Clinical Dermatology

Fingernails and toenails can, in a way, be viewed as arising from a “follicle” analogous to that of the hair follicle . The orientation of this “follicle,” of course, lies parallel rather than vertical to the surface of the skin.The nail matrix from which the nail plate grows lies deep to the posterior nail fold. The nail plate, which is made of hard keratin quite similar to that of the hair shaft, grows outward from the matrix. During this outward growth it rests on and is supported by the nail bed. Epidermal cells from the nail bed contribute only a very thin layer of cells to the ventral surface of the nail plate as it grows outward. Keratin produced from the epidermal cells of the overlying posterior nail fold attaches to the dorsal surface of the nail plate to form the cuticle. Damage to the cuticle such as. occurs with “hangnail” formation or overly vigorous manicuring breaks the seal between the cuticle and the nail plate. This creates a blind pocket under the nail fold and allows for the development of paronychial infection.

The lunula of the nail is the crescent-shaped area of whiteness found at the proximal end of the nail plate. It represents the underlying nail matrix as it extends distally from under the posterior nail fold. The lunula is always visible on thumbnails and is usually present on the fingernails.

The opaque, white color of the free distal tip of the nail is due to light refraction from the ventral surface of the free nail plate. The nail plate grows at a rate of about 0.1 mm/ day.

Damage done to the nail matrix will not become visible for several weeks until the damaged nail emerges from underneath the nail fold. The damaged portion then takes an additional several months to traverse the length of the nail bed. Total replacement of a damaged fingernail requires 3 to 4 months of growth, whereas total replacement of a damaged toenail requires 6 to 9 months of growth. A certain amount of ridging and splitting of the nail plate is partly due to aging and partly due to excess dryness of the nails. Some improvement in nail appearance and texture can be obtained with the regular use of a lubricant such as Lac-Hydrin cream.

This entry was posted on Tuesday, August 21st, 2007 at 7:39 am and is filed under Human Anatomy and Physiology. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.