Finger and toenails grow at an average rate of 3mm a month. Fingernails take 3 to 6 months to regrow completely, while toenails require around 12 to 18 months to grow back fully. Although some people believe that toenails do not grow back, this is not true. Growth rate depends on age, gender, season, exercise level, diet, and hereditary factors.
Fingernails and toenails are made of a tough protein called keratin and include:
- Nail fold - A fold of hard skin overlapping the base and sides of a fingernail or toenail.
- Nail bed - The adherent connective tissue that underlies the nail, often referred to as the "quick."
- Nail plate - The hard and translucent portion, composed of keratin.
- Hyponychium - The attachment between the skin of the finger or toe and the distal end of the nail.
- Lunula - The crescent shaped whitish area of the nail bed (when visible)
- Free edge - The part of the nail that extends past the finger, beyond the nail plate.
- Eponychium or cuticle - The fold of skin at the proximal end of the nail.
- Paronychium - The fold of skin on the sides of the nail.
Both Fingnails and toenails can also become thickened (onychogryposis), loosened (onycholysis), infected with fungus (onychomycosis) or degenerate (onychodystrophy)
- Onychia is an inflammation of the matrix (surrounding tissue) of the nail with formation of pus and shedding of the nail.
- Onychocryptosis, commonly known as "ingrown nails" can affect either the fingers or the toes. In this condition, the nail cuts into one or both sides of the nail bed, resulting in inflammation and possibly infection.
- Onychodystrophy is a deformation of the nails that can result from cancer chemotherapy. It can include discoloration of the nail, or dyschromia.
- Onychogryposis is a thickening and increase in curvature of the nail most commonly seen in the great toe but may be seen in other toes as well as the fingernails. An affected nail has many grooves and ridges, is brownish in color, and grows more quickly on one side than on the other.
- Onycholysis is a loosening of the exposed portion of the nail from the nail bed, it is frequently associated with an internal disorder, trauma, infection, nail fungi, allergy to nail enhancement products, or side effects of drugs.
- Onychoschizia or splitting of the nails is a very common problem often seen by dermatologists. The term onychoschizia includes splitting, soft or thin toenails and fingernails.
- Onychomadesis is the separation and falling off of a nail from the nail bed. Common causes include localised infection, minor injury to the matrix bed, or severe systemic illness.
- Onychomycosis, also known as tinea unguium, is a contagious infection of the nail caused by the same fungal organisms which cause ringworm of the skin.
- Onychoptosis is the periodic shedding of one or more nails, in whole or part. This condition may follow certain diseases such as syphilis, or can result from fever, trauma, systemic upsets or adverse reaction to drugs.
- Paronychia is a bacterial or fungal infection where the nail and skin meet.
- Koilonychia is when the nail curves upwards due to an iron deficiency. The normal process of change is: brittle nails, straight nails, spoon-shaped nails.
- Subungual hematoma occurs when trauma to the nail results in a collection of blood, or hematoma, under the nail. It may result from an acute injury or from repeated minor trauma such as running in undersized shoes.