A green patch on the nail cover may be caused by external staining, pathogen infection, anemia, trauma and other factors. 1. External staining: nail contact with some green dyes, hair dyes, may lead to green color on the nail. Occupational factors, such as long-term contact with soap and detergent, may lead to changes in nail color, such as nail plate green. 2. Pathogen infection: Nails are infected by bacteria and fungi, such as Pseudomonas aeruginosa infection, which grows and reproduces and produces toxic products, leading to green color of some nail plates. Such as green nail syndrome, usually can occur in patients whose hands have been immersed in water for a long time or combined with onychomycosis. 3. anemia: patients with iron deficiency anemia, the degree of disease varies, some patients may appear green striped texture of the nail, usually accompanied by dry skin, hyperkeratosis and other symptoms. 4. trauma: consider the possibility that the nails have been hit hard, caused by localized bruising, which will appear as greenish green or blackish black, generally do not need special treatment. External staining causes nails to turn green, it is recommended to carry out cleaning, can be removed. Suspected pathogen infection, anemia and other factors, you can go to the hospital dermatology, hematology, clear diagnosis, but also to give the appropriate treatment.