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As the title suggests, I've noticed that my fingernail grow much faster than my toenails. For instance, I usually trim my fingernails every two week or so, but for toenails the number would be about 6 to 8 weeks.

A bit of research revealed this wikipedia article:

In mammals, the length and growth rate of nails is related to the length of the terminal phalanges (outermost finger bones). Thus, in humans, the nail of the index finger grows faster than that of the little finger; and fingernails grow up to four times faster than toenails. [12]

In humans, nails grow at an average rate of 3 mm (0.12 in) a month.[13] Fingernails require three to six months to regrow completely, and toenails require 12 to 18 months. Actual growth rate is dependent upon age, sex, season, exercise level, diet, and hereditary factors. Nails grow faster in the summer than in any other season.[14]

But correlation does not imply causation, so why should the growth rate of nails depend on the length of the terminal phalanges? Then why do babies grow nail much faster? I wasn't satisfied by its answer, so I looked a bit more where I found this other article. They had two possible candidates:

  • because hands are physically closer to the heart than are feet, fingers get better blood circulation and consequently better access to oxygen and nutrients.

  • Fingernails experience almost constant trauma through tapping, typing, bumping, and other seemingly insignificant actions. These persistent minor traumas stimulate fingernail growth. Toes, on the other hand, are not exposed to nearly as much trauma as they are usually bundled up safely inside socks and shoes. Similarly, fingernails on a person's right hand grow faster in right-handed people than on their left hand and vice-versa.

However they don't give actual experimental results. So my question is which of the above is the real cause of this difference in the growth rate of nails; or simply why toenails grow much slower than fingernails?

P.S. The season dependence and the lefthand-righthand asymmetry were news to me; it would be really nice if the answer explains them as well.

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    $\begingroup$ Interesting! We could test "These persistent minor traumas stimulate fingernail growth. " by doing a study of people who primarily walk barefoot (beaches, temperate climate, etc). Mark the toenail, measure actual growth (since they will wear faster, being exposed), and compare it. $\endgroup$
    – Adam Davis
    Commented Nov 13, 2014 at 16:04
  • $\begingroup$ One factor that occurs to me but I don't see mentioned in your research, and this is just from my personal experience but it seems to me toenails are significantly thicker than fingernails. I might be mistaken of course. But if that is the case, could this not account for at least some slower growth ? (as in, even if they have equal growth on a mass basis it would translate to faster length growth if the nail is thinner). $\endgroup$
    – Oosaka
    Commented Mar 8, 2017 at 17:26

1 Answer 1

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Going on the abstract of a study by J.P. Pessan, et al., fluoride intake, as well as "the fact that toenails are less prone to environmental contamination," constitutes a lesser need for growth in toenails than that in fingernails. Also, fluorine being a crucial component in maintaining the solidity of bones, the body may redirect more fluorine that is ingested by various means, to the hands than to the feet, due to the arguably more necessary functions of the hands (in that they are used them for agile and precise motions that tend to influence our survival), meaning less growth in toenails as evidenced in the first citation.

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  • $\begingroup$ are toenails are less prone to environmental contamination? $\endgroup$
    – MmmHmm
    Commented Jan 28, 2017 at 9:40
  • $\begingroup$ Well they are kept in shoes most of the time, whereas we stick our hands in everything. $\endgroup$
    – John
    Commented Aug 23, 2018 at 21:18

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