The human nail is a plate of keratin that lies on the tips of the fingers and toes. The main purpose of the nails are to protect the fingers and toes, however, the fingernail also assists with certain physical activities in daily life.
The human nail is constantly growing and being removed by clipping or biting. In childhood, it takes the nail about 3 months to grow out completely while this may take up to 6 months in the elderly.
Like any part or organ of the human body, the condition of the fingernails and toenails are dependent on the general health status. Therefore changes and defects in the nails may be indicative of certain systemic diseases.
While the word ‘nail’ is used to describe the nail bed, the entire human nail involves many other parts, some of which are not visible from the exterior.
Parts of the Nail
The matrix is the source of the cells that become the keratinized layers of the nail plate. It is located deep in the nail sinus. As new cells grow, it pushes out the nail plate replacing it with new keratin at the proximal part of the nail plate that lies adjacent to the matrix.
Poor circulation, inadequate nutrition and localized or systemic diseases can affect the growth of the new cells to make up the nail plate.
The nail bed lies underneath most of the nail plate and is a continuation of the skin around the nail. It contributes to the keratin of the nail plate although it is to a lesser degree than the matrix. Blood in the dermal capillaries of the nail bed give the nail its characteristic light pink color.
This the largest part of the nail and is composed of laminated layers of keratin. It is similar in structure to human hair and skin and is made up of dead cells.
The proximal edge of the nail plate is the nail root which emanates from the nail sinus. It extends across the fingers and toes to protrude from the tip (depending on the length). This free end of the nail is also known as the distal edge, while the sides are known as the lateral edges.
The nail plate is smooth and curved and light pink in color due to underlying dermal capillaries in the nail bed. Changes in the nail color may be linked to various diseases which are discussed under Discolored Nails.
At times, ridges, lines, changes in thickness and discoloration may arise as a result of disease. This is discussed further under Fingernail Ridges.
Non-pathlogical changes of the nail plate, include :
- longitudinal lines or ridges which occurs with age.
- beading, which is the loss of the smooth curved surface of the nail plate, may normally occur with age although severe beading may be indicative of disease.
- white dots, specks or lines on the nail plate (striae leukonychia) is a sign of airspaces within the nail plate and is not related to a calcium deficiency.
- The nail folds surround and supports the nail plate on all 3 sides. It is the junction of the skin and nail plate and may sometimes be slightly darker in color thereby forming a clearly demarcated margin from the surrounding skin.
- The proximal fold lies over the nail root and matrix. The lateral nail folds extend from the proximal folds and runs alongside the nail plate to terminate near the tip of the finger or toe.
- The most distal part of the lateral nail fold is often prone to trauma from mechanical injury, nail biting and ingrown nails as well as bacterial and fungal infections. Inflammation and swelling of the folds is known as paronychia.
- Also known as the eponychium, it is the part of the skin that overlaps onto the proximal part of the nail plate. It provides some, although minor, support for the nail plate but more importantly, the cuticle seals the nail sinus to prevent injury and infection of the nail root or matrix.
- The cuticle is usually thin, translucent and extends a short distance over the lunula or nail bed. It has neat margins. Ragged cuticles or uneven cuticles may be the sign of excessive manicuring, poor nail care with overuse of the hands or it can be a sign of certain connective tissue diseases.
- This is the crescent shaped area at the base of the nail plate and is usually pale white to light pink in color. It is an extension of matrix and if most evident on the thumb. A lunula with a pointy tip is possibly a sign of excessive manicuring.