"By a man's fingernails...a man's calling is plainly revealed." So says Sir Arthur Conan Doyle in a Study in Scarlet, speaking as the famous detective Sherlock Holmes. Besides occupation, the nails may reveal one's habits, anxiety level, and certain health problems.
Pale Nails
White nails with a rim of darker color at the tip of the nail is called Terry's nail and rarely a sign of a severe liver disease called cirrhosis. Most people with this nail change are otherwise in good health.
White Nails
Although totally white nails present since birth may be an inherited condition with no implications as to general health, if it occurs later in life, it may be a sign of several systemic diseases, including cirrhosis, chronic renal failure, congestive heart failure, diabetes mellitus, chronic hypoalbuminemia, and Hodgkin's lymphoma.
Yellow Nails
The so-called "yellow nail syndrome" occurs in patients with serious pulmonary disease and lymphedema (swelling of the extremities). In these patients, most if not all of the nails are yellowish.
Bluish Nails
In this condition, the nails are really normal in color but the nail bed, the tissue that lies beneath the nail plate, is blue. This is commonly called nail bed cyanosis and is a sign of poorly oxygenated blood or more accurately unoxygenated hemoglobin, the oxygen carrying protein in red blood cells.
Rippled Nails
Nail pitting is a classical sign of psoriasis in the nail. This appears as tiny holes in the nail surface. Rippling of the nail surface is seen in patients with dermatitis of the fingertips. This can be a result of atopic dermatitis, irritant dermatitis, or allergic contact dermatitis.
Split or Cracked Nails
Brittle nails, onychoschizia and onychorrhexis, are often a condition of the elderly.
Puffy Nail Fold
The skin around the edge of the nail can be damaged by many things. It is unusual in that aside from the retina the capillary morphology can be evaluated using magnification. Damaged capillaries caused by certain autoimmune collagen vascular disease can give the skin and cuticle a "moth-eaten" appearance.
Dark Lines Beneath the Nail
There are a number of reasons for the appearance of a linear brown or black streak extending from the cuticle to the tip of the nail. Since it is not possible to visualize the source of the color since it resides in the nail matrix below the nail fold, it is frequently a cause for anxiety in the patients and their doctors. A biopsy may be required in order to be sure it is not a form of skin cancer.
Gnawed Nails
As with any unpleasant habit, the cooperation of the patient is necessary to modify the behavior. It would be unusual that this sort of addiction would signal the appearance of some deep underlying psychopathology.
Nails Are Only Part of the Puzzle
Changes in the nails occasionally may signal a significant systemic disease. Most of the time, nail signs are self-limited and tend to resolve on their own. Patience is a necessity in dealing with nails because their turnover is slow. It may take many months for a damaged nail to replace itself entirely.