There are many reasons for blackening under the nails, to first see if the recent changes in eating habits and living environment, whether working in a more polluted environment, such as coal mines, heavy industrial bases and other poor working environment, sudden entry will have dust and other substances deposited under the nails accumulation is generally heavier, and even cause skin color changes. In addition to the peripheral blood circulation disorders caused by lack of oxygen will also make the nail bed black, recently, such as living in the foot cold environment or the emergence of autoimmune diseases, affecting the peripheral vascular blood circulation, will lead to the peripheral place of the blood supply is insufficient, the heavier can appear under the nails black. Decreased levels of micronutrients are also susceptible to nail lesions, so check to see if your food and nutrition are well balanced, and if necessary, have your micronutrient levels checked in the hospital.