The nail includes the nail plate, the nail bed and the nail perimeter. Toenail abnormalities involve all three of these components. The factors that cause nail lesions are either congenital or acquired. Congenital nail lesions are often combined with other congenital abnormalities. Acquired nail lesions are seen as a result of microbial infections, local factors. Abnormal changes in the nail in response to systemic diseases or certain skin conditions. There may also be primary nail damage of unknown origin. The mechanism of nail damage is generally related to its etiology. Congenital factors that cause nail lesions and congenital nail disease syndrome are often accompanied by other congenital abnormalities. For example, congenital ectodermal dysplasia and congenital keratinization anomalies. Genetic factors may be present in the family history of the disease. The pathogenesis of nail lesions caused by acquired factors varies, such as infectious nail disease due to pathological changes in the nail plate as a result of inflammatory reactions in the nail groove and nail bed. Non-infectious nail disease can be due to local physical or chemical trauma that can directly damage the nail plate or nail bed or cause abnormal changes in the nail plate due to damage to the nail matrix cells. New organisms occurring in the nail wall or under the nail can cause changes in the nail plate, such as sub nail warts, sub nail hemangioblastoma, sub nail exophytic osteoma, pyogenic granuloma, perineal carcinoma, etc., all of which can affect the deformation and destruction of the nail plate. Certain systemic diseases can cause nail lesions due to endocrine factors, ischemia and hypoxia, and peripheral circulation disorders causing nail plate malnutrition. Certain dermatological diseases have nail lesions as part of their clinical manifestations, such as psoriasis, which can cause nail plate thickening, cross standoffs, and thimble-like pits. Abnormal nail changes can also be caused by lesions invading the nail periphery, such as continuous limb dermatitis and hand eczema.