Five skin conditions associated with coronavirus have been identified by dermatologists, according to a new study.

Research was carried out on 375 patients in Spain, in an effort to build a picture of how the disease might manifest in skin symptoms.

Through the Spanish Academy of Dermatology, all the country's dermatologists were asked to help identify patients who had an unexplained skin "eruption" in the last fortnight and who had suspected or confirmed Covid-19.

They were given a questionnaire, and photos were taken of skin conditions to detect patterns of the virus's potential effect on the skin.

But authors of the study, published in the British Journal of Dermatology, warned that in some cases it was hard to tell if skin conditions were directly caused by coronavirus or if they indicated complications.

They also urged the public not to try to self-diagnose Covid-19 based on skin symptoms, because rashes and lesions are common and hard to differentiate without medical expertise.

Chilblain-like symptoms

According to the study, 19% of cases involved chilblain-like symptoms, described as "acral areas of erythema-edema with some vesicles or pustules".

It said these lesions affect the hands and feet and may resemble the small, itchy swellings of chilblains.

They were described as small red or purple spots caused by bleeding under the skin and usually asymmetrical in appearance.

The study said they were associated with younger patients, lasted for an average of 12.7 days, appeared later in the course of Covid-19 and were associated with less severe cases of the disease.

Vesicular eruptions

Described as outbreaks of small blisters, commonly itchy, that appeared on the trunk of the body, dermatologists identified "vesicular eruptions" in 9% of cases.

It said they may be filled with blood, could become larger or more spread out and could potentially affect people's limbs.

Associated with middle-aged patients, they lasted on average 10.4 days, appeared more commonly before other symptoms and were linked with intermediate severity of the disease.

Wheals

Identified in 19% of cases, "urticarial lesions" consist of pink or white raised areas of skin and resemble a nettle rash.

Commonly known as wheals, these are usually itchy and can be spread across the body, including in a few cases on the palms of hands. They were found to last an average of 6.8 days,

Other maculopapules

"Other maculopapules" were identified in 47% of cases and described as small, flat and raised red bumps. They were distributed round hair follicles in some cases and had varying degrees of scaling.

The study said the appearance was similar to pityriasis rosea, a common skin condition.

It said blood spots under the skin might also be present, either as spots or dots or on larger areas. These conditions lasted 8.6 days on average.

They usually appeared at the same time as other coronavirus symptoms, were associated with more severe cases, and itching was very common.

Researchers stressed that maculopapules and urticarial lesions are common and can have many causes, meaning they may not be a helpful aide for diagnosing Covid-19.

Livedo or necrosis

Identified by dermatologists in 6% of cases, livedo or necrosis occurs where circulation in the blood vessels of the skin is impaired, causing it to take on a blotchy red or blue appearance with a net-like pattern.

Necrosis describes the premature death of skin tissue.

Patients showed different degrees of lesions pointing to "occlusive vascular disease", where a narrowing or blocking of arteries occurs, limiting blood flow to certain areas of the body.

The study added that these conditions were associated with older patients with severe cases of Covid-19, although manifestations of the disease in this group varied.

Livedoid and necrotic lesions are relatively rare but the authors said it was difficult to know if they were directly caused by coronavirus, or simply indicated complications.

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