Why, Do You Know, Why Reasons

Do you know the 'why' reasons, or, do the 'whys' often bother you for scientific explanations? For instance, you do know that stars twinkle, but do you know the reasons why, and how? Or, do you know the 'why' reasons behind falling in love? Or, do you know the reasons why dogs bury bones? Probably many of you don’t! Why Corner – the 'why' blog, answers these 'whys' for basic knowledge, with real reasons for the 'why' facts. So, just know them all here if you have the 'why' urge, that is!

Mar 10, 2008

Do you know why it does not pain cutting our nails?

Prof. Know Why answers:

In medical dictionary, nail is defined as “the horny epidermal derivative covering the dorsal aspect of the terminal phalanx of each finger and toe”. Well, in common man’s language, by fingernails and toenails, we understand hard scaley transparent structures that grow at the tip of our fingers and toes. Nails are part of our body. But the amazing thing is that it does not hurt when we cut them short, although it does not happen with other body parts (except hair).

A nail consists of:

  • Eponychium or cuticle - the fold of skin at the proximal end of the nail.
  • Paronychium - the fold of skin on the sides of the nail.
  • Hyponychium - the attachment between the skin of the finger or toe and the distal end of the nail.
  • Nail plate - the hard and translucent portion composed of keratin.
  • Nail bed - the adherent connective tissue that underlies the nail.
  • Lunula - the crescent shaped whitish area of the nail bed.
  • Nail fold - a fold of hard skin overlapping the base and sides of a fingernail or toenail.

But, why it does not pain, cutting our nails? In common usage the word nail usually refers to the nail plate only. Nails are made of a tough protein called keratin and are produced from living skin cells in the fingers and toes. But they do not have nerve endings and pain receptors like the rest of our body. So the pain sensation does not reach our brain and we do not feel pain when they are cut.

But we do feel pain when a nail is plucked, because there are sensory nerves underlying the nail bed and pressure on it is transmitted to these nerves, which results in the sensation of pain. So as long as a nail is attached to the nail bed, harming or cutting it, creates pain. Actually it is the nail bed that causes the pain and not the nail. Thus, when we cut the tip of a nail, where it is detached from the nail bed, we are not hurt.

Usually, nails grow at an average rate of 0.03 centimeters a day (3 cm every 100 days). Fingernails require 3 to 6 months to re-grow completely. Toenails require 12 to 18 months. Precise growth rate of an individual is dependent on age, season, exercise level, and hereditary factors.

And, contrary to popular belief, nails do not continue to grow after death. Actually, the skin shrinks - giving the illusion that the nails grow.

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