Gastrointestinal and hepatic diseases during the COVID-19 pandemic: Manifestations, mechanism and management

Figure 4 Facial blackness and dull skin after coronavirus disease 2019 recovery. Three possible mechanisms are shown: (1) Iron in the damaged liver drains into blood vessels. Blood with high iron levels can lead to blackening of the face when it supplies the facial skin; (2) Estrogen cannot be metabolized in the damaged liver. Thus, elevated estrogen in the blood enhances the conversion of tyrosine to melanin; and (3) When liver function is impaired, adrenocortical function is hypoactive, and melanocyte-stimulating hormone increases resulting in an elevation in the secretion of melanin. SARS-CoV-2: Severe acute respiratory syndrome coronavirus 2; MSH: Melanocyte-stimulating hormone; COVID-19: Coronavirus disease 2019.