Tuesday, June 4, 2013

How Does It Work? Tanning

Unless you have literally never been outside (in which case I really hope you are drinking Vitamin D fortified milk), you are probably aware that being in the sun can cause a tan.

Although we are only just now beginning to elucidate the mechanisms of tanning, the dramatic increase in melanoma frequencies has made this an important issue of dermatological study. According to the Skin Cancer Foundation, the frequency of melanoma in women has increased 800% since 1970. This startling increase may be at least partially explained by use of tanning beds and by childhood sunburns accrued on family vacations. Now, I think, is the time to curse any loving family members who may have taken you to the beach.

DAMN YOU, CARING PARENTS.
The pigment associated with tanning is called melanin. Melanin absorbs UV light, protecting the skin. Because there are so many different molecular structures for various melanins, characterizing them has been a challenge for scientists. However, it clear that melanin is capable of absorbing all UV light, and its potential to absorb light decreases exponentially as you get closer and closer to the visible spectrum. Melanin has an estimated SPF of somewhere between 1.5 and 4. (This means that it is able to absorb somewhere 50 and 75% of UV rays). That's hardly a replacement for sunscreen, but clearly offers some protective effects. Additionally, melanin also may be able to form "caps" on top of the nucleus, reducing DNA damage caused by UV rays.

Melanin in pigmented melanoma
Source: http://en.wikipedia.org/wiki/File:Pigmented_melanoma_-_cytology.jpg
Unfortunately, melanin molecules are hardly an inert guards protecting your skin with diligence. Once exposed to light, they may degrade or produce free radicals. This lessens their effectiveness and may even prove to be damaging.

Merely knowing that melanin is the pigment of a golden tan is remarkably little knowledge. We can easily imagine a variety of ways that UV light could induce darker skin. Hypotheses have included the the stimulation of melanogenesis and changing the shape of the melanin. In the end, a 2005 study published in Nature by Tadokoro and colleagues showed it was neither!

Source: http://www.nature.com/jid/journal/v124/n6/fig_tab/5602865f5.html?url=/jid/journal/v124/n6/full/5602865a.html#figure-title

It appears that the main mechanism of action for tanning is the migration of melanin towards the surface of the skin, a process that occurs within one week of UV exposure. Normally, melanin would take closer to four weeks to migrate from the basal layer of skin to the surface.

Although we normally think of UVA light as the rays associated with tanning and UVB light as the rays associated with sunburns, there is evidence suggesting that a secondary tanning mechanism is caused by UVB light: melanogenesis. Indeed, these two mechanisms have been separated out by Miyamura and colleagues. They found that tanning induced by UVA light had no protective effect on DNA damage, but tanning induced by UVB light did have a slight protective effect. Because UVA light merely results in the rearrangement of pre-existing melanin, whereas UVB light stimulates melanin production, only the latter is capable of reducing DNA damage associated with sun exposure.

The silliest tan lines I have ever had. Always wear sunscreen, but if you wear a fishnet shirt to a Pride Parade, EXTRA wear sunscreen.
It is important to note, of course, that all UV exposure causes DNA and other cellular damage, leading to increases risks of skin cancer... so getting a "base tan" in UVB light is hardly an effective method of keeping your skin healthy. Furthermore, if you wanted to get your base tan in a tanning bed, you'd be especially shit out of luck. Tanning beds are 97% UVA, which, as shown in the Miyamura study, is not protective of DNA damage... All that the base tan would give you is a false sense of security.

6 comments:

  1. Haha, best tan lines ever! I have the dubious honour of never, ever tanning. My skin undergoes a lovely transition from lily white to lobster red (sometimes in five minutes flat), then peels and starts the process again.

    It makes me laugh when people are all "I'm tanned, I don't need sunscreen!". I spent a week at the beach with a friend who's half-Chinese and can seriously tan after ten minutes sun exposure. I came home pale as ever and she had a crimson back.Every time she winced I'd say "told you so!".

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    1. I'm exactly the same, pasty white burns to crimson, then I get about one day of tan before it starts to peel. After a week of peeling I'm back to white. I was unfortunate enough to get a blustering sunburn after a couple hours out on an overcast day a few years ago. My hair usually covers my neck, but I had it up that day and didn't think to put sunblock on. I'm sure if I get any cancerous spots later on, that's where they'll be. :( I'm pretty good with protecting whatever is exposed usually..

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  2. That was supposed to say blistering..

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    1. Have someone keep an eye on your neck! If anything happens, skin cancer is very treatable as long as it's caught early. Gives you a nasty scar, though...

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    2. I can back you up on that, Robyn. In December I had a suspicious mole removed and it turned into a whole ordeal. Now I have an enormous and silly looking scar on my arm. Unfortunately, my Swedish heritage somehow managed to overpower my Cuban heritage so I'm lily white and very burnable.

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  3. My mom had a dark spot on her upper neck / jawline for decades. I saw her a couple summers ago and said "Hey, that thing on your neck looks darker," and she said "Really? I hadn't noticed, I'll have it checked out though, thanks."

    It was melanoma in situ. Fortunately she caught it while it was still in situ and only had to have a chunk of skin about half the size of a dollar bill removed and is now cancer free with no further treatment, but the thought of what would have happened if I hadn't said anything makes me ill.

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