The nails that cover the tips of our fingers and toes are made up of a protein called keratin. The nail structure formed by keratin is hard and water-proof, and functions to protect the soft underlying nail bed. Our nails keep growing throughout our life, although the rate of growth decreases as we age. Even though we see the nails as one continuous structure, it is actually made up of several parts. Different fingernail abnormalities may arise from a problem in different parts and not in the fingernail as a whole as it may appear.
Parts of the Fingernail
The parts of a nail can be described as follows:
- Matrix: The matrix is the source of nail growth. The cells from the matrix contribute to the keratinized layers that form the visible nail plate, which covers and protects the nail bed. The nail plate grows distally as new cells from the nail matrix contribute to the proximal end. Diseases, poor blood circulation and inadequate nutrition can all affect nail growth by affecting the cells in the nail matrix.
- Bed: The nail bed lies beneath the nail plate. It is continuous with the skin that surrounds the nail, and has capillaries that give healthy nails its characteristic light pink color. The nail bed also contributes to the keratin of the nail plate, although not to the extent that the nail matrix does.
- Plate: When people talk about the nail, they are generally referring to the visible nail plate on the tips of fingers. The nail plate is made up of layers of keratinized dead cells. In this regard, it is similar to the hair and the outermost layer of the skin.
- Folds: The nail plate is held in place on three sides by the nail folds: one proximal nail fold, and two lateral nail folds. The distal end of the nail plate is the only free end.
- Cuticle: Nail cuticle is a thin and translucent part of the skin that covers the proximal part of the nail plate. Also known as the eponychium, the nail cuticle seals the proximal end of the nail plate and helps in preventing infection of the nail root and the nail matrix.
- Lunula: The lunula lies at the base of the nail plate and is a part of the nail matrix. It is crescent-shaped and whitish in color.
The status of our overall health can be reflected in the condition of our nails to some extent. Healthy nails are light pink in color, with the lanula being a shade or two lighter, or even white in color. The nail plate has a smooth, curved surface, and is also flexible but does not crack easily unless subjected to significant force.
Discoloration of nails and deformities in the nail structure can be indicators of some health problems. However, some features that may look abnormal are not a cause for concern. Some of these normal features that may look out of place are:
- Longitudinal ridges: These ridges lie along the length of the nail plate (from the proximal cuticle to the free distal edge). These longitudinal ridges are a normal feature of the aging process, and should not be mistaken for a sign of any disease.
- Nail beading: The surface of a healthy nail plate is smooth and curved. With age, it may also become rough, and may have a beady appearance. Excessive beading may, however, reflect an underlying medical condition (for example, rheumatoid arthritis).
- White specks and lines: Air spaces within the nail plate may give the appearance of white specks and lines. This should not be taken as a sign of calcium deficiency.
Other abnormalities in the appearance of nails may indeed be indicative of an underlying medical condition.
Paronychia refes to inflammation and swelling of the nail folds. This can occur along any of the three edges where the nail plate is held, and is mainly caused by an infection. The most common infectious agents that cause inflamed or swollen nail folds are bacteria and fungi. Bacterial infections of the nail folds mostly occur after a trauma to this region. The most common reason for the trauma is nail biting, which gives an opportunity for the bacteria in the mouth to enter the nail bed via the injury site.
In fact, paronychia may be a recurrent theme in people who have a habit of biting their nails. Fungal infections are associated with long term use of nail cosmetics such as acrylic nail extensions. Fungal infection of nail folds may also be secondary to infections elsewhere in the body.Other than infection, paronychia can also be caused by factors such as excessive manicuring, chronically wet hands, diabetes and poor peripheral circulation. Inflammation of nail folds may also be a result of connective tissue diseases such as dermatomyositis, systemic lupus erythematosus (SLE), and systemic sclerosis.
Read more on nail fungus.
Ridges and furrows on the nails
A variety of different ridges and furrows can form on the nail plates in various conditions. For example, systemic medical conditions such as septicemia, myocardial infarction, hypotensive shock, hypocalcemia, chemotherapy, and zinc deficiency may cause formation of a transverse groove (technically known as Beau’s line) on the nail plate. Many transverse ridges on the nail plate can be seen in conditions such as psoriasis, eczema, chronic paronychia, and habitual tic-dystrophy. Longitudinal ridges and brittle nails can be seen in conditions such as rheumatoid arthritis, lichen planus, Darier’s disease, and peripheral vascular disease. Iron, protein and folic acid deficiencies may cause a central longitudinal ridge on the nail plate.
Curved and pitting nails
A variety of medical conditions also affect the curvature of the nails. For example, a spoon-shaped depression in the nail plate (technically known as Koilonychia) can appear in conditions like iron-deficiency anemia, SLE, Raynaud’s disease, diabetes mellitus, lichen planus, and protein deficiency. Koilonychia may even be caused by prolonged exposure to certain detergents. Depressions or pits in the nail plate may be seen in alopecia areata, psoriasis, eczema, and lichen planus. These pits may be small or large, with regular or irregular boundaries. Excessively curved nails that resemble the beak of a bird are associated with conditions such as hyperparathyroidism, psoriasis, renal failure, and systemic sclerosis.
Conditions that cause swelling or clubbing of the fingertips also distort the nail shapes. The nails assume an extremely curved shape when the associated digits get swollen. Some conditions that cause digital clubbing are asbestosis, berylliosis, mesothelioma, lung cancer, cystic fibrosis, sarcoidosis, congenital heart disease, infective endocarditis, inflammatory bowel disease, biliary cirrhosis, and hyperthyroidism.