Nails, like hairs, are made from modified skin cells and consist of dense keratin. Growth occurs from the nail root, or matrix, covered by the skin of the fingers. The growing nail is supported by the nail bed, and the edges are covered by skin folds. The lighter area at the base of the nail is the lunule, and a thin layer of skin - the cuticle - projects from the skin up on to the base of the nail: it is thought to be protective.
The average growth rate is about 0.55mm per week; toe nails grow more slowly than finger nails and different finger nails grow at different rates, with the little finger being the slowest and the middle finger the fastest. Growth rates are reduced and may be stopped by generalised ill health or some medicines.
Disorders affecting nails may be specific to the nails themselves or symptomatic of more generalised disease.
This is relatively common - more so in developed countries, and more so in the feet than the hands (because enclosing the feet in footwear produces the hot and humid atmosphere that fungi love to grow in). The medical term for this is Onychomycosis (from onycho meaning nail, and mycosis which denotes a fungal infection). The usual infecting agent is one of a family called Dermatophytes.
More rarely the nail may be affected by yeasts such as Candida. Infection is more likely in a nail which is already damaged. Initially the nail becomes thickened and yellow, with increasing growth under the nail. There may be separation of the nail from the nail bed (onycholysis). Diagnosis involves growing the fungus from the nail clippings, and treatments are available and may need to be continued for many weeks.
Since many of these conditions arise from pre-existing infection of the feet - athlete's foot - prompt treatment of this may prevent spread of infection to the nail.
These can both affect the nail (see skin section also), and cause a similar appearance, with small dents (called pits) in the surface, thickening and whitening and separation of the nail from the nail bed. Treatment involves topical applications but may be unrewarding, as these conditions tend to recur.
This is the name given to nails that have become thin, pale, brittle and spoon-shaped. It is sometimes found in association with iron-deficient anaemia (as, for example, in the Plummer-Vinsen syndrome where there is a partial occlusion of the pharynx by a pharyngeal web, which bleeds and causes the anaemia). Any case of koilonychia merits investigation. It's an occupational hazard of rickshaw pullers, and is common in the big toe nails of babies.
Means the whitening of the nail bed, where the white crescent-shaped lunule extends upwards towards the fingertip. It may be due to underlying liver disease (such as cirrhosis) or anaemia, but the cause is usually unknown, and it may simply be a normal variant. White spots or ridges on nails are usually due to trauma to the cuticle or the nail bed during growth.
This is infection in the nail fold at the edge of the nail. This commonly follows trauma to the nail (by biting or picking). The finger at the side of the nail becomes red, hot and swollen. The infection may need antibiotics or lancing.
Is the thickening and curvature of a nail - most commonly the big toe nail. It is more often seen in the elderly, and may be a result of neglect or poor circulation. The nails are difficult to trim, and may benefit from the attention of a skilled chiropodist.
Means a bruise under the nail following trauma to the nail bed. The nail is black and painful. Relief may be obtained by drilling a hole in the nail and releasing the blood (a process called trephining). It is felt by some that it is wise to cover the procedure with antibiotics to prevent infection. It's better, of course, to try to avoid hitting the nail in the first place!
Develop when the nail grows into (hence in-growing) rather than over the skin of the nail fold at the edge of the nail. They come about because the edge of the nail has been cut too short, and because shoes are too tight, so the sides of the toe (most commonly the big toe) get cramped upward and overlie the nail. They can be excrutiatingly painful and may require antibiotics and surgery - either to create a smaller nail or to remove the nail completely.
To try and avoid them developing you should cut your toenails so that the edges overhang the underlying toe, and wear wide-toed shoes.
This is where there is increased curvature of the nail with loss of the angle between the nail at its margin with the finger. It is associated with a number of disorders:
This is thought to be due to impaired lymphatic drainage. The nails - all of them - take on a yellow hue and there may be impaired growth. There is often accompanying pleural effusions (fluid on the lung) and swelling of the ankles.
Are a series of transverse (across the nail) depressions which represent a period of impaired growth. This may be due to an episode of severe illness (such as used to be seen with measles) or cytotoxic drugs used in the treatment of malignant disease. All nails are affected.
Are small longitudinal streaks - which look like splinters - where there has been bleeding under the nail. These can occur as a result of trauma (so are seen in manual labourers), in association with psoriasis or as a result of endocarditis - infection or inflammation of the lining of the heart or the heart valves.