Black flesh underneath the nails may be caused by trauma, purpura, onychomycosis, pigmented nevus and other reasons. 1. trauma: nails are subjected to external force extrusion, smashing, bumping and other traumatic factors, may lead to capillary rupture, causing black flesh under the nails. 2. Purpura: idiopathic thrombocytopenic purpura, anaphylactic purpura can also cause subcutaneous capillary rupture, resulting in skin hemorrhages, ecchymosis and other symptoms, when the bleeding point in the nail is manifested as black flesh under the nail. 3. Pigmented nevus: for example, benign pigmented nevus or malignant melanoma, which can also lead to black flesh under the nails. 4. Ringworm of the nails: Fungal infection caused by ringworm of the nails may cause changes in the color and texture of the nails, which may also lead to black flesh under the nails. There are many other causes of dark nails (e.g. lichen planus, keratosis underneath the nail, etc.), and it is necessary to clarify the causes under the guidance of the clinician and then carry out the corresponding treatment.