Freckle
For other uses of the word, see Freckles (disambiguation).
| Freckle | |
|---|---|
| Classification and external resources | |
 Facial freckles on a child. |
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| ICD-10 | L81.2 |
| MeSH | D008548 |
Freckles are clusters of concentrated melanin which are most often visible on people with a fair complexion. A freckle is also called an "ephelis". Freckles do not have an increased number of melanin producing cells (melanocytes). This is in contrast to lentigines and moles.[1]
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[edit] Biology
Freckles can be found on anyone no matter their genetic background; however, having freckles is genetic and is related to the presence of the dominant melanocortin-1 receptor MC1R gene variant.[2] The formation of freckles is triggered by exposure to sunlight. The exposure to UV-B radiation activates melanocytes to increase melanin production, which can cause freckles to become darker.
Freckles are predominantly found on the face, although they may appear on any skin exposed to the sun, such as the shoulders. Freckles are rare on infants, and more commonly found on children before puberty. Upon exposure to the sun, freckles will reappear if they have been altered with creams or lasers and not protected from the sun, but do fade with age in some cases. They can also be treated with citric acid.
Freckles are not a skin disorder, but people with freckles generally have a lower concentration of photoprotective melanin and are therefore more susceptible to the harmful effects of UV-radiation. It is suggested that they avoid overexposure and use sunscreen.[3][4]
[edit] Types of freckles
Ephelides is a genetic trait. It is used to describe a freckle which is flat, light brown or red, and fades in the winter. Ephelides are more common in those with light complexions, although they are found on people with a variety of skin tones. The regular use of sunblock can inhibit their development.
Liver spots (also known as sun spots and Lentigines) are freckles that may not fade in the winter. Rather, they form after years of exposure to the sun. Lentigines are more common in older people.
[edit] See also
[edit] References
- Notes
- ^ Robbins and Cotran Pathologic Basis of Disease Elsevier. 2005. Page 1232. ISBN 0808923021 .
- ^ Online 'Mendelian Inheritance in Man' (OMIM) 266300
- ^ Hanson Kerry M.; Gratton Enrico; Bardeen Christopher J. (2006). "Sunscreen enhancement of UV-induced reactive oxygen species in the skin". Free Radical Biology and Medicine 41 (8): 1205–12. doi:10.1016/j.freeradbiomed.2006.06.011. PMID 17015167.
- ^ Garland C, Garland F, Gorham E (1992). "Could sunscreens increase melanoma risk?". Am J Public Health 82 (4): 614–5. doi:10.2105/AJPH.82.4.614. PMC 1694089. PMID 1546792. http://www.ajph.org/cgi/reprint/82/4/614.
- Bibliography
- Millington GWM (2006). "Proopiomelanocortin (POMC): the cutaneous roles of its melanocortin products and receptors". Clin Exp Dermatol 31 (3): 407–412. doi:10.1111/j.1365-2230.2006.02128.x. PMID 16681590.
[edit] External links
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Wikimedia Commons has media related to: Freckles |
- MedicineNet.com: Freckles
- eMedicine: Ephelides (Freckles). Free subscription required.
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