Anatomy of Nails
Nails are composed of a hard, strong protein called keratin, as well as small amounts of sulfur, calcium, fats, and water. The nail plate (ie, visible part of the nail) protects the sensitive nail bed underneath it. The folds of skin surrounding the nail on three sides are nail folds. Within the nail plate is the cuticle, which is connected to the nail folds and nail plate, and the lunula (ie, whitish, half-moon-shaped area at the base of the nail). Nails grow from the matrix, an area under the cuticle, at a rate averaging one tenth of an inch per month. Healthy nails grow continuously; serious illnesses can leave behind tell-tale signs called growth arrest lines, also known as Beau’s lines.
Some of the most commonly reported nail problems are also among the most bothersome (aesthetically and emotionally), even though many of them are not medically serious. Others, such as yellow nail syndrome, may be caused by a serious underlying disease. Below are some of the more common complaints.
Paronychia. Paronychia infection of the nail folds can be caused by bacteria, fungi, or viruses. This condition can cause pain, redness, and swelling of the nail folds. It may be seen in people who keep their hands in water for extended periods.
Brittle nails. Brittle nails are one of the most common complaints. They are generally characterized by vertical splitting or separation of the nail plate at the end of the nail. This is often a consequence of aging as the flow of moisture and natural oils to the nail bed declines.
Ingrown toenail. Ingrown toenails typically affect the great (“big”) toe and occur when a corner of the nail curves downward into the skin. This condition can be very painful and lead to infection. Ingrown toenails are usually caused by improper nail trimming, poor posture, or tight shoes. Nails should always be cut longer than the tips of the toe to prevent the advancing edge of the nail plate from “digging in” to the soft tissue of the nail folds.
Nail psoriasis. This nail abnormality occurs primarily in people with psoriasis of the skin; it is seen in about 80 percent of people with inflammatory arthritis associated with psoriasis, especially when the arthritis affects the toes and fingers. Characteristics include yellow-red discoloration of the nail, pitting, separation of the nail plate from the nail bed, crumbling or splitting of the nail plate, and subungual hyperkeratosis (Farber 1992).
Onychomycosis. Approximately seven percent of adults in North America contract this fungal infection. Onychomycosis invades the nail plate, causing the nail to separate from the nail plate (onycholysis) and chalky debris to form under the nail plate (Gupta 1997, 2000). More than 90 percent of cases are caused by one of two pathogens: Trichophyton rubrum or Trichophyton mentagrophytes. Factors that have an important effect on the development of onychomycosis include increasing age; genetics; and the presence of diabetes, acquired immunodeficiency syndrome, or peripheral arterial disease (Faergemann 2003). One multicenter study reported that diabetics are nearly three times more likely to develop onychomycosis than non-diabetics; also, up to one-third of diabetics may develop nail fungus (Gupta 1998).
Pitting. The formation of tiny depressions in the nail plate is known as pitting; it can be caused by any localized skin condition that interrupts natural growth of the nail. Pitting occurs in up to 50 percent of people with psoriasis; it is also a common problem in people with connective tissue disorders (eg, Alopecia areata, Incontinentia pigmenti, pemphigus, Reiter’s syndrome, and sarcoidosis).
White nails (Terry’s nails). This nail abnormality is characterized by a white nail bed with a pink band that is 1 to 2 mm wide at the tip. In most cases, all the fingernails are affected, although it can affect a single finger. White nails affects about 80 percent of people with severe liver disease (Fawcett 2004). It is also seen in people with type 2 diabetes, chronic renal failure, or congestive heart failure and is associated with advancing age (Dolan 2004).