Tanning, either by the sun or by artificial means, is hugely popular in the United States and elsewhere. The word itself is interesting, deriving from the Old English tannian which in turn is derived from the Latin tannum, meaning oak bark. This makes sense, because the inner bark of certain oaks are rich in phenolic compounds that have been and still are used to tan raw skins into leather.
During the tanning process the skins darken, just like the human skin usually darkens when exposed to the ultraviolet light in sunlight or tanning salons. I use the term usually because some very fair people never tan but just burn, and very dark skinned people show little or no tanning. Albinos are not capable of tanning.
Before we get to the science behind tanning, it is of service to look at the cultural aspects of it. There has been a sea change in attitudes about tanning in the past century. I shall use my mum as an example.
My mum was born in 1921 in rural Arkansas. When she was a girl, the Great Depression struck and she and my grandparents had to work hard on the farm. In addition to their garden and animals, they raised cotton as a cash crop. Raising cotton by hand and without chemicals is brutal work. It has to be hoed, usually in the hottest part of the summer. It also has to be picked in early fall when it is still hot. Finally, after picking, the stalks have to be chopped to get ready for next season.
Despite all of this, my mum covered herself from head to toe, including her hands with gloves and head and face with a large bonnet. The reason? A suntan was a mark of being poor and lower class, forced to work out of doors rather than middle or upper class who worked inside. As a result, in her younger life she never had a tan at all. For reasons to be explained later, that was probably a good thing.
Attitudes slowly began to change when it was discovered that exposure to sunlight caused the production of Vitamin D in the skin, and Vitamin D is critical for a whole host of biological processes. Tanning became faddish in Europe and slowly spread to the US. In the 1940's tanning was becoming popular in the US, and in 1953 the Coppertone girl was introduced, a logo still used to this day with minor modification to fit modern norms. Here is a picture of the original logo:
In the 1960's and 1970's tanning was pretty much universal, but as medical evidence began to accumulate it was found that tanning involves much more than a bronzed look and lots of Vitamin D. It was found that tanning has many negative effects, including wrinkled skin, skin cancer of at least two types, age spots, immune system compromise, cataracts, and macular degeneration. We shall look at this after we explain the biology of tanning.
First, there are three divisions of ultraviolet light (UV). UV is light of frequency lower than 400 nanometers and longer than longer than 10 nm where the X-ray spectrum begins. UVA has wavelengths betwixt 400 and 315 nm, UVB betwixt 315 and 280 nm, and UVC from 280 down to 10 nm. For tanning purposes UVC is not relevant because it is strongly absorbed by the ozone layer and almost none reaches the surface of the earth. It is also filtered out of the emissions from tanning salon lamps.
Both UVA and UVB are responsible for tanning (by different mechanisms) and skin damage. A tan is the result of the release of existing melanin, the dark pigment or production of additional melanin. Melanin is produced by cells called, not surprisingly, melanocytes. UVA only causes the release of existing melanin, not the production of more. It also causes oxidation of a paler form of it to a darker form. UVB actually causes melanocytes to produce more melanin, so to get a really dark tan it is essential to have some UVB in the radiation.
Radiation is the key term, because a suntan is a direct result of radiation damage to the skin. Since both UVA and UVB can damage DNA (UVA indirectly, UVB directly), the body has evolved a mechanism to reduce exposure of cells to UV, and that is tanning. It turns out that the dark variety of melanin absorbs both UVA and UVB, thus providing some protection to cells beneath it. However, the absorption is not complete. Some UV still penetrates even a heavy tan.
Some people are under the mistaken impression that UVA is harmless. This is far from the case, and in some ways it may be more harmful than the more energetic UVB. First, UVA penetrates into the skin more deeply than UVB, affecting a greater number of cells. And since it does not cause sunburn, it is possible to get a LOT of UVA exposure with little apparent effect except for a mild tan. More on this later.
