How Do Nails Know How to Grow Back Even

How do fingernails and toenails, after being damaged to an irregular distal periphery, know to cause more growth at their shortened locations than at their less-damaged locations, so that they soon again have roughly a uniform length across their width?


They don’t.

The longer parts of the nail wear down while the short sections don’t. The apparent result is that the short sections grow faster, but this is an illusion.

Sue from El Paso

Experience is what you get when you didn’t get what you wanted.

Observation certainly proves that what you say is untrue. That is generally my main problem with physicians. Normal nails not damaged grow until they are cut/damaged. If this does not occur, the damaged part catches up in length to the undamaged part. State your authority. . .or is this answer of yours based on watching nails grow? Is this another old physicians’ tale / shamans’ legend?

Ray (Ouch! Cut those things!)

NanoByte, not mine. Mine grow as the guy said.

Nails are inert horn. The base doesn’t know what the tip is doing anymore than your scalp knows what your hair tips are doing.

Nano… do you have a link to a medical journal or something that can substantiate your theory?

“Boy, wouldja get a load of the cloaca on that one”? -Cecil Adams, october 8 1999

May I make a suggestion?

Draw a line across the nail with nail polish. Then damage the nail unevenly, by cutting or whatever other method. Note the progress of the line of polish on your nail. Get back to us in a couple of weeks with the result.

Nanobyte: Do you also believe hair grows faster if you shave?

Sue said the faster growth is an illusion. Then nanobyte said “Observation certainly proves that what you say is untrue.” Do you know what illusion means?

Thank you Sue for your answer.

Virtually yours,


Healthy nails of people in most occupations do not “wear” down. They keep getting longer until they break or someone cuts them. If a nail is well-trimmed and a part of it breaks, and you don’t cut any of the nail, both sides will grow outward, but their lengths will differ less as they do. The longer side does not “wear down”. There is normally nothing around to make it wear down. There appears to be some mechanism that creates more growth on the broken side than on the unbroken side. If there is not, then some other explanation is in order, other than saying the longer portion of the nail “wears down”, or the length equalization is an “illusion”. Cut a nail of yours and “observe” your own “illusion”.

Is DrMatrix an MD or a doctor-lover? There seems to be a bunch of the latter here. If something can be categorized within the “medical realm”, we must suspend objective analysis and let MDs do their role-playing thing? Phooey!

The one from the funny farm:

Drawing a line on your nail with nail polish, of course, won’t prove anything. Your nail, in adjusting the relative lengths of the two different-length portions, will certainly distort, in the adjustment process, the line that you draw.

B_Line 12:

Is your idea of reality what’s written in a medical journal? Do you believe things are necessarily written in medical journals because they were consistently objectively observed. Haven’t you ever noticed how many of such writings start out with claims that end up “proven” by the end of the writing, but with only nebulous associations stated in between? Most of those medical journals would take up far less shelf space if they only had cloacae in them.

Ray (If your nails wear down, quit scratching the blackboard. Role-playing is for fiction; reality requires observation of the real world, not linking to a medical journal.)

I should probably take this to the pit, but I won’t. You sir are an idiot. Nails (both finger and toe) grow from the nail bed that is under the cuticle. The amount “pushed out” is pretty much constant across the width of the nail. I have no idea what your problem with MD’s is, but it does grow tiresome quickly. You asked a question, you got a logical, well thought out answer. You attacked the answer because it was from an MD. You stated that your observations were better than hers. Why? One assumes that you would only observe your own nails, while a Doc, no matter what his specialty, would see many nails.
By the way, nails do wear down, even without cutting. As you drag them across your bed spread, the table, your clothes or skin, you cause friction that erodes the nails.

A hat with bells on is not funny, it is the jester underneath.

I think that was the point.

A doctor-lover? Where? Lynch him. As for that doctor…well, Heaven forbid that just because a person spends 4 years of college and 4+ years in medical school learning about the human body and who knows how many years practicing medicine that she should believe that she could know anything at all about fingernails. She’s obviously deluded. I bet she doesn’t even have any fingernails of her own.

Your Official Cat Goddess since 10/20/99.

Semper Ubi Sub Ubi

As I re-read that last post, I noticed that some sarcasm seems to have crept in. I hope no one was inconvenienced, blinded or scarred for life by that little slip.

Trivia: On the old-fashioned sea-going sailing ships a very common injury was to have all your fingernails popped off. You’ve probably seen in movies where the sailors all scramble up into the rigging and line up along a yardarm, standing on ropes, and start to claw up the sail canvas with their hands. If this was during a storm the wind might pop the canvas as they clawed it up and a lot of the sailors, when they descended, would have bloody hands and be missing most, if not all, their finger nails. And you thought you had a tough job.

In the middle of one of his rants <bNanoByte** asks:

I am not an MD. DrMatrix is just my UserName. If I am not mistaken our friend Sue is an MD. So I quess I am one of the doctor-lovers.
Jeez, chill out.

Strange sort of jester:

You list yourself as “Member”. Do you claim you have authority to take a thread to The Pit?

You, of course, decided I was “an idiot” by reading medical journals and linking to Web pages, right? Is that what Straight Dope means?

