Redness and inflammation in the hands and feet, referred to as COVID toe condition, may be one of the side effects of COVID-19, a new study published in the British Journal of Dermatology has noted.

Scientists studying the skin condition believe it could be the human immune system's response to the virus which causes COVID-19 and usually develops within one to four weeks of being infected. It can result in fingers and toes becoming swollen or changing colour and also causes some chilblain-type lesions.

"The epidemiology and clinical features of chilblain-like lesions have been extensively studied and published, however, little is known about the pathophysiology involved," said Dr Charles Cassius, the senior author of the study published this week. "Our study provides new insights," he said.

Mostly this particular side effect disappears after a few days but in some cases, the condition can last for a few months. Researchers behind the study, based on blood and skin tests, looked at 50 participants with so-called “COVID toes” and 13 with similar chilblain-lesions that arose before the pandemic.

They discovered two parts of the immune system may be responsible for why the symptoms appear as the body fights off the Cooronavirus. One is an antiviral protein, called Type 1 interferon, and the other is an antibody that mistakenly targets and reacts with a person's own cells and tissues, as well as the invading virus.

Cells lining blood vessels that supply the affected area also appear to play a critical role in the development of COVID toes and chilblains.

Dr Veronique Bataille, a consultant dermatologist and spokesperson for the British Skin Foundation, told the BBC that COVID toe was seen very frequently during the early phase of the pandemic.

However, it has been less common in the current Delta variant wave, which might be down to more people being vaccinated or having some protection against COVID from past infections. "Presentations after vaccination are much rarer," she said.