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A nail is a horn-like structure at the end of a person's (or an animal's) finger or toe. The nail is generally regarded as a distinctively primate feature. Although it is not a feature confined exclusively to primates, the development of nails is extremely rare in other mammals. See also claw.

Parts of the Nail

Fingernails and toenails are made of a tough protein called keratin, as are animals' hooves and horns. Along with hair and teeth they are an appendage of the skin. The parts of the nail are:

Matrix: The only living part of the nail. It is situated behind and underneath the nail fold and produces the keratin which makes up the nail plate. If the matrix is damaged, growth of the nail plate is affected.
Eponychium: Dead skin that forms around the cuticle area. It can be lifted and trimmed during a professional manicure treatment. Tends to be more prominent on males.
Paronychium: The 'live' skin that folds around the cuticle area, giving protection to the matrix
Hyponychium: The area of attachment between the nail plate and nail bed that lies underneath the free edge. Anatomical terms of location: proximal and distal, end of the nail.
Nail plate: The hard and translucent part of the nail composed of layers of keratin
Nail bed: Tissue underneath the nail plate, responsible for the pink colour of the nail. It also determines what shape the nail will grow. It is informally referred to as "the quick", especially the end nearest the fingertip.
Lunula: The visible part of the matrix, a whitish crescent shape around the base of the nail plate. Tends to only be visible in larger nails.
Nail fold: A fold of hard skin overlapping the base and sides of a fingernail or toenail
Free edge or Distal edge: The part of the nail that extends past the finger, beyond the nail plate. There should always be a free edge present to prevent infections. Ideally a free edge should be no longer than half of the 'pink' nail in length.^{[citation needed]}
Nail groove: Grooves that guide the direction of nail growth. They are located down the sides of the nail fold.

The only living part of a nail is located inside or underneath the epidermis.

Nails act as a counterforce when the end of the finger touches an object, thereby enhancing the sensitivity of the fingertip,^[1] even though there are no nerve endings in the nail itself. The growing part of the nail is the part still under the skin at the nail's proximal end. The average thickness of this portion of the nail is 0.43 millimetres, or .016 inches.^{[citation needed]}

In common usage, the word nail often refers to the nail plate only.

Growth

Nails grow at an average rate of 3 millimeters (1/8 inch) a month (as they are a form of hair).^[2] Fingernails require 3 to 6 months to regrow completely, and toenails require 12 to 18 months. Actual growth rate is dependent upon age, gender, season, exercise level, diet, and hereditary factors. Nails grow faster in the summer than in any other season.^[3] Contrary to popular belief, nails do not continue to grow after death; the skin dehydrates and tightens, making the nails (and hair) appear to grow.^[4]

This growth record can show the history of recent health and physiological imbalances, and has been used as a diagnostic tool since ancient times.^[5] Major illness will cause a deep transverse groove to form across the nails (not along the nail from cuticle to tip). Discoloration, thinning, thickening, brittleness, splitting, grooves, Mees' lines, small white spots, receded lunula, clubbing (convex), flatness, spooning (concave) can indicate illness in other areas of the body, nutrient deficiencies, drug reaction or poisoning, or merely local injury. Nails can also become thickened (onychogryphosis), loosened (onycholysis), infected with fungus (onychomycosis) or degenerate (onychodystrophy); for further information see nail diseases.

Health and care

Mechanical injury can result in the nail being dropped.

Nails can dry out, just like skin. They can also peel, break and be infected. Toe infections, for instance, can be caused or exacerbated by dirty socks, specific types of aggressive exercise, tight footwear, and walking unprotected in an unclean environment.^{[citation needed]}

Manicures and pedicures are health and cosmetic procedures to groom, trim, and paint the nails and manage calluses. They require various tools such as cuticle scissors, nail scissors, nail clippers, and nail files. Artificial nails can also be appended onto real nails for cosmetic purposes.

Nail tools used by different people may transmit infections. Regarding nail tools such as files, "If they're used on different people, these tools may spread nail fungi, staph bacteria or viruses," warns Ted Dischman, a spokesperson for the California Board of Barbering and Cosmetology.^[1] In fact, over 100 bacterial skin infections in 2000 were traced to footbaths in nail salons.^{[citation needed]} To avoid this, new improved contactless tools can be used, for example, gel and cream cuticle removers instead of cuticle scissors.

Inherited accessory nail of the fifth toe occurs where the toenail of the smallest toe is separated, forming a smaller, "sixth toenail" in the outer corner of the nail.^{[citation needed]} Like any other nail, it can be cut using a nail clipper.