Of course, I do not quarrel with that at all.

I agree with that only where the distal edge is more or less equidistant, across its span, from the cuticle.

That’s your opinion, but what is the worth of an opinion of a jester throwing out epithets? It’s clear that what she said was nota “logical, well-thought-out” answer. She claimed the unbroken part of a partially broken-off nail “wears off” so sufficiently as to make it “illusive” that the two sides of the nail conform fairly closely, before the long side grows too long, but at such time as the broken side reaches essentially the desired length. That explanation is clearly just cranked out to fill the gap, so to speak, since, if nails simply “wore” off at such rate, people would not always be cutting them.

I attacked the answer because it made no sense, clearly did not result from even from ordinary observation, and was obviously a stereotypical MD response simply parroting a thesis resultant from the basic rote-learned medical memorization of the fact that the nail grows only from its root end; and that, if it be observed that the two sides grow other than in equal amounts, it is just an “illusion”. Yes, everyone other than MDs, and those who shrink from contesting their half-baked answers, run around seeing illusions all the time.

I stated that her answer made no sense, because observation of my nails and of others practices of having to cut off nails at a frequent rate, if they don’t want them too long, constitutes clear evidence that the amount that normal nails “wear off” is insignificant. I certainly don’t deny that they lose a timy, insignificant amount of their length from wear. I also, however, note what it takes to file down a nail – vastly more abrasian with very rough material, than the nail ever meets otherwise. It would seem to me that a site labeled The Straight Dope would support posting that was not just “professional” hiccups without real-world content. The Web elsewhere is a madhouse of MDs and others jabbering various degrees of “health-care” factoids.

Do you really believe MDs “see” more nails than you do? I don’t know how much, or in what area(s), this MD specializes; but, from her answer, I would have to assume that she spends little time actually observing how nails grow. You’d probably be better informed talking to a mani/pedicurist on this subject (which is not really medical), than to an MD not specialized in nail care (and I don’t know of any that specialize beyond dermatology in general).

And you don’t believe it matters whether this happens at the rate of 3 molecules per day or 0.050" per day? Clearly, you do not care about the importance of the rate at which something happens, so long as you can say it happens.

Yes, I’d say the jester underneath, in this case, comes out quite “funny”. Maybe he has bats where he should have bells.


So, how would you describe the difference in the shape/position of such a line, under the two outcomes that are in conflict in this thread?

You express here exactly the sort of disgusting outlook that provides this society with such in- or negatively effective physicians. And this subject isn’t really a medical one. No MD can become any measure of hero in understanding how finger- or toenails grow/adjust. But, more generally, you throw out the absurdity here that MDs are always spouting – that they should get paid according to how many years it took them to get through school – schooling that mostly consists of simple, rote memory, rather than taxing reasoning ability. I’ve observed those people around Stanford and all the games they play. Role-playing and memorizing is not learning how the body actually works while either whole or damaged.

You figure a little sarcasm will “scar somebody for life”? Maybe you ought to figure out what years in school learning to role-play, when collectively pursued by a whole exclusively society-entrenched profession, can do to people.

Al Zheimers:

An interesting note about the sailors’ fingernails, but I hope it wasn’t intended to impact the issues in this thread. (Not many of us scramble up the rigging these days. . .but if we did, and we lost a fingernail or two, we’d probably sue the ship owners out of existence. :wink: )

Ray (Hit the nail on the head; don’t just wear it down.)

Ray, in the experiment proposed by funneefarmer, the line would remain more or less in it’s original form (though pushed out a little from the cuticle) if you are wrong. If you are right, then the portion of the line nearest the damaged part of the nail should deform outward faster than the rest of the line, leaving a pronounced bell-curve sort of shape.

I may be able to bring in a little experimental data here. When I was a young kid (7? 8? around there), something happened that caused me to have a thumb sucking problem while I slept. Anyway, by the time I went to the doctor, the nail was erroded allmost all the way to the cuticle, but it was eroded in a curve, something to do with the angle I stuck it in my mouth at. So I had ample time to observe the nail grow back, as it took at least a month to do. It grew at a fairly constant rate, the part that was more worn down did NOT grow faster to meet the other end.

Also, for a logical argument, assume Nano is right. The nail grows by being pushed out, not by adding to the front. So all one side growing faster would do is cause that side to push out more, making your entire nail curve off. Also, in response to one of his other posts, the destruction of a nail is far more than a few molecules per day. It is actually shaved off at a good clip. The only thing is that it grows fastert than it is shaved, so it doesn’t appear that way.

I’m starting to wonder if the sun really rises… Just how would a nail know to grow faster on one side if the distal edge on that side was shorter than the other edge? Must be some undiscovered property of keratin. Those bullshit medical journals have obviously neglected this important phenomena; there’s nothing worth reading in them anyway.

Well I’m glad someone thought a real life experiment would be a good way to find out the straight dope. It’s a shame that the original poster doesn’t feel the same way.

I nominate this thread for The Straight Dope “Please Set Claw Depth” award.

Let’s try to be civil to one another.

(I’ll perform Ray’s experiment, but you’ll have to wait awhile for the results. I have snail nails).