If you look at a human fingernail with a low power hand lens, using the surface of the nail for reference and strong low-angled lighting, you will see that these "grooves" are really tiny parallel RIDGES elevated slightly from the nail's surface;
www.madsci.org/posts/archives/may97/862261432.An.r.html
A very good question. I am sorry for the delay in answering the question. The scientific term for what you are describing is ONYCHOSCHIZIA. It is a vvery common problem and occurs in women more than men. The most common cause is repetitive and prolonged wetting and drying of the nails. Trauma to the fingers ... In some cases,
www.madsci.org/posts/archives/aug2000/966052759.Me.r.ht... www.madsci.org/posts/archives/aug2000/966052759.Me.r.html
A friend, who is rather a wizard at health care, sent me pages copied from a book with the following information on fingernail ridges (now I just need to find out who is the author). ... Lengthwise grooves or ridges may indicate a kidney disorder and is associated with aging. An iron deficiency may also cause ridges.
www.normanallan.com/Med/askdr/finger.html
Nail (anatomy) - Wikipedia, the free encyclopedia
A nail is a horn-like structure at the end of a person's (or an animal's) finger or toe. See also claw. Fingernails and toenails are made of a tough protein called keratin, as are animals' hoove...
en.wikipedia.org/wiki/Nail_(anatomy)
My fingernails have the half moons but I do have the raised grooves on my nails and they are definately more pronounced on the thumbs. Sometime ago I asked a doctor about this condition since I thought for sure it was a prelude to death ... Hello, Just wondering if those fingernail grooves run horizontally or vertically?
www.hcvanonymous.com/SMF/index.php?topic=3037.0
Changes in toenails and fingernails may indicate specific types of illnesses. Following are some of the more common nail problems and what they could mean. ... Lengthwise grooves Kidney disorders, iron deficiency; also associated with general aging.
www.whale.to/a/fingernail_diagnostics.html www.whale.to/a/fingernail_diagnostics.html
A change in fingernail color, thinning, thickening, brittleness, splitting, grooves, Mees' lines and nail ridges, 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.
www.disabled-world.com/health/dermatology/nails/
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www.trans4mind.com/healing/question7.html
(Lengthwise grooves or ridges) - may indicate a kidney disorder (kidney failure); associated with ageing; iron deficiency (Anemia). May indicate a tendency to develop arthritis ... Transverse grooves: may indicate the presence of long-standing illness or malnutrition.
www.hpathy.com/papersnew/traub-finger-nails-homeopathy.... www.hpathy.com/papersnew/traub-finger-nails-homeopathy.asp
Health problems rarely occur in isolation or for obvious reason ... ; Instead of guessing at what might be wrong and hoping that a suggestion will work, wouldn't you prefer to know what is really going on inside your body, based on the many signs it is giving? ... ; Grooves across fingernails; Deformed toenails...
www.digitalnaturopath.com/cond/C76257.html