The disease usually develops between a week and four weeks after infection and can lead to swelling of the toes or a change in color.
Symptoms would be mild in most cases and the feet will return to normal within a few weeks.
Scientists have also found that about one in six people require hospital treatment, while some of those with symptoms of “long Covid” report cases that last for several months.
Dr Esther Freeman, principal investigator of the International Covid-19 Dermatology Registry, the collaboration between the two research organizations, said: “It appears that there is a certain subset of patients who when they contract Covid , develop inflammation of the toes. , which makes them red and swollen, and then they eventually turn purple.
“In most cases, it resolves spontaneously and goes away. It is relatively light.
“It lasts an average of 15 days. But we’ve seen patients last a month or two. “
She added: “What’s very surprising is when you go over that 60 day mark – because it’s not like patients are resolving on day 70.
“It’s the fact that some of our patients are over 150 days away now – they are patients with red or purple toes or swollen for several months. ”
About half of the patients in the registry are believed to have Covid toes and around 16% of them had to be hospitalized as a result, the figures show.
Dr Freeman said identifying people with symptoms of Covid toes – including some in the UK – helps scientists better understand symptoms related to coronavirus elsewhere in the body.
She said: ‘We are starting to see Covid in other organ systems for a long time, this is the first time that we recognize that it can also occur in the skin.
“I think that raises a lot of questions about what kind of inflammation is going on – is there inflammation elsewhere in the body?
“We don’t really know the answer yet.
“The skin can be thought of as a window to the rest of the body because it’s inflammation that you can see – and that can be a sign of inflammation elsewhere. ”
The figures are submitted by doctors treating patients with skin problems in dozens of countries around the world, meaning that there are potentially many people with Covid toes who have not requested assistance. medical help.
Dr Freeman said: ‘I think what we are reporting is probably just the tip of the iceberg – it is probably happening a lot more than what we are reporting, but I think that by reporting it more people will recognize it. ”
The figures are presented this week at the congress of the European Academy of Dermatology and Venereology (EADV) in Switzerland.