UVA damages DNA by a process called photooxidation, where reactive intermediates are produced in materials in the cell other than DNA, and these reactive intermediates then damage the DNA. These are usually single strand breaks and are responsible for much of the malignant melanoma from exposure. Because the reactive intermediates produced, it is UVA that is largely responsible for decreasing the immune system of the body as a whole. This reduction in immune activity can be responsible itself for increases in other types of cancer. This explains the evidence showing that people who use sunscreen seem to have an INCREASED risk for melanoma than people who do not use sunscreen at all.
How is that? Remember, sun burn is caused by UVB. Until very recently, sunscreens were rated only on how well they absorb UVB with no regard to UVA. In addition, there are more materials safe to apply to skin that filter UVB than for UVA, so many sunscreens allow essentially ALL of the UVA to penetrate the skin but since no UVB does, there is no sunburn, no pain, and a general feeling that all is well. However, what is really happening is that people who wear sunscreen just increase their exposure to harmful UVA. Sunscreen can thus actually do more harm than good! Most people self limit their exposure to the sun when they know that they will burn, and have a false sense of security when wearing sunscreen.
Some newer sunscreens DO block UVA. You have to look on the label and make sure that the product is certified to block both UVA and UVB, sometimes called "broad spectrum" sunscreens. Also, since UVB is what makes Vitamin D, you get essentially none of it when wearing a sunscreen, so Vitamin D deficiency is a real possibility. By the way, Americans are already on the low side for adequate Vitamin D intake.
UVB acts in a completely different manner. This has a personal connexion for me, and we are going to get Geeky. In graduate school I worked with a class of compounds called alpha,beta unsaturated ketones, or simply enones. For those of you who do not know, I am a physical chemist rather than a synthetic chemist. I took things (for the most part) that were available commercially and irradiated them with UVB to see what happened. You will have to put up with my hand sketches of some of my work. As you can see, my handwriting is still not fully recovered from my wrist condition.
This equation is read thusly:
Two molecules of cyclohex-2-ene-1-one when exposed to UVB radiation form cyclobutane dimers, one the so called "head to tail" dimer and the other the "head to Head" one.
What does this have to do with sunburn? Thymine is one of the four bases that carry information in DNA. If you look closely, you will see that it shares with the enone above a carbon doubly bonded to an oxygen with another double bond in the ring. When exposed to UVB, thymines close enough to each other can undergo the exact same reaction. Here is the formula for thymine:
Here is the formula for the cyclobutane dimer:
Because of geometrical considerations, only the head to head dimer can form. When these dimers form, a cascade of activity takes place in the amazing machine called the human body. The body actually recognizes the formation of these dimers because it changes the shape of the DNA containing then. Enzymes are expressed that can "clip" the DNA that contains the dimer and replace it with "new" DNA. Remember, the other strand of the DNA carries the same information, so there is a backup copy. However, this is not a perfect system and sometimes the DNA becomes corrupted, and sometimes this leads to cancer. The formation of these dimers also triggers the melanocytes to produce additional melanin, and that is why a UVB tan is darker than a UVA one.
UV damage to the eye can involve short term exposure that essentially sunburns the conjunctiva and the corneae. The most common natural cause is reflection of bright sunlight from snow (snow blindness). It also is not uncommon in welders with less than adequate lens darkness. It has occurred in tanning salons, and it is essential to wear proper eye protection there. In general the condition resolves itself after a number of painful days.
Longer term injury to the eye from UV is caused by irreversible photochemical reactions to the lens or lens capsule, causing them to become opaque. This condition is called cataracts, and is now generally treated surgically. When I was doing photochemical work, I always wore welder's glasses when the lamps were operating. I also decorated my laboratory with lots of blacklight posters!
Sometimes it is beneficial for a few medical conditions to expose the skin to UV, but for most people there is, aside from Vitamin D production, for UV exposure. Just to expose oneself to high levels of UV for purely cosmetic reasons borders on the irrational! Some studies suggest that melanoma rates are three times average for heavy users. This is a particularly nasty form of skin cancer because it tends to metastasize readily, unlike other skin cancers, and often invades the brain.
