Why do we Tan?

A portrait taken using only UV light between
the wavelengths of 335 and 365 nanometers.

Skin, the bodies' largest organ. Thick or thin, light, dark and everything in between, it is our primary defense against the environmental hazards we're exposed to every hour of every day. We know this. We know the dangers of unprotected and extended exposure to harmful UV rays, and yet many of us still risk it.

So, why do we tan? And I don't mean why do we go outside and lounge in the splendor of the sunshine. I mean why does our skin change color as a result? What exactly is going on at a cellular level to cause this change? And while we're on this topic, why does exposure to the sun lighten our hair?

Turns out it's all down to ultraviolet radiation, melanin and whether cells are alive or dead.

THE GOOD: Moderate exposure to the sun contributes to the production of vitamin D by the body.


THE BAD: Excessive exposure to ultraviolet rays has negative health effects, including sunburn and increased risk of skin cancer.[1]


THE UGLY: Overexposure to ultraviolet radiation is known to cause skin cancer,[2] make skin age and wrinkle faster,[3] mutate DNA,[4] and impair the immune system.[5] Frequent tanning bed use triples the risk of developing melanoma, the deadliest form of skin cancer.[6] 

Researchers at Stanford University School of Medicine have recently published findings linking skin cancer to ultraviolet light via damage caused to a gene involved in control of cell division.

THE OBSESSED: Though the mechanism by which tanning addiction occurs is unknown, some evidence indicates that the release of endorphins during the tanning process causes the pleasurable effects that underlie the addiction.[7] 

The International Agency for Research on Cancer places the use of tanning beds at the highest cancer risk category, describing them as carcinogenic to humans, if used as the manufacturer recommends. 

Tanning bed use under the age of 35 increases melanoma risk by 75%. (Source: skincancer.org)

The Electromagnetic Spectrum

Sunlight is a portion of the electromagnetic radiation given off by the Sun, in particular infrared, visible, and ultraviolet light. On Earth, sunlight is filtered through the Earth's atmosphere, particularly the ozone layer.[8]


Ultraviolet (UV) light, is electromagnetic radiation with a wavelength shorter than that of visible light but longer than X-rays (from 400 nm to 10 nm in wavelength).

Suntan and sunburn are familiar effects of over-exposure.

The ultraviolet frequencies responsible for tanning are often divided into the UVA and UVB ranges.

Melanin protects the body by absorbing solar radiation. It is produced by cells called melanocytes in a process called melanogenesis, which is the body's reaction to direct damage from UV radiation.[9] The body seeks to repair this damage and protect the skin by creating and releasing further melanin into the skin's cells. With the production of the melanin, the skin color darkens, but the UV-B in sunlight can also cause sunburn.

There are two different mechanisms involved in production of a tan by UV exposure:

Firstly, UV-A radiation creates oxidative stress, which in turn oxidises existing melanin and leads to its rapid darkening. Thus, the effect of UV-A leads to skin darkening, but the effect of this is mostly cosmetic and therefore offers little protection against UV-B and sunburn.[10] UV-A is blocked less than UV-B by many sunscreens, but is blocked to some degree by clothing.

In the second process, triggered primarily by UV-B, there is an increase in production of melanin. This leads to delayed tanning, and first becomes visible about 72 hours after exposure.[11] The tan that is created by increased melanogenesis lasts much longer than the one that is caused by oxidation of existing melanin, and does provide protection against UV skin damage and sunburn. UV-B is blocked by virtually all sunscreens in accordance with their SPF.

(Source: Wikipedia)



And, why does your hair turn blond?


The UV in sunlight bleaches (oxidizes into a colorless compound), and destroys the melanin in your hair, making it appear lighter. 

