Why are nails black?

Nail black line, the most common reason is nail mother mole, nail mother pigment increased in the body, more common in melanocyte activity enhancement, melanocyte benign, malignant hyperplasia, systemic diseases, or endocrine deficiency caused by nail black line. When nail black line appears widened, and color, shape and other irregularities, should be alert to the occurrence of malignant lesions, timely go to the hospital for examination.