Arrector pili muscle

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NerveSympathetic postganglionic nerve fibers
Anatomical terms of muscle

The arrector pili muscles, also known as hair erector muscles,[1] are small muscles attached to hair follicles in mammals. Contraction of these muscles causes the hairs to stand on end,[2] known colloquially as goose bumps (piloerection).[3]


Each arrector pili is composed of a bundle of smooth muscle fibres which attach to several follicles (a follicular unit).[4] Each is innervated by the sympathetic division of the autonomic nervous system.[4] The muscle attaches to the follicular stem cell niche in the follicular bulge,[3][4][5] splitting at their deep end to encircle the follicle.[6]


The contraction of the muscle is involuntary. Stresses such as cold, fear etc. may stimulate the sympathetic nervous system, and thus cause muscle contraction.[4]

Thermal insulation[edit]

Contraction of arrector pili muscles have a principal function in the majority of mammals of providing thermal insulation.[4] Air becomes trapped between the erect hairs, helping the animal retain heat.

Self defence[edit]

Erection of the porcupine's long, thick hairs causes the animal to become more intimidating, scaring predators.[citation needed]

Sebum excretion[edit]

Pressure exerted by the muscle may cause sebum to be forced along the hair follicle towards the surface, protecting the hair.[7]

Hair follicle stability[edit]

Arrector pili muscles also stabilise the base of the hair follicle.[5][6]

Clinical significance[edit]

Skin conditions such as leprosy can damage arrector pili muscles, preventing their contraction.[8]


The term "arrector pili" comes from Latin. It translates to "hair erector".[1]

Additional images[edit]


  1. ^ a b "Anatomy of the Skin | SEER Training". Retrieved 2021-01-21.
  2. ^ David H. Cormack (1 June 2001). Essential histology. Lippincott Williams & Wilkins. pp. 1–. ISBN 978-0-7817-1668-0. Retrieved 15 May 2011.
  3. ^ a b Fujiwara, Hironobu; Ferreira, Manuela; Donati, Giacomo; Marciano, Denise K.; Linton, James M.; Sato, Yuya; Hartner, Andrea; Sekiguchi, Kiyotoshi; Reichardt, Louis F.; Watt, Fiona M. (2011-02-18). "The Basement Membrane of Hair Follicle Stem Cells Is a Muscle Cell Niche". Cell. 144 (4): 577–589. doi:10.1016/j.cell.2011.01.014. ISSN 0092-8674. PMC 3056115. PMID 21335239.
  4. ^ a b c d e Pascalau, Raluca; Kuruvilla, Rejji (August 2020). "A Hairy End to a Chilling Event". Cell. 182 (3): 539–541. doi:10.1016/j.cell.2020.07.004. ISSN 0092-8674. PMID 32763185. S2CID 221012408.
  5. ^ a b Torkamani, Niloufar; Rufaut, Nicholas; Jones, Leslie; Sinclair, Rodney (2017-01-01). "The arrector pili muscle, the bridge between the follicular stem cell niche and the interfollicular epidermis". Anatomical Science International. 92 (1): 151–158. doi:10.1007/s12565-016-0359-5. ISSN 1447-073X. PMID 27473595. S2CID 26307123.
  6. ^ a b Poblet, Enrique; Jiménez, Francisco; Ortega, Francisco (August 2004). "The contribution of the arrector pili muscle and sebaceous glands to the follicular unit structure". Journal of the American Academy of Dermatology. 51 (2): 217–222. doi:10.1016/j.jaad.2004.01.054. ISSN 0190-9622. PMID 15280840.
  7. ^ Journal of the American Academy of Dermatology Volume 51, Issue 2, August 2004, Pages 217-222 The contribution of the arrector pili muscle and sebaceous glands to the follicular unit structure☆ Enrique Poblet, Francisco Ortega.
  8. ^ Budhiraja, Virendra; Rastogi, Rakhi; Khare, Satyam; Khare, Anjali; Krishna, Arvind (2010-09-01). "Histopathological changes in the arrector pili muscle of normal appearing skin in leprosy patients". International Journal of Infectious Diseases. 14: e70–e72. doi:10.1016/j.ijid.2009.11.018. ISSN 1201-9712. PMID 20207571.