The normal color of human finger (toe) nails is light red and lustrous. If the human physiological function is disturbed, leading to the occurrence of diseases or malnutrition, trauma, infection, poisoning, application of drugs or changes in the environment and life, it can cause changes in finger (toe) nail color. What are the causative factors of finger (toe) nail color change? 1, black nail: nail plate becomes black, can be caused by the nail mother, nail bed melanocytes produce too much melanin. It can be seen in benign pigmented nevus, malignant melanoma, acanthosis nigricans and other diseases at the nail mother or caused by infection of Aspergillus chimaera, ionizing radiation therapy, heavy metal deposition. Black longitudinal stripes on the nail are commonly seen in chronic eczema, perineuritis, radiation dermatitis, Addison’s disease and other diseases. Black-brown color may appear under the nail when it is healing from traumatic bleeding. Long-term exposure to coal tar, oral arsenic agents, and bismorpholine can also cause black nail. Oral chloroquine can cause blue-black pigmentation of the nail bed. Black longitudinal lines in the nail can also be seen in adult healthy people, especially black people. 2, brown nail (brown nail): mostly seen in post-inflammatory hyperpigmentation, acanthosis nigricans, Addison’s disease, taking antimalarial drugs, mercury poisoning and other metal agents caused. Long-term use of bismorpholine, ethylimine, immersion in potassium permanganate solution can also be caused. 3, blue nail: mostly seen in subxiphoid hematoma, black septic dactylitis. Also seen in the taking of adipine, black uric acid disease, hepatomegaly, hemochromatosis. Patients with silver toxicity have dark blue-gray nail halves. Fixed type drug rash caused by phenolphthalein can cause dark blue changes in the nail bed. 4, the opposite half of the nail: the proximal half of the nail is white, and the distal half is red, pink or brown. There is a clear demarcation between the two halves. Mostly seen in patients with renal disease with azotemia. 5, azure nail halves: mostly seen in patients with hepatomegaly. 6, white nail: divided into 4 types, namely, dotted white nail, linear white nail, partial white nail and full white nail. ① dotted white nail: white spots of variable size and number on the nail plate, generally one to several, commonly seen in children aged 8 to 12 years old, also seen in adults, can be caused by trauma, fungal infection, ascariasis, syphilis and systemic diseases, can also appear in healthy people. ②Linear white nail: horizontal white lines or longitudinal white lines appear on the nail plate, one or several, variable in width, mostly caused by genetic factors, arsenic poisoning, trauma or hypoalbuminemia. ③Partial white nail: the nail plate becomes white in part, mostly caused by tuberculosis, liver disease, nephritis, frostbite, trauma, Hodgkin’s disease, metastasis, leprosy. ④All white nail: mostly caused by heredity, also can be complicated by liver cirrhosis, leprosy, typhoid, ulcerative colitis, nail biting, hairy nematode disease and other diseases. 7, yellow nail: Mostly seen in jaundice, nail fungus caused by yellow ringworm. It can also be caused by excessive consumption of carrots, chronic bronchitis often combined with lymphedema, bronchial expansion and other chronic respiratory diseases. Some are caused by heredity. It is occasionally seen with long-term application of tetracyclines, adipine, topical releasing and anthralin preparations. Also seen in cardiomyopathy, diabetes, pericardial effusion, malignant tumors, syphilis, pustular psoriasis, erythrodermic disease, pericarditis and other diseases. 8, green nail: fungal infection is common, also seen in the nail Pseudomonas aeruginosa infection caused. 9, gray finger (toe) nail: nail plate hyperplasia, thickening or atrophy, brittle, separation of the nail plate and nail bed, cloudy color without luster, dirty gray change, mostly seen in nail fungal disease, also seen in baldness, nail dystrophy, lichen planus, follicular keratosis, chronic eczema, psoriasis and other skin diseases.