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**][1]

> - **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][2]
> <br>*Temporary facial wrinkles
visible only with a smiling expression in 1999 were
predictive of and progressed into persistent wrinkles visible
without expression in 2008.*
<br><br><br>
>  ![Ethnicity][3]
> <br>*African Americans
showed the least change in both persistent and temporary
wrinkling from 1999 to 2008, significantly less than that of
Caucasians*

>[[Additional Source][4]]

<br>

> **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.

<br>**More:**

 - [The anatomy and pathogenesis of wrinkles][5]
 - [Mayo Clinic - Wrinkles: Causes][6]


  [1]: http://onlinelibrary.wiley.com/doi/10.1111/j.1365-2133.2010.09709.x/abstract
  [2]: https://i.sstatic.net/oVRSv.jpg
  [3]: https://i.sstatic.net/EstOG.jpg
  [4]: http://pgbeautyscience.com/assets/files/posters/AAAS09/Hillebrand%20P101%203MB.pdf
  [5]: http://onlinelibrary.wiley.com/doi/10.1111/j.1365-2133.1985.tb02042.x/abstract
  [6]: http://www.mayoclinic.com/health/wrinkles/ds00890/dsection=causes