVID-19 toe, per the BBC.
This would make sense, since vaccines effectively reduce the risk of severe disease and death from COVID-19.