A black line on the thumbnail is considered to be trauma, onychomatous mole, gray nail, etc.
1. Trauma: when the nail area suffers a violent impact, the capillaries underneath the nail will rupture and bleed, and the blood cannot be absorbed in time, so it is manifested as a black line.
2. Mole of nail: Mole of nail belongs to one kind of nevus, the main manifestation is the appearance of black line on the top of the nail, the cause of which is not yet clear, it is caused by the abnormal proliferation of melanocytes in the nail matrix, and the mole of nail has a certain cancerous chance, so it should be paid attention to, and it is recommended to consult the doctor actively and receive treatment.
3. Gray nail: gray nail is a nail lesion caused by dermatophytes invading the nail plate and nail bed, most of them are directly infected by tinea pedis, and the more common causative agent is Trichophyton rubrum, Trichophyton mustelii, Candida, etc., which will damage the nail plate and nail bed, and the nails will be turbid, thickening, separating, and discoloring.
There is a black line on the thumbnail, it is recommended to go to the hospital for consultation and symptomatic treatment for the cause of the disease.