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Author Topic: Is it true that our skins tan, because of Ultra Violet light?  (Read 5143 times)

Offline Seany

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UV light is what causes our skins to tan..?


 

Offline Andrew K Fletcher

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Is it true that our skins tan, because of Ultra Violet light?
« Reply #1 on: 03/09/2007 13:12:01 »
Another source of tannin is tea and coffee in our diet, concentrated in the skin by evaporation from the sun and the wind. This tannin in the skin can be observed when sweating in bed as the tannin is excreted in the sweat staining the sheets and mattress. I suspect that additional oxidization of the fluids at the surface of the skin may play a part also.

How else can the colour of a new born babies skin be explained when in the case of a native African baby for example has never been in contact with the sun, yet shows evidence of darkened skin tone. Food for thought?
 

another_someone

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Is it true that our skins tan, because of Ultra Violet light?
« Reply #2 on: 03/09/2007 13:13:59 »
Yes, but I believe it is more low energy UV light rather than the shorter wavelength high energy UV light.  Since tanning is supposed to protect us from the harmful effects of an excess of UV light, it is perfectly reasonable that it should be triggered by UV light.
 

another_someone

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Is it true that our skins tan, because of Ultra Violet light?
« Reply #3 on: 03/09/2007 13:26:39 »
Another source of tannin is tea and coffee in our diet, concentrated in the skin by evaporation from the sun and the wind. This tannin in the skin can be observed when sweating in bed as the tannin is excreted in the sweat staining the sheets and mattress. I suspect that additional oxidization of the fluids at the surface of the skin may play a part also.

How else can the colour of a new born babies skin be explained when in the case of a native African baby for example has never been in contact with the sun, yet shows evidence of darkened skin tone. Food for thought?


Tannin has nothing to do with melanin (which is the substance that causes the skin to tan - even in native African babies who have never been exposed to the sun).
 

Offline Seany

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Is it true that our skins tan, because of Ultra Violet light?
« Reply #4 on: 03/09/2007 13:27:18 »
Are people with darker skin colours more resistent to having skin cancer?
 

Offline Seany

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Is it true that our skins tan, because of Ultra Violet light?
« Reply #5 on: 03/09/2007 13:28:21 »
I heard that melanin is what causes are skin to tan.. But there is no way of taking melanin out, for people who want their skins to whiten?

Like a cream or lotion which removes melanin or such.
 

another_someone

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Is it true that our skins tan, because of Ultra Violet light?
« Reply #6 on: 03/09/2007 13:31:00 »
Are people with darker skin colours more resistent to having skin cancer?

Yes - pure and simple (but they are more susceptible to rickets, and other problems with vitamin D deficiency, in countries with less sunlight).
 

Offline Seany

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Is it true that our skins tan, because of Ultra Violet light?
« Reply #7 on: 03/09/2007 13:37:16 »
Oh.. But if their skins are darker.. Don't they absorb more sunlight, thus more vitamin D?
 

another_someone

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Is it true that our skins tan, because of Ultra Violet light?
« Reply #8 on: 03/09/2007 13:43:18 »
I heard that melanin is what causes are skin to tan.. But there is no way of taking melanin out, for people who want their skins to whiten?

Like a cream or lotion which removes melanin or such.

I don't think there is a safe way of doing it (although I suspect there may be chemicals you could use to whiten the skin, but I don't think they are safe).

The most common ways of whitening the skin have either been to use an external layer of white pigment over the skin, or simply to avoid exposure to the sun (hence the totally enveloping Arab dress).
 

another_someone

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Is it true that our skins tan, because of Ultra Violet light?
« Reply #9 on: 03/09/2007 13:43:56 »
Oh.. But if their skins are darker.. Don't they absorb more sunlight, thus more vitamin D?

No - the absorption is not in the right way.

There is good clinical evidence that people of darker skin are more likely to suffer from vitamin D deficiency in higher latitudes.
« Last Edit: 03/09/2007 13:45:38 by another_someone »
 

Offline Seany

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Is it true that our skins tan, because of Ultra Violet light?
« Reply #10 on: 03/09/2007 13:45:47 »
I heard that melanin is what causes are skin to tan.. But there is no way of taking melanin out, for people who want their skins to whiten?

Like a cream or lotion which removes melanin or such.

I don't think there is a safe way of doing it (although I suspect there may be chemicals you could use to whiten the skin, but I don't think they are safe).

The most common ways of whitening the skin have either been to use an external layer of white pigment over the skin, or simply to avoid exposure to the sun (hence the totally enveloping Arab dress).

So how come we whiten when not in the sun anymore?
 

Offline Andrew K Fletcher

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Is it true that our skins tan, because of Ultra Violet light?
« Reply #11 on: 03/09/2007 14:38:40 »
beta-carotene has nothing to do with melanin either, yet can turn a babies skin bright orange, thus proving that tannin can also migrate to the skin.

He takes a bow and anticipates a little back peddling
 

another_someone

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Is it true that our skins tan, because of Ultra Violet light?
« Reply #12 on: 03/09/2007 15:30:08 »
beta-carotene has nothing to do with melanin either, yet can turn a babies skin bright orange, thus proving that tannin can also migrate to the skin.

