Cells of the nail matrix divide, move outward and cornify to become the nail plate. The nail plate then slides forward over the nail bed. As the end of the plate extends beyond the nail bed it is filed, trimmed or worn away. Fingernails are replaced in about 4-6 months as they grow outward at a rate of about 0.1 mm per day. Toenails grow more slowly and are replaced every 8-12 months.
Growth rates vary with age, season and nutrition.
Local and systemic disease can produce changes in nail growth and appearance. Pitting and ridging of the nail matrix usually result from inflammation of the nail matrix. Changes in the color of the nail bed can result from numerous conditions ranging from local to systemic disorders. Risk factors for the development of nail abnormalities include excessive exposure to water and solvents, trauma to the nails, irritants, drug exposure, infections, dermatologic conditions and underlying disease of the pulmonary, cardiovascular or gastrointestinal systems. Disease of the Nails Paronychia is a bacterial , fungal or viral infection of the tissues around the nail that causes pain, swelling, throbbing and redness.