Editing Wrinkle (section)

===Water-immersion wrinkling===<!-- This section is linked from [[Water aging]] -->
[[File:Wrinkly fingers.jpg|thumb|left|A wrinkled finger after a warm bath]]
The wrinkles that occur in skin over prolonged exposure to water are sometimes referred to as ''pruney fingers'' or water aging. This is a temporary [[skin condition]] where the skin on the palms of the hand or feet becomes wrinkly. This wrinkling response may have imparted an evolutionary benefit by providing improved traction in wet conditions,<ref>{{cite journal | doi= 10.1159/000328223 | title= Are Wet-Induced Wrinkled Fingers Primate Rain Treads? |author1=Mark Changizi |author2=Romann Weber |author3=Ritesh Kotecha |author4=Joseph Palazzo | journal= Brain, Behavior and Evolution |  year= 2011 | pmid= 21701145 | volume=77 | issue=4 | pages=286–90| doi-access=free }}</ref> and a better grasp of wet objects.<ref>{{cite journal|last=Kareklas|first=Kyriacos|author2=Nettle, Daniel |author3=Smulders, Tom V |title=Water-induced finger wrinkles improve handling of wet objects|journal=Biol. Lett.|date=January 9, 2013|volume=9|issue=2|doi=10.1098/rsbl.2012.0999|page=20120999|pmid=23302867|pmc=3639753}}</ref> These results were called into question by a 2014 study that failed to reproduce any improvement of handling wet objects with wrinkled fingertips.<ref name=Haseleu>{{cite journal|doi=10.1371/journal.pone.0084949|title=Water-Induced Finger Wrinkles Do Not Affect Touch Acuity or Dexterity in Handling Wet Objects|year=2014|editor1-last=Goldreich|editor1-first=Daniel|last1=Haseleu|first1=Julia|last2=Omerbašić|first2=Damir|last3=Frenzel|first3=Henning|last4=Gross|first4=Manfred|last5=Lewin|first5=Gary R.|journal=PLOS ONE|volume=9|issue=1|pages=e84949|pmid=24416318|pmc=3885627|bibcode=2014PLoSO...984949H|doi-access=free}}</ref> However, a 2020 study of gripping efficiency found that wrinkles decreased the force required to grip wet objects by 20%, supporting the traction hypothesis.<ref name=Davis>{{cite bioRxiv |last1=Davis |first1=N.|date=8 November 2020 |title=Water-immersion finger-wrinkling improves grip efficiency in handling wet objects |biorxiv=10.1101/2020.11.07.372631}}</ref>

Prior to a 1935 study, the common explanation was based on water absorption in the [[keratin]]-laden [[epithelial]] skin when immersed in water,<ref>{{cite web|url=http://www.abc.net.au/science/k2/homework/s95618.htm |title=Dr Karl's Homework – Skin Wrinkles in Water (26/1/2000) |publisher=Abc.net.au |date=2000-01-26 |access-date=2019-04-30}}</ref> causing the skin to expand and resulting in a larger surface area, forcing it to wrinkle. Usually the tips of the fingers and toes are the first to wrinkle because of a thicker layer of keratin and an absence of hairs which secrete the protective oil called [[sebum]].

[[File:Adult sole showing water immersion wrinkling.JPG|thumb|upright|Adult sole showing water immersion wrinkling]]

In the 1935 study, however, Lewis and Pickering were studying patients with [[:wikt:palsy|palsy]] of the [[median nerve]] when they discovered that skin wrinkling did not occur in the areas of the patients' skin normally innervated by the damaged nerve.  This suggested that the nervous system plays an essential role in wrinkling, so the phenomenon could not be entirely explained simply by water absorption. Recent research shows that wrinkling is related to [[vasoconstriction]].<ref>{{cite journal | doi= 10.1002/mus.10323 | title= Water-immersion wrinkeling is due to vasoconstriction|author1=Einar P.V. Wilder-Smith |author2=Adeline Chow | journal=Muscle & Nerve| year=2003| pages=307–311| volume=27| issue=3| pmid=12635117| s2cid= 45193684| doi-access=free}}</ref><ref>{{cite journal | doi=10.1007/s10286-004-0172-4 | author=Einar P. V. Wilder-Smith| title=Water immersion wrinkling| journal=Clinical Autonomic Research| year=2004| pages=125–131| volume=14| issue=2 | pmid=15095056| s2cid=44938772}}</ref> Water probably initiates the wrinkling process by altering the balance of [[electrolytes]] in the skin as it diffuses into the hands and soles via their many sweat ducts. This could alter the stability of the membranes of the many neurons that synapse on the many blood vessels underneath skin, causing them to fire more rapidly.  Increased neuronal firing causes blood vessels to constrict, decreasing the amount of fluid underneath the skin.  This decrease in fluid would cause a decrease in tension, causing the skin to become wrinkly.<ref>{{cite book | title= Dermatotoxicology|author= H. Zhai, K.P. Whilem H. L. Maibach| year=2007| pages=280–281| issue=7}}</ref>

This insight resulted in bedside tests for nerve damage and vasoconstriction. Wrinkling is often scored with immersion of the hands for 30 minutes in water or [[EMLA]] cream with measurements steps of 5 minutes, and counting the number of visible wrinkles in time. Not all healthy persons have finger wrinkling after immersion, so it would be safe to say that sympathetic function is preserved if finger wrinkling after immersion in water is observed, but if the
fingers emerge smooth it cannot be assumed that there is a lesion to the autonomic supply or to the peripheral nerves of the hand.<ref>{{Cite journal | title=Finger wrinkling after immersion in water|author1=G Alvarez, J Eurolo |author2=P Canales| journal=British Medical Journal | year=1980| pages=586–587 | doi=10.1136/bmj.281.6240.586-a | volume=281 | issue=6240 | pmid=7427379 | pmc=1713922}}</ref>