Blackening of the edges of the toenail cap can be caused by a number of factors, such as bleeding under the nail, staining, and nail fungus.
1. Bleeding under the nail: after the toenail is damaged by external force, there is bruising under the nail, which can also cause the blackening of the nail and its edge, and usually can be absorbed gradually.
2. Toenail cover edge staining: If the shoes and socks are black and decoloration occurs, or the toenail comes into contact with dyes, it may lead to blackening of the edge of the toenail cover, which can disappear after cleaning.
3. Nail fungus disease: the formation of nail fungus disease is mainly caused by fungal infection, which can appear finger (toe) nail discoloration, become cloudy, thickening, brittle and other abnormal changes.
If the edge of the nail cap of the foot becomes black, such as the symptoms persist, or accompanied by nail thickening, brittle and other abnormal manifestations, you should consult a doctor in a timely manner, to clarify the cause of the disease after treatment.