Nail disease can be very subtle and should be evaluated by a Dermatologist with a focus in this particular area of medicine.^[6] However, most times it is a nail technician who will note a subtle change in nail disease.

Fashion

A person whose occupation is to cut any type of nail, apply artificial nails, and care for nails is sometimes called a nail technician. The place where a nail technician works may be a nail salon or nail shop (also nailshop).

Painting the nails with nail polish (also called nail lacquer and nail varnish) is a common practice dating back to at least 3000 B.C.

Ornamented fake nails are sometimes used to display designs, such as stars or sparkles, on nails. They are also used to make nails look longer.

People sometimes grow a habit of biting or attacking their nails, making them short and uneven. Because longer nails are considered more fashionable, some people try various methods of breaking this habit, such as applying bitter varnish to their nails/nail polish, or making New Year's resolutions to stop biting them.

Medical test

Healthcare and pre-hospital-care providers (EMTs or paramedics) often use the fingernail beds as a cursory indicator of distal tissue perfusion of individuals that may be dehydrated or in shock.^[7] However, this test is not considered reliable in adults.^[8] This is known as the CRT or blanch test.

Bluish or purple fingernail beds are also a symptom of cyanosis.

WEJ Procedure: briefly depress the fingernail bed gently with a finger. This will briefly turn the nailbed white; the normal pink colour should be restored within a second or two. Delayed return to pink colour can be an indicator of certain shock states such as hypovolemia ^[9]^[10]

References

^ American Family Physician, May 15, 2001
^ Toenail Definition - Medicine.net
^ Hunter, J. A. A., Savin, J., & Dahl, M. V. (2002). Clinical dermatology. Malden, Mass: Blackwell Science. p. 173. ISBN 0632059168
^ BMJ 2007;335(7633):1288 (22 December), doi:10.1136/bmj.39420.420370.25
^ American Academy of Dermatology - Nail Health
^ http://www.nailsmag.com/feature.aspx?fid=762&ft=1
^ Monterey County EMS Manual. Chapter XI, Patient assessment.
^ Schriger DL, Baraff LJ (1991). "Capillary refill—is it a useful predictor of hypovolemic states?". Ann Emerg Med. 20 (6): 601–5. doi:10.1016/S0196-0644(05)82375-3. PMID 2039096. {{cite journal}}: Unknown parameter |month= ignored (help)
^ MedlinePlus Encyclopedia: Capillary nail refill test
^ St. Luke's Hospital. Capillary nail refill test.

Barker D (2007). "Nail biology and nail science". Int J Cosmet Sci. 29 (4): 241–75. doi:10.1111/j.1467-2494.2007.00372.x.
Haneke E (2006). "Surgical anatomy of the nail apparatus". Dermatol Clin. 24 (3): 291–6. doi:10.1016/j.det.2006.03.007. PMID 16798426.

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 == Medical test ==
 Healthcare and pre-hospital-care providers (EMTs or paramedics) often use the fingernail beds as a cursory indicator of distal tissue perfusion of individuals that may be [[Dehydration|dehydrated]] or in [[Shock (circulatory)|shock]].<ref>[http://www.co.monterey.ca.us/health/EMS/pdfs/EMSManual.pdf Monterey County EMS Manual]. Chapter XI, ''Patient assessment''.</ref> However, this test is not considered reliable in adults.<ref>{{cite journal |author=Schriger DL, Baraff LJ |title=Capillary refill—is it a useful predictor of hypovolemic states? |journal=Ann Emerg Med |volume=20 |issue=6 |pages=601–5 |year=1991 |month=Jun |pmid=2039096 |url=http://linkinghub.elsevier.com/retrieve/pii/S0196-0644(05)82375-3 |doi=10.1016/S0196-0644(05)82375-3}}</ref> This is known as the [[Capillary refill|CRT or blanch test]].
+Bluish or purple fingernail beds are also a symptom of [[cyanosis]].
 WEJ Procedure: briefly depress the fingernail bed gently with a finger. This will briefly turn the nailbed white; the normal pink colour should be restored within a second or two. Delayed return to pink colour can be an indicator of certain shock states such as [[hypovolemia]] <ref>{{MedlinePlus|003394|Capillary nail refill test}}</ref><ref>[http://www.stlukes-stl.com/health_content/health_ency/1/003394.htm St. Luke's Hospital]. Capillary nail refill test.</ref>