Editing Callus (section)

==Cause==
Normally, a callus will form on any part of the skin exposed to excess friction over a long period of time. Activities that are known for causing calluses include [[list of construction trades|construction work]] and craftwork, [[the arts]],<ref>{{Cite journal |last1=Sims |first1=Susan E. G. |last2=Engel |first2=Laura |last3=Hammert |first3=Warren C. |last4=Elfar |first4=John C. |date=2015-08-05 |title=Hand Sensibility, Strength, and Laxity of High-Level Musicians Compared to Non- Musicians |journal=The Journal of Hand Surgery |volume=40 |issue=10 |pages= 1996–2002.e5|doi=10.1016/j.jhsa.2015.06.009 |issn=0363-5023 |pmc=4584184 |pmid=26253604}}</ref> [[food preparation]], many [[sports]] and [[physical activities]],<ref>{{Cite journal |last1=Grima |first1=Joseph N. |last2=Vella Wood |first2=Michelle |last3=Portelli |first3=Nadia |last4=Grima-Cornish |first4=James N. |last5=Attard |first5=Daphne |last6=Gatt |first6=Alfred |last7=Formosa |first7=Cynthia |last8=Cerasola |first8=Dario |date=2022-01-05 |title=Blisters and Calluses from Rowing: Prevalence, Perceptions and Pain Tolerance |journal=Medicina |volume=58 |issue=1 |pages=77 |doi=10.3390/medicina58010077 |issn=1010-660X |pmc=8779584 |pmid=35056385|doi-access=free }}</ref><ref>{{Cite journal |last1=Emer |first1=Jason |last2=Sivek |first2=Rachel |last3=Marciniak |first3=Brian |date=2015-04-08 |title=Sports Dermatology: Part 1 of 2 Traumatic or Mechanical Injuries, Inflammatory Conditions, and Exacerbations of Pre-existing Conditions |journal=The Journal of Clinical and Aesthetic Dermatology |volume=8 |issue=4 |pages= 31–43|issn=1941-2789 |pmc=4456799 |pmid=26060516}}</ref> and fashion choices like wearing [[high heels]].<ref>{{Cite web |last=Bouchez |first=Colette |date=2009-02-09 |editor-last=Chang |editor-first=Louise |title=Tips to Avoid Foot Pain From High Heels |url=https://www.webmd.com/women/features/tips-to-avoid-foot-pain-from-high-heels |access-date=2022-03-10 |website=[[WebMD]] |language=en}}</ref>

Although calluses can occur anywhere on the body as a reaction to moderate, constant "grinding" pressure, they are most  often found on the [[foot]] (where the most pressure and friction are applied). On the feet (arguably the source of the most problematic calluses), they typically form on the metatarsal-phalangeal joint area ("balls of the foot"), heels and small toes due to the compression applied by tightly fitting shoes.

Biologically, calluses are formed by the accumulation of [[cellular differentiation|terminally]] differentiated [[keratinocyte]]s in the outermost layer of skin. Though the cells of calluses are dead, they are quite resistant to mechanical and chemical damage due to extensive networks of cross-linked proteins and [[Hydrophobe|hydrophobic]] keratin [[intermediate filaments]] containing many [[disulfide bonds]].<ref>{{cite journal |vauthors=Tantisiriwat N, Janchai S |title=Transglutaminases: multifunctional cross-linking enzymes that stabilize tissues. |journal=The FASEB Journal |volume=5 |issue=15 |pages=3071–7 |date=Dec 1991 |doi=10.1096/fasebj.5.15.1683845 |pmid=1683845 |s2cid=6751428 |url=http://www.fasebj.org/content/5/15/3071.long|doi-access=free |url-access=subscription }}</ref> It is the natural reaction of the [[Anatomical terms of location#Hands and arms|palmar]] or [[plantar]] skin. Too much friction occurring too fast for the skin to develop a protective callus will cause a [[blister]] or [[abrasion (medical)|abrasion]] instead.

Sometimes a callus occurs where there is no rubbing or pressure. These [[hyperkeratoses]] can have a variety of causes. Some toxic materials, such as [[arsenic]], can cause thick palms and soles. Some diseases, such as [[syphilis]], can cause thickening of the palms and soles as well as pinpoint hyperkeratoses. There is a benign condition called ''keratosis palmaris et plantaris'', which produces corns in the creases of the fingers and non-weight bearing spaces of the feet. Some of this may be caused by [[actinic keratosis]], which occurs due to overexposure to sun or with age and hormonal shifts.

===Corns===
{{Main|Corn (pathology)}}
[[Image:Corns.jpg|thumb|Painful corns]]

A [[corn (pathology)|corn]] (or ''clavus'', plural ''clavi'') is a cone-shaped callus that penetrates into the dermis, usually on the feet or hands. Corns may form due to chronic pressure or rubbing at a pressure point (in this skin over a bone), or due to scar tissue from a healing wound creating pressure in a weight-bearing area such as the sole of the foot. If there is constant stimulation of the tissue producing the corns, even after the corn is surgically removed, the skin may continue to grow as a corn.<ref name=":0">{{Cite web |title=Corns and Calluses: Symptoms, Treatment & Care Tips |url=https://my.clevelandclinic.org/health/diseases/16896-corns-and-calluses |access-date=2022-03-10 |website=[[Cleveland Clinic]]}}</ref>

The hard part at the center of the corn resembles a funnel with a broad raised top and a pointed bottom. Because of their shape, corns intensify the pressure at the tip and can cause deep tissue damage and [[Ulcer (dermatology)|ulceration]].<ref>{{Cite journal |last=Silverberg |first=Nanette B. |date=2019 |title=Corns (Clavus): Background, Pathophysiology, Etiology |url=https://emedicine.medscape.com/article/1089807-overview |journal=[[Medscape]] |url-access=registration}}</ref> The scientific name for a corn is ''heloma'' (plural ''helomata''). A hard corn is called a ''heloma durum'', while a soft corn is called a ''heloma molle''.

The location of the soft corns tends to differ from that of hard corns. Hard corns occur on dry, flat surfaces of skin. Soft corns (frequently found between adjacent toes) stay moist, keeping the surrounding skin soft. The corn's center is not soft however, but [[Induration|indurated]].

The specific diagnostic workup and treatments for corns may differ substantially from other forms of calluses.