He takes a bow and anticipates a little back peddling

I did not say that tannin could never get to the skin, but I would suggest that if you have enough tannin in you to show up in the skin (the same is true of beta carotene), then you have a problem, hence this is not what normally causes tanning in a live human skin (in dead skin, tannin is used by the tanning industry to make leather, but it is the astringency of the substance that is more important than its colour rendition - if you want to turn your skin to leather, then tannin may well be the way to go).
 

another_someone

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Is it true that our skins tan, because of Ultra Violet light?
« Reply #13 on: 04/09/2007 01:16:58 »
So how come we whiten when not in the sun anymore?

Are you asking what the process is, or what the reason is.

The reason, as indicated above, is there is a trade-off between too much sun (skin cancer, and possibly excessive breakdown of folic acid), and too little sunlight (vitamin D deficiency), so the body tries to regulate the amount of sunlight that penetrates the skin by varying the amount of melenin in the skin.  The problem is that the human skin is capable of some adjustment in this area, but it is only limited variability, so over the generations people who have grown up in countries with large amounts of sunlight have genes that give a large base value for melanin in their skin (and some small variability within that), while people who have developed in countries with less sunlight have developed genes with a low base level of melanin in their skin, and some variation upon that.

It is not clear whether humans originally had black or white skins - there seem to be arguments for both (or maybe they passed through variations from white to black, and then some of them back to white).  Before humans lost most of their body hair, the melanin in the hair was sufficient to protect the skin beneath (as is the case for the other apes).
 

Offline _Stefan_

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Is it true that our skins tan, because of Ultra Violet light?
« Reply #14 on: 04/09/2007 07:45:44 »
In that case, what is the colour of a chimp's skin if you shave the fur off?
 

another_someone

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Is it true that our skins tan, because of Ultra Violet light?
« Reply #15 on: 04/09/2007 12:21:23 »
In that case, what is the colour of a chimp's skin if you shave the fur off?

http://en.wikipedia.org/wiki/Human_skin_color
Quote
In considering the tone of human skin in the long span of human evolution, Jablonski and Chaplin note that there is no empirical evidence to suggest that the human ancestors six million years ago had a skin tone different from the skin tone of today's chimpanzees—namely light-skinned under black hair.

http://www.e-ijd.org/article.asp?issn=0019-5154;year=2007;volume=52;issue=2;spage=71;epage=77;aulast=Radhakrishnan
Quote
The present article reviews various evolutionary events that resulted in skin color variation among humans. Skin of the early man is presumed to be colorless as that of the chimpanzees.

http://www.britannica.com/eb/article-9024115/chimpanzee
Quote
Chimpanzees are covered by a coat of brown or black hair, but their faces are bare except for a short white beard. Skin colour is generally white except for the face, hands, and feet, which are black. The faces of younger animals may be pinkish or whitish. Among older males and females, the forehead often becomes bald and the back becomes gray.

But by contrast, Gorillas:

http://www.torontozoo.com/animals/details.asp?AnimalId=352
Quote
Skin/Color/Coat: The colour of the coat varies considerably, ranging through black, silver and shades of red. Black is more usual. The skin is also black. As a male gorilla reaches physical maturity (between 12 and 15 years of age), he develops his silvery grey colouration. Old males often lack chest hair. The face, ears, palms and soles of feet are bare.
 

Offline Bored chemist

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Is it true that our skins tan, because of Ultra Violet light?
« Reply #16 on: 04/09/2007 22:01:04 »
"Another source of tannin is tea and coffee in our diet, concentrated in the skin by evaporation from the sun and the wind. This tannin in the skin can be observed when sweating in bed as the tannin is excreted in the sweat staining the sheets and mattress. I suspect that additional oxidization of the fluids at the surface of the skin may play a part also."

B********!

I have seen some rubbish in my time but that's a classic.
The melanin that forms in skin, hair and the iris of the eye is formed from the amino acid tyrosine. It has nitrogen in it.
Tannins are fromed from (mainly) gallic acid, in combination with sugars and other things. It does not contain nitrogen.
More or less the defining property of tannins is that they bind to proteins. Since people are basically wet fatty protein it's hard to see how the tannin could diffuse through them from the gut to the skin rather than reacting with a protein along the way.
Actually, it's worse than that- the tannins are not generally very soluble and they are also pretty indigestible. They may contribute to the colour of excreta but that's a different question. The only readilly digestible ones are things like epicatachin and gallotannin. These compounds are not coloured- any colour there is due to impurities.
Here's more stuff about tannins than you ever need to know.
http://www.users.muohio.edu/hagermae/tannin.pdf

The absorption of light by the melanin in the skin (whether that's a tan or normal skin pigmentation) prevents the light getting deep into the tissues where it can produce vitamin D.
« Last Edit: 05/09/2007 20:31:31 by Bored chemist »
 

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Is it true that our skins tan, because of Ultra Violet light?
« Reply #16 on: 04/09/2007 22:01:04 »

 

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