But now scientists believe that a new side effect could be linked to the virus, called “Covid toes”.
The team states that the condition typically develops within a week to four weeks of being infected and can result in toes becoming swollen or changing colour.
Symptoms are said to be mild in the majority of cases and the feet return to normal within weeks.
However, scientists say that in some cases the inflammation has continued for more than 150 days and that they fear their findings are “just the tip of the iceberg”.
Dr Esther Freeman, principal investigator of the International Covid-19 Dermatology Registry – the collaboration between the two research bodies – said: “It seems there is a certain sub-group of patients that, when they get Covid, they develop inflammation in their toes, which turns them red and swollen, and then they eventually turn purple.
“In most cases, it is self-resolved and it goes away. It is relatively mild. It lasts on average about 15 days. But we have seen patients lasting a month or two months.”
She added: “What is very surprising is when you get beyond that 60-day mark – because it’s not like patients are resolving at day 70.
(Journal of the American Academy of Dermatology PA/WireJournal of the American Academy of Dermatology PA/Wire)
“It’s the fact that some of our patients are at over 150 days now – these are patients with red or purple or swollen toes for many months.”
Around half of the patients in the registry are reported to have Covid toes and about 16 per cent of those had to be hospitalised as a result, the figures suggest.
Dr Freeman said the identification of people with Covid toes symptoms – including some in the UK – helps scientists understand more about coronavirus-related symptoms elsewhere in the body.
“We are starting to see long Covid in other organ systems, this is the first time we are recognising this can happen in the skin as well,” she explained.
(Journal of the American Academy of Dermatology PA/Wire)
“I think it raises a lot of questions about what sort of inflammation is going on – is there inflammation elsewhere in the body? We don’t really know the answer yet.
“The skin can be viewed as a window into the rest of the body because it is inflammation which you can see – and can be indicative of inflammation elsewhere.”
The figures are submitted by doctors treating patients with skin issues in dozens of countries around the world, meaning there are potentially numerous people with Covid toes who have not sought medical help.
Dr Freeman said that what her team is reporting is “probably just the tip of the iceberg”.
“It’s probably happening a lot more than we’re reporting but I think by reporting it more people will recognise it,” she said.
The figures are being presented at the European Academy of Dermatology and Venereology (EADV) Congress in Switzerland this week.
This is not the first time that researchers have highlighted Covid toes as a potential symptom of coronavirus.
On 29 April, researchers from Spain published a study concerning the “cutaneous manifestations of Covid-19 disease”, cutaneous meaning “relating to the skin”.
The scientists came across five different forms of rashes affecting 375 Covid-19 patients.
These included itchy or painful chilblain-like lesions on the hands and feet, including Covid toes; small blisters on the torso; small, flat and raised red bumps; blotchy red or blue-looking skin; and pink or white raised areas of the skin that looked similar to nettle rash.
Dr John Ingram, editor-in-chief of the British Journal of Dermatology, commented at the time that the investigation was “the most definitive piece of research on the skin features associated with Covid-19 to date”.
“There has been speculation for some time that the virus is responsible for a number of skin signs, but until now these had largely been individual or small scale case reports. This study represents a much more systematic and thorough categorisation of the features,” he stated.
In addition to Covid toes, people around the world have reported experiencing various other side effects they believe could be linked to the virus, including delirium, conjunctivitis and diarrhoea.
You can read more about the lesser known symptoms here.