"Since hair is dead, the hair will stay that color until new hair comes in. ... This is why your hair gets lighter. Blond hair is really just colorless hair or hair with very little melanin in it." (Source: Dr. Aaron Shafer, Stanford University)

UPDATES / RELATED

Americans Are Still Pretty Confused About How Sunscreen Works: Survey / Medical Daily / June 17, 2015
Fact or Fiction?: A "Base Tan" Can Protect Against Sunburn / Scientific American / May 22, 2015 Woman's Skin Cancer Selfie Reveals Dangers Of Frequent Tanning, Need For Sunscreen / Medical Daily / May 13, 2015









REFERENCES

[1] http://www.cancer.org/cancer/cancercauses/radiationexposureandcancer/uvradiation/index
[2] "Reference Solar Spectral Irradiance: Air Mass 1.5".
[3] Hugo A. Tejeda, Antonello Bonci, Shedding “UV” Light on Endogenous Opioid Dependence, Cell, Volume 157, Issue 7, 19 June 2014, Pages 1500-1501, ISSN 0092-8674, http://dx.doi.org/10.1016/j.cell.2014.06.009. (http://www.sciencedirect.com/science/article/pii/S0092867414007302)
[4] https://www.ncbi.nlm.nih.gov/pubmed/20979596 Pigment Cell Melanoma Res. 2011 Feb;24(1):136-47. doi: 10.1111/j.1755-148X.2010.00764.x. Epub 2010 Oct 6. The deceptive nature of UVA tanning versus the modest protective effects of UVB tanning on human skin. Miyamura Y, et al. PMID 20979596
[5] Amy Thorlin (5 February 2006). articles/indoor_tanning/729_621feat2.html "The Tanning Process". Lookingfit.com.
[6] Nita Agar; Antony R. Young (2005). "Review: Melanogenesis: a photoprotective response to DNA damage?". Mutation Research/Fundamental and Molecular Mechanisms of Mutagenesis 571 (1–2): 121–132. doi:10.1016/j.mrfmmm.2004.11.016. PMID 15748643.
[7] "NTP: Report on Carcinogens (RoC)". Ntp.niehs.nih.gov. 13 February 2009. 

[8] Fisher GJ, Wang ZQ, Datta SC, Varani J, Kang S, Voorhees JJ (November 1997). "Pathophysiology of premature skin aging induced by ultraviolet light". N. Engl. J. Med. 337 (20): 1419–28. doi:10.1056/NEJM199711133372003. PMID 9358139.
[9] Sinha RP, Häder DP (April 2002). "UV-induced DNA damage and repair: a review". Photochem. Photobiol. Sci. 1 (4): 225–36. doi:10.1039/B201230H. PMID 12661961.
[10] Baadsgaard O (January 1991). "In vivo ultraviolet irradiation of human skin results in profound perturbation of the immune system. Relevance to ultraviolet-induced skin cancer" (PDF). Arch Dermatol 127 (1): 99–109. doi:10.1001/archderm.1991.01680010109019. PMID 1824747.
[11] Peeples, Lynne. Study: Frequent tanning-bed use triples melanoma risk. CNN. 27 May 2010.



SOURCES

http://kidshealth.org/parent/firstaid_safe/outdoor/sun_safety.html
http://genetics.thetech.org/ask/ask180
http://en.wikipedia.org/wiki/Electromagnetic_spectrum
http://en.wikipedia.org/wiki/Ultraviolet
http://en.wikipedia.org/wiki/Sunlight
http://www.sciencedaily.com/releases/2014/09/140907181722.htm?utm_source=feedburner
http://en.wikipedia.org/wiki/Sun_tanning

IMAGE CREDITS

"UV Portrait" by Spigget - Own work. Licensed under Creative Commons Attribution-Share Alike 3.0 via Wikimedia Commons - http://commons.wikimedia.org/wiki/File:UV_Portrait.jpg#mediaviewer/File:UV_Portrait.jpg


"Electromagnetic-Spectrum" by Victor Blacus - SVG version of File:Electromagnetic-Spectrum.png. Licensed under Creative Commons Attribution-Share Alike 3.0 via Wikimedia Commons - http://commons.wikimedia.org/wiki/File:Electromagnetic-Spectrum.svg#mediaviewer/File:Electromagnetic-Spectrum.svg