All of this information applies equally to natural sunlight and to tanning salons with a single exception. Tanning salon exposure is like sunlight on steroids! The mix of UVA/UVB is about the same from both sources (around 97:3), but the intensity in a salon can be up to 15 times that of the noon sun. Thus, those 20 minutes in the booth can be similar to FIVE HOURS of direct noon sun. In my opinion, this is just not safe.
Now for the part about my mum being wise to stay covered when she was young. Studies show that people under 30 or so are more sensitive to the negative effects of UV (both A and B), and the younger the more sensitive. It is unclear as to the reason for that, but it is known. Since she waited until later in life to uncover, she was spared much of the damage that others had. Even in her seventies, she did not have any age spots and just very light wrinkles on her face.
Once again, I do not give medical advice of any kind, but rather tell people what I do or do not do, and what I would or would not do if circumstances change. I do not avoid the sun completely. However, I do not intentionally expose my body to it for cosmetic reasons. When it is sunny, even in winter, I wear a broad brimmed hat. (My paternal grandfather looked like a Vulcan where they clipped his ear lobes to treat skin cancer caused by decades of overexposure.) When I am outdoors I try to stay out of direct sun as much as possible, but if I need to mow the lawn, I mow the lawn.
I avoid as much as possible exposure to the sun from 10 AM to 2 PM (standard time) when UV levels are highest. I do NOT use sunscreen since it is only protective for UVB unless specially formulated. The natural reddening of the skin from UVB exposure is my warning that it is time to get out of the sun. I NEVER have been to nor will I go to a tanning salon, and I have a dear friend who just started. She is young and feels poorly after she is done with her sessions. Perhaps she will reconsider after she reads this, and she knows that I wrote it especially for her.
I wear shorts and short sleeved shirts when it is hot. A little sun exposure is not a bad thing, because our reparative systems have evolved to accommodate that, and I like Vitamin D. If I were to be required to be in the sun for extended periods to times, I would procure a sunscreen that protects against both UVA amd UVB and apply it liberally. Parents, those of you applying a conventional sunscreen to your little ones thinking that you are doing the right thing, think again! You are exposing them to way more UVA than they should ever get. MAKE SURE THAT THE SUNSCREEN THAT YOU USE BLOCKS BOTH!
As far as esthetics go, tans do not personally turn me on, so to speak. I believe that people are attractive for reasons very much removed from the tint of their skin. Young people, listen up! Your bronze color may well mean that you will have severe wrinkles and age spots decades before you should. Is a little, fleeting color worth it?
In summary, the sun is not something to be avoided completely unless a special medical condition is present. On the other hand, too much UV exposure (and there is a very fine line betwixt OK and too much) should be avoided. Cosmetic reasons are a poor reason for skin damage.
Well, you have done it again! You have wasted many more einsteins of perfectly good photons reading this colorless piece. And even though Mike Huckabee realizes that his snarky opening commentary on his show on the Fox "News" Channel tonight was not funny when he reads me say it, I always learn much more than I could possibly hope to teach by writing this series. Thus, please keep those comments, questions, corrections and other feedback coming! Tips and recs are also always very welcome.
I shall stay around tonight as long as comments warrant, and shall return tomorrow evening around 9:00 for Review Time. Remember, no science or technology issue is off topic here, so feel free to talk about whatever is on your mind.
On a personal note, my wrist continues to improve rapidly. The only time that I wear the splint is when I type (it is difficult to hold my hand up for extended periods of time) and when I sleep to keep my wrist in neutral position. I continue to take the anti inflammatory drugs and supplements, and can see the light at the end of the tunnel. I am typing pretty much normally now, but have to unlearn some bad habits.
Doc, aka Dr. David W. Smith
The Stars Hollow Gazette,