The challenge with most COVID-19 related rashes is that it is difficult to discern whether the cause is coronavirus or some other cause.
Many COVID related rashes are likely in what we call the exanthem category. Viral exanthems can be relatively non-specific rashes that start during or even a couple of weeks after exposure and can last 1 to 4 weeks. Biopsies may show non specific changes making it difficult to suggest COVID versus another viral trigger. The challenge in this window of time is that many times the COVID PCR test is negative as these patients may no longer be contagious and their serum antibodies may not be positive yet. In these cases we often are left to assume COVID based on an exposure or timing based on clinical history.
There are some rashes that have been linked to COVID that seem to be more related to vascular phenomenon such as increased risk for clotting. These rashes take on more of a purpuric or bruise-like quality. These may be the underlying trigger for what has been referred to as "COVID toes".
We do have a lot to learn and study with regards to the specific rashes and specific biopsy and blood work findings associated with COVID. The reality is that many patients with these rashes did not present to their dermatologists or make the connection that their skin changed could be COVID related until media reports brought them to patients' attention. For example, we saw relatively few "COVID toes in March of 2020 although we should have likely seen more given the high number of COVID cases. In April 2020, we saw several patients come in with what was likely COVID related skin changes once the media appropriately helped build awareness.