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Author Topic: Why does dark pigment in the skin protect us from the sun?  (Read 11144 times)

Offline John Chapman

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We all know that dark colours absorb heat & light while light colours reflect them. It seems counterintuitive, therefore, that the pigment melanin darkens the skin. It would seem to make more sense if Caucasians evolved their skin colour in hot parts of the world while Negros developed their colour in less sunny areas to maximise sun absorption. How does melanin work? Is the colour incidental?


 

Offline Chemistry4me

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Offline John Chapman

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Why does dark pigment in the skin protect us from the sun?
« Reply #2 on: 18/02/2009 08:21:45 »
eh?
 

Offline Chemistry4me

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Why does dark pigment in the skin protect us from the sun?
« Reply #3 on: 18/02/2009 08:25:22 »
No luck with the link?
 

Offline John Chapman

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Why does dark pigment in the skin protect us from the sun?
« Reply #4 on: 18/02/2009 08:31:54 »
I've just found this post by Chris Smith in respect of a Question of the Week back in Jan 2004 which was about sunscreen:

Quote from: Chris on 11/06/2004
UV radiation is dangerous because it can damage DNA in skin cells, potentially triggering skin cancer. The skin responds to UV exposure by increasing the production of the dark pigment melanin, which is secreted into the skin by a population of cells called melanocytes. Melanin absorbs UV very efficiently, preventing further UV radiation from reaching the nucleated (DNA-containing) cells deeper in the skin, and hence preventing DNA damage.

This confirms that melanin absorbs UV in the surface of the skin before it goes deep enough to do any damage. Is that the full answer? It still seems counterintuitive.
 

Offline John Chapman

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Why does dark pigment in the skin protect us from the sun?
« Reply #5 on: 18/02/2009 08:34:13 »
Sorry Chem4me

I didn't realise it was a link. It just shows up as a one-word reply on my pc. I'll have a look now.
 

Offline John Chapman

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Why does dark pigment in the skin protect us from the sun?
« Reply #6 on: 18/02/2009 08:46:13 »
Chem4me's Wiki link:

Quote from: Wikipedia
The photochemical properties of melanin make it an excellent photoprotectant. It absorbs harmful UV-radiation and transforms the energy into harmless amounts of heat through a process called "ultrafast internal conversion". This property enables melanin to dissipate more than 99.9% of the absorbed UV radiation as heat[3] and it keeps the generation of free radicals at a minimum (see photoprotection). This prevents the indirect DNA damage which is responsible for the formation of malignant melanoma.

Similar to what Chris said and I suppose that must be the full answer. It just seems a long way round to achieve the end result. Why evolve a mechanism and then expend all that energy each time to absorb UV which is highly damaging instead of reflecting it away? I suppose if white skin doesn't naturally reflect UV then some defensive mechanism has to be evolved and melanin is as good as any!
 

Offline Chemistry4me

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Why does dark pigment in the skin protect us from the sun?
« Reply #7 on: 18/02/2009 08:58:31 »
Yep! :)
 

Offline Madidus_Scientia

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Why does dark pigment in the skin protect us from the sun?
« Reply #8 on: 18/02/2009 21:38:24 »
White skin would probably still absorb alot of UV radiation even if it did reflect most. Or maybe it doesn't reflect much UV light at all, only visible light.
 

Offline Chemistry4me

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Why does dark pigment in the skin protect us from the sun?
« Reply #9 on: 19/02/2009 07:35:41 »
You should start a new thread :)
 

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Why does dark pigment in the skin protect us from the sun?
« Reply #9 on: 19/02/2009 07:35:41 »

 

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