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COVID can affect the skin in a variety of ways. Some people may experience a widespread maculopapular rash (flat or raised areas of discoloured skin), while others might present with hives (raised areas of itchy skin). Most COVID skin lesions tend to go away after a few days, or in some instances a few weeks, without the need for any specialised treatment.

"COVID nails" encompasses changes such as:

Beau's lines – horizontal indentations that occur at the base of the fingernails or toenails when there's a temporary interruption in nail growth due to a physical stress on the body. Mees' lines – horizontal white lines that appear on the nails, thought to be caused by the abnormal production of proteins in the nail bed. A red half-moon pattern which develops at the base of the fingernails (the mechanism underlying this change is unclear).

Hair loss is perhaps an understated symptom of COVID-19, usually occurring one month or more after the acute infection. In one study of almost 6,000 people who had previously had COVID, hair loss was the most common post-COVID symptom, reported by 48% of participants. It was especially prevalent among people who had severe COVID and white women.

As with other viral infections, such as the flu and measles, COVID has been found to affect the cells in the inner ear, with hearing loss or tinnitus (a constant ringing sensation in the ear) sometimes following infection. In a review study that included 560 participants, hearing loss occurred in 3.1% of patients with COVID, while tinnitus occurred in 4.5%.

We don't understand exactly what causes these symptoms, but we know the most important part is played by a process called inflammation. Inflammation is our body's natural defence mechanism against pathogens; SARS-CoV-2 in this case. It involves the production of "cytokines" – proteins which are important in controlling the activity of immune cells.