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A wrinkle, also known as a rhytid, is a fold, ridge or crease in an otherwise smooth surface, such as on skin or fabric. Skin wrinkles typically appear as a result of ageing processes such as glycation,^[1] habitual sleeping positions,^[2] loss of body mass, sun damage,^[3] or temporarily, as the result of prolonged immersion in water. Age wrinkling in the skin is promoted by habitual facial expressions, aging, sun damage, smoking, poor hydration, and various other factors.^[4] In humans, it can also be prevented to some degree by avoiding excessive solar exposure and through diet (in particular through consumption of carotenoids, tocopherols and flavonoids, vitamins (A, C, D and E), essential omega-3-fatty acids, certain proteins and lactobacilli).^[5]

Skin

Causes for aging wrinkles

Development of facial wrinkles is a kind of fibrosis of the skin. Misrepair-accumulation aging theory suggests that wrinkles develop from incorrect repairs of injured elastic fibers and collagen fibers.^[6]^[7]^[8] Repeated extensions and compressions of the skin cause repeated injuries of extracellular fibers in derma. During the repairing process, some of the broken elastic fibers and collagen fibers are not regenerated and restored but replaced by altered fibers. When an elastic fiber is broken in an extended state, it may be replaced by a "long" collagen fiber. Accumulation of "long" collagen fibers makes part of the skin looser and stiffer, and as a consequence, a big fold of skin appears. When a "long" collagen is broken in a compressed state, it may be replaced by a "short" collagen fiber. The "shorter" collagen fibers will restrict the extension of "longer" fibers, and make the “long" fibers in a folding state permanently. A small fold, namely a permanent wrinkle, then appears.

Sleep wrinkles

Sleep wrinkles are created and reinforced when the face is compressed against a pillow or bed surface in side or stomach sleeping positions during sleep.^[9] They appear in predictable locations due to the underlying superficial musculoaponeurotic system (SMAS), and are usually distinct from wrinkles of facial expression.^[10] As with wrinkles of facial expression, sleep wrinkles can deepen and become permanent over time, unless the habitual sleeping positions which cause the wrinkles are altered.^[11]

Water-immersion wrinkling

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,^[12] and a better grasp of wet objects.^[13] These results were called into question by a 2014 study that failed to reproduce any improvement of handling wet objects with wrinkled fingertips.^[14] However, a 2020 study of gripping efficiency found that wrinkles decreased the force required to grip wet objects by 20%, supporting the traction hypothesis.^[15]

Prior to a 1935 study, the common explanation was based on water absorption in the keratin-laden epithelial skin when immersed in water,^[16] 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.

In the 1935 study, however, Lewis and Pickering were studying patients with 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.^[17]^[18] 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.^[19]

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.^[20]

Other animals with wrinkles

Examples of wrinkles can be found in various animal species that grow loose, excess skin, particularly when they are young. Several breeds of dog, such as the Pug and the Shar Pei, have been bred to exaggerate this trait. In dogs bred for fighting, this is the result of selection for loose skin, which confers a protective advantage.^[21]

Techniques for reducing the appearance of aging wrinkles

Current evidence suggests that tretinoin decreases cohesiveness of follicular epithelial cells, although the exact mode of action is unknown. Additionally, tretinoin stimulates mitotic activity and increased turnover of follicular epithelial cells.^[22] Tretinoin is better known by the brand name Retin-A.

Topical glycosaminoglycans supplements can help to provide temporary restoration of enzyme balance to slow or prevent matrix breakdown and consequent onset of wrinkle formation. Glycosaminoglycans (GAGs) are produced by the body to maintain structural integrity in tissues and to maintain fluid balance. Hyaluronic acid is a type of GAG that promotes collagen synthesis, repair, and hydration. GAGs serve as a natural moisturizer and lubricant between epidermal cells to inhibit the production of matrix metalloproteinases (MMPs).

Dermal fillers are injectable products frequently used to correct wrinkles, and other depressions in the skin. They are often a kind of soft tissue designed to enable injection into the skin for purposes of improving the appearance. The most common products are based on hyaluronic acid and calcium hydroxylapatite.

Botulinum toxin is a neurotoxin protein produced by the bacterium Clostridium botulinum. Botox is a specific form of botulinum toxin manufactured by Allergan for both therapeutic and cosmetic use. Besides its cosmetic application, Botox is used in the treatment of other conditions including migraine headache and cervical dystonia (spasmodic torticollis) (a neuromuscular disorder involving the head and neck).^[23]

Dysport, manufactured by Ipsen, received FDA approval and is now used to treat cervical dystonia as well as glabellar lines in adults. In 2010, another form of botulinum toxin, one free of complexing proteins, became available to Americans. Xeomin received FDA approval for medical indications in 2010 and cosmetic indications in 2011.

Botulinum toxin treats wrinkles by immobilizing the muscles which cause wrinkles. It is not appropriate for the treatment of all wrinkles; it is indicated for the treatment of glabellar lines (between the eyebrows) in adults. Any other usage is not approved by the FDA and is considered off-label use.

Laser resurfacing is FDA-cleared skin resurfacing procedure in which lasers are used to improve the condition of the skin.^{[citation needed]} Two types of lasers are used to reduce the appearance of fine lines and wrinkles on the face; laser ablation, which removes thin layers of skin, and nonablative lasers that stimulate collagen production. Nonablative lasers are less effective than ablative ones but they are less invasive and recovery time is short. After the procedure people experience temporary redness, itching and swelling.

