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Some of my friends think that e.g. smiling leads to having wrinkles around your mouth, where your skin folds when you smile, but I'd also count if someone works in the sun a lot an thus squints all the time (if the squinting is causal, not the UV).

A Google search of the claim easily turns up some beauty people saying so. A cursory Google scholar search didn't yield much. In German it may have entered language as "Lachfalten" and in English apparently the equivalent is "laugh lines" though I've never read that.

I was skeptical of the claim, mainly because

  1. I imagine properly testing it would be a very big project (i.e. you'd have to have to rule out a lot of alternatives and ideally do it longitudinally with actual behaviour)
  2. I can easily imagine how such an idea would come about, because people who have such laugh lines may appear more friendly (misinterpretation of wrinkles as facial expression) which leads observers to reconstruct that they must have smiled a lot.

As far as I know Botox works by paralysing the facial muscles whose activity causes wrinkles so I think it's somewhat plausible.

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  • Yes, "laugh lines" is an understood idiom in English for wrinkles near the mouth.
    – Oddthinking ♦
    Commented Jun 18, 2012 at 13:17

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There is a study that was published in 2010, in the British Journal of Dermatology.

An 8-year longitudinal study on the progression of expression lines into persistent wrinkles

  • Methods:  Standardized images were captured at baseline and at 8 years of 122 women (ages 10–72 years, skin types I–VI) with and without a smiling expression. The wrinkle pattern with expression at baseline was compared with the pattern without expression at 8 years. Severity of facial wrinkling was quantified using computer-based image analysis. Skin colour, hydration, sebum and pH were measured at baseline. A structured questionnaire captured demographic and lifestyle data at baseline and at 8 years.

  • Results:  Each subject’s unique pattern of persistent facial wrinkling observed without expression at year 8 was predicted by the pattern of lines observed with a smiling expression at baseline. Having a drier, more alkaline stratum corneum, a lighter complexion, being middle-aged (40s) or becoming menopausal were associated with faster persistent wrinkling.

    Wrinkles
    Temporary facial wrinkles visible only with a smiling expression in 1999 were predictive of and progressed into persistent wrinkles visible without expression in 2008.


    Ethnicity
    African Americans showed the least change in both persistent and temporary wrinkling from 1999 to 2008, significantly less than that of Caucasians

[Additional Source]


Conclusions: 

  • Persistent wrinkles evolve from temporary wrinkles.

  • The pattern of expression lines predicts the pattern of future persistent wrinkles.

  • While skin wrinkling progressively increases over one’s lifetime, the most significant period of change was in the 40s.

  • Certain intrinsic and extrinsic factors are not causative, but influence the rate, of facial wrinkling

  • Lighter and/or dryer skin individuals are more prone to skin wrinkling than their darker and more hydrated counterparts.


More:

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  • 1
    Cool! But does it speak to the matter of whether smiling more actually causes more wrinkles? I thought it pretty likely that persistent wrinkles correspond to facial expression (that's why I mentioned the Botox finding). Or did they assess smile frequency somehow and this is one of the intrinsic factors mentioned in the conclusion?
    – Ruben
    Commented Jun 18, 2012 at 22:07
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    @Ruben - I'm guessing with more wrinkles you mean "become wrinkley more quickly" ? Unfortunately I don't have access to the full paper, but I think it's reasonable to assume that it's a contributing factor. The Mayo Clinic link does say so.
    – Oliver_C
    Commented Jun 19, 2012 at 7:02
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    @Oliver_C: I have a copy of the paper in front of me, and this is what it has to say: ... suggesting that those who show more wrinkles with expression at any given age will tend to show more persistent wrinkles at a later age. Later on, they give an example with smiling temporary pattern that eventually evolves into permanent one, and suggest treatment of not only persistent, but temporary wrinkles when making facial expressions, so it looks that it applies to any type of temporary wrinkles. Contact me if you'd like to study the article itself and include more information in your answer.
    – mindcorrosive
    Commented Jun 19, 2012 at 7:53
  • @mindcorrosive Yes, they say so, but they don't have the evidence (behaviour) to back it up. They cite an identical twin case study though where one twin was repeatedly botoxed (doesn't really tell us much about the amount of natural muscle tensing either). All authors works for P&G Beauty & Grooming. This conflict of interest is acknowledged but the BJD is a flagship journal. I'd love to get to the bottom of this and get a quantification of behaviour's supposed effect.
    – Ruben
    Commented Jun 19, 2012 at 17:06

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