About 50% of nail deformities are caused by a fungal infection (see Nail Disorders: Onychomycosis). The remainder result from various causes, including trauma, psoriasis, lichen planus, and occasionally cancer. Drugs, infections, and diseases can cause discoloration of the nails (chromonychia). For example, infection with Pseudomonas bacteria can cause a yellow-green discoloration (see Nail Disorders: Green Nail Syndrome).

The doctor can often make a diagnosis by examination. However, to confirm the diagnosis, the doctor may need to take fungal scrapings and perform a culture (the process of growing the organisms in a laboratory). If the nail's appearance does not improve with treatment of the underlying disorder, manicurists may be able to hide deformities with appropriate trimming and polishes.

Birth Deformities: Some babies are born without nails (anonychia). In nail-patella syndrome (see Hereditary Connective Tissue Disorders: Nail-Patella Syndrome), nails are missing or are small with pitting and ridges. Darier's disease causes red and white streaks on the nails and V-shaped notches to form on the tips of the nails.

Deformities Associated With Disease: Sometimes, diseases that involve other organs can cause changes in the nails as well.

• In Plummer-Vinson syndrome (see Esophageal Disorders: Esophageal Webs), many people have concave, spoon-shaped nails (koilonychia).
• People with iron deficiency may also have spoon-shaped nails.
• Kidney failure may cause the bottom half of the nails to turn white and the top half of the nails to turn pink or appear pigmented (half-and-half nails).
• Cirrhosis may cause the nails to turn white, although the very top part of the nails may remain pinker (Terry's nail). Low levels of the blood protein called albumin (which may occur in people with cirrhosis) may cause horizontal white lines to form on the nails.
• Some lung diseases may cause yellow nail syndrome, in which nails become thick, over-curved, and yellow or yellow-green in color.
• Lymphedema, an accumulation of lymphatic fluid in tissues, also can cause yellow nail syndrome.
• People who have human immunodeficiency virus (HIV) infection, hyperthyroidism, or Cushing's syndrome may have melanonychia striata.

Deformities Associated With Skin Diseases: Sometimes, skin diseases also affect the nail unit and may change the appearance of the nails. Some drugs given to treat skin diseases can change the nail plate. For example, retinoids, such as isotretinoinSome Trade Names
ACCUTANE
and etretinate, can cause dryness and brittleness of the nails.

• In psoriasis, nails may have irregular pits (tiny depressions in the surface of the nail), oil spots (yellow-brown spots under the nail), separation of the nail plate from its bed (onycholysis), and thickening and crumbling of the nail plate.
• Lichen planus of the nail bed causes scarring with early nail ridging and splitting, later leading to pterygium formation. Pterygium of the nail is scarring from the base of the nail outward in a V formation, which leads to loss of the nail.
• People with alopecia areata, a disorder in which round, irregular patches of hair are suddenly lost, may have regular nail pits that form a pattern.
• Trachyonychia—rough, opaque nails—may occur with alopecia areata, lichen planus, atopic dermatitis, and psoriasis. Trachyonychia most frequently occurs in children.

Drugs: Different drugs lead to discoloration of the nail, which usually gets better after the drug is stopped and the nail grows out.

• Chemotherapy drugs such as bleomycinSome Trade Names
  BLENOXANE
  may cause a darkening (hyperpigmentation) of the nail plate. Horizontal (transverse) pigmented or white bands may also be seen in people treated with certain chemotherapy drugs.
• ChloroquineSome Trade Names
  ARALEN
  , a drug used in the treatment of parasitic infections and certain types of autoimmune diseases, can cause the nail bed to turn blue-black.
• Silver, which can be absorbed after occupational exposure or through taking dietary supplements containing colloidal silver protein, can cause the nails to turn a dark blue-gray.
• Drugs that contain goldSome Trade Names
  See Auranofin
  , which is sometimes used in the treatment of rheumatoid arthritis, can turn nails light or dark brown.
• MinocyclineSome Trade Names
  MINOCIN
  , an antibiotic, can cause blue discoloration.
• Zidovudine (AZT), a drug used to treat HIV infection, may cause brown-black longitudinal streaks. However, these streaks can also be present in people who have AIDS but are not receiving AZT.
• Severe arsenic poisoning can cause horizontal white lines to form on the nails.

Melanonychia Striata: Melanonychia striata are brown-black lines in the nail plate caused by the brown pigment melanin. The lines extend from the base of the nail to its tip. In dark-skinned people, these lines may be normal and require no treatment. Similar pigment changes can also be caused by moles or skin cancer around or under the nail, so doctors need to evaluate the surrounding skin.

Onychogryphosis: Onychogryphosis is a disorder in which the nail, most often on the big toe, becomes thickened and takes on an extremely curved, hooked appearance (ram's horn nail). The curved hooked nail may injure an adjoining toe and is caused by one side of the nail growing faster than the other. This disorder involves damage to the nail bed, which is most often caused by repetitive injury (such as by ill-fitting shoes), but may also occur in disorders such as psoriasis. Onychogryphosis is common in older people. The nails should be kept trimmed, and injury to nearby toes can be prevented by placing lamb's wool between the toes. Footwear or stockings that gather at the toes should be avoided.

Onycholysis: Onycholysis is separation of the nail plate from the nail bed or complete nail plate loss. It can occur from trauma (as in prolonged hiking or skiing with ill-fitting footgear); from overzealous nail cleaning; with diseases such as psoriasis and thyrotoxicosis; or from exposure to certain chemicals or drugs. Drugs that cause onycholysis include doxorubicinSome Trade Names
DOXIL
, bleomycinSome Trade Names
BLENOXANE
, captoprilSome Trade Names
CAPOTEN
, 5-fluorouricil, and retinoids. Other drugs, including tetracyclines, psoralens, fluoroquinolones, and quinineSome Trade Names
QUALAQUIN
, may cause onycholysis most often when the nails are exposed to sunlight (photo-onycholysis).

People with onycholysis are at risk of infection with yeast and fungus. Keeping the nail dry and applying antifungal preparations to the nail unit can help. Partial onycholysis may occur in people with a fungal infection.

Onychotillomania: People with this disorder pick at and tear their nails. The most common manifestation is the habit-tic deformity, in which the person frequently picks at or rubs the central cuticle with a neighboring finger. This is most often seen on the thumb and leads to a washboard-like appearance in the center of the nail plate. Onychotillomania can also cause bleeding beneath the nails (subungual hemorrhage), infection in the nail unit, and even complete loss of the nail plate.

Last full review/revision August 2007 by Wingfield E. Rehmus, MD, MPH