References

^ Danby, FW (Jul–Aug 2010). "Nutrition and aging skin: sugar and glycation". Clin Dermatol. 4. 28 (4): 409–411. doi:10.1016/j.clindermatol.2010.03.018. PMID 20620757.
^ American Academy of Dermatology. "Causes of Aging". AgingSkinNet. American Academy of Dermatology. Retrieved 5 March 2013.
^ Cosmetic Procedures for Wrinkles
^ Anderson, Laurence. 2006. Looking Good, the Australian guide to skin care, cosmetic medicine and cosmetic surgery. AMPCo. Sydney. ISBN 0-85557-044-X.
^ Schagen, S. K.; Zampeli, V. A.; Makrantonaki, E.; Zouboulis, C. C. (2012). "Discovering the link between nutrition and skin aging". Dermato-Endocrinology. 4 (3): 298–307. doi:10.4161/derm.22876. PMC 3583891. PMID 23467449.
^ Wang, Jicun; Michelitsch, Thomas; Wunderlin, Arne; Mahadeva, Ravi (2009). "Aging as a consequence of Misrepair—a novel theory of aging". arXiv:0904.0575 [q-bio.TO].
^ Wang-Michelitsch, Jicun; Michelitsch, Thomas (2015). "Aging as a process of accumulation of Misrepairs". arXiv:1503.07163 [q-bio.TO].
^ Wang-Michelitsch, Jicun; Michelitsch, Thomas (2015). "Tissue fibrosis: a principal evidence for the central role of Misrepairs in aging". arXiv:1505.01376 [q-bio.TO].
^ Sarifakioglu, Nedim; Terzioglu, A.; Ates, L.; Aslan, G. (2004). "A New Phenomenon: 'Sleep Lines' on the Face". Scan J Plast Reconstr Surg Hand Surg. 38 (4): 244–247. doi:10.1080/02844310410027257. PMID 15370809. S2CID 25307487.
^ Fulton, James E.; Gaminchi, F. (1999). "Sleep Lines". Dermatol Surg. 25 (1): 59–62. doi:10.1046/j.1524-4725.1999.08073.x. PMID 9935097.
^ Sarifakioglu, Nedim; Terzioglu, A.; Ates, L.; Aslan, G. (2004). "A New Phenomenon: 'Sleep Lines' on the Face". Scan J Plast Reconstr Surg Hand Surg. 38 (4): 244–247 [246]. doi:10.1080/02844310410027257. PMID 15370809. S2CID 25307487.
^ Mark Changizi; Romann Weber; Ritesh Kotecha; Joseph Palazzo (2011). "Are Wet-Induced Wrinkled Fingers Primate Rain Treads?". Brain, Behavior and Evolution. 77 (4): 286–90. doi:10.1159/000328223. PMID 21701145.
^ Kareklas, Kyriacos; Nettle, Daniel; Smulders, Tom V (January 9, 2013). "Water-induced finger wrinkles improve handling of wet objects". Biol. Lett. 9 (2): 20120999. doi:10.1098/rsbl.2012.0999. PMC 3639753. PMID 23302867.
^ Haseleu, Julia; Omerbašić, Damir; Frenzel, Henning; Gross, Manfred; Lewin, Gary R. (2014). Goldreich, Daniel (ed.). "Water-Induced Finger Wrinkles Do Not Affect Touch Acuity or Dexterity in Handling Wet Objects". PLOS ONE. 9 (1): e84949. Bibcode:2014PLoSO...984949H. doi:10.1371/journal.pone.0084949. PMC 3885627. PMID 24416318.
^ Davis, N. (8 November 2020). "Water-immersion finger-wrinkling improves grip efficiency in handling wet objects". bioRxiv 10.1101/2020.11.07.372631.
^ "Dr Karl's Homework – Skin Wrinkles in Water (26/1/2000)". Abc.net.au. 2000-01-26. Retrieved 2019-04-30.
^ Einar P.V. Wilder-Smith; Adeline Chow (2003). "Water-immersion wrinkeling is due to vasoconstriction". Muscle & Nerve. 27 (3): 307–311. doi:10.1002/mus.10323. PMID 12635117. S2CID 45193684.
^ Einar P. V. Wilder-Smith (2004). "Water immersion wrinkling". Clinical Autonomic Research. 14 (2): 125–131. doi:10.1007/s10286-004-0172-4. PMID 15095056. S2CID 44938772.
^ H. Zhai, K.P. Whilem H. L. Maibach (2007). Dermatotoxicology. pp. 280–281.
^ G Alvarez, J Eurolo; P Canales (1980). "Finger wrinkling after immersion in water". British Medical Journal. 281 (6240): 586–587. doi:10.1136/bmj.281.6240.586-a. PMC 1713922. PMID 7427379.
^ The Dog Encyclopedia: The Definitive Visual Guide. Penguin. 15 August 2023. p. 84. ISBN 978-0-7440-8513-6.
^ Stefanaki C, Stratigos A, Katsambas A (June 2005). "Topical retinoids in the treatment of photoaging". J Cosmet Dermatol. 4 (2): 130–4. doi:10.1111/j.1473-2165.2005.40215.x. PMID 17166212. S2CID 44702740.
^ Brin MF, Lew MF, Adler CH, Comella CL, Factor SA, Jankovic J, O'Brien C, Murray JJ, Wallace JD, Willmer-Hulme A, Koller M (1999). "Safety and efficacy of NeuroBloc (botulinum toxin type B) in type A-resistant cervical dystonia". Neurology. 53 (7): 1431–8. doi:10.1212/WNL.53.7.1431. PMID 10534247.