Editing Melanocytic nevus (section)

==Cause==
The cause of this condition is not clearly understood, but it is thought to result from a defect in [[embryologic development]] during the first 12 weeks of pregnancy. The defect is thought to cause a proliferation of [[Melanocyte|melanocytes]], the cells responsible for normal skin color. When melanocytes are produced at an extremely rapid rate, they form in clusters instead of spreading out evenly, resulting in abnormal skin pigmentation in some areas of the body.{{Cn|date=June 2024}}

===Genetics===
[[Genes]] can influence a person's moles.

[[Dysplastic nevus syndrome]] is a largely [[hereditary]] condition that causes a person to have a large quantity of moles (often 100 or more), with some larger than normal or atypical. This often leads to a higher risk of [[melanoma]], a serious type of [[skin cancer]].<ref>{{cite journal|author=Burkhart CG|title=Dysplastic nevus declassified: even the NIH recommends elimination of confusing terminology|journal=Skinmed|volume=2|issue=1|pages=12–13|year=2003|pmid=14673319|doi=10.1111/j.1540-9740.2003.01724.x}}</ref> Dysplastic nevi are more likely than ordinary moles to become cancerous. While dysplastic nevi are common and many people have a few of these abnormal moles, having more than 50 ordinary moles also increases the risk of developing melanoma.<ref name="ncimelanoma">{{cite web|url=http://www.nci.nih.gov/cancertopics/wyntk/melanoma/page7|title=What You Need To Know About Melanoma - Melanoma: Who's at Risk?|date=January 1980|access-date=2008-05-18|publisher=[[National Cancer Institute]]}}</ref>

In the general population, a slight majority of melanomas do not form in existing moles but rather create new [[tumour|growths]] on the skin. Somewhat surprisingly, this pattern also applies to those with dysplastic nevi. These individuals are at a higher risk of melanoma occurring not only where there is an existing mole but also in areas without moles.<ref>{{cite journal|vauthors=Pope DJ, Sorahan T, Marsden JR, Ball PM, Grimley RP, Peck IM |title=Benign pigmented nevi in children. Prevalence and associated factors: the West Midlands, United Kingdom Mole Study|journal=Arch Dermatol|volume=128|issue=9|pages=1201–1206|year= 1992|pmid=1519934|doi=10.1001/archderm.128.9.1201}}</ref><ref>{{cite journal|vauthors=Goldgar DE, Cannon-Albright LA, Meyer LJ, Piepkorn MW, Zone JJ, Skolnick MH |title=Inheritance of nevus number and size in melanoma and dysplastic nevus syndrome kindreds|journal=J. Natl. Cancer Inst.|volume=83|issue=23|pages=1726–1733|year=1991|pmid=1770551|doi=10.1093/jnci/83.23.1726}}</ref> Consequently, such persons need regular examinations to check for changes in their moles and to identify any new ones.

===Sunlight===
[[Ultraviolet]] (UV) light from the sun causes premature aging of the skin and skin damage that can lead to melanoma. Researchers hypothesized that overexposure to UV, including excessive sunlight, may play a role in the formation of acquired moles.<ref>{{cite journal |vauthors=van Schanke A, van Venrooij GM, Jongsma MJ, etal |title=Induction of nevi and skin tumors in Ink4a/Arf Xpa knockout mice by neonatal, intermittent, or chronic UVB exposures|journal=Cancer Res. |volume=66|issue=5|pages=2608–2615|year=2006|pmid=16510579|doi=10.1158/0008-5472.CAN-05-2476|hdl=10029/7145 |url= http://cancerres.aacrjournals.org/cgi/pmidlookup?view=long&pmid=16510579|doi-access=free|hdl-access=free}}</ref> However, more research is needed to determine the complex interaction between genetic makeup and overall UV exposure. Some strong indications supporting this hypothesis (but falling short of proof) include:
*The relative lack of moles on the buttocks of people with dysplastic nevi
*The known influence of sunlight on [[freckle]]s (spots of melanin on the skin, distinct from moles)

Studies have found that sunburns and excessive sun exposure can increase risk factors for melanoma. This is in addition to the higher risk already faced by individuals with dysplastic nevi (the uncertainty is in regards to acquiring benign moles). To prevent and reduce the risk of melanoma caused by UV radiation, the [[American Academy of Dermatology]] and the [[National Cancer Institute]] recommend:

* Staying out of the sun between 10 a.m. and 4 p.m. standard time (or whenever one's shadow is shorter than one's height)
* Wearing long sleeves and trousers
* Wearing hats with a wide brim
* Applying sunscreens
* Wearing sunglasses that have UV-deflecting lenses<ref name="ncimelanoma" />