This post is an extension of, or a sequel to, or an elaboration on, or an addition to, or . . . oh forget this. Just take a look at what I posted back three years ago (talk about time to think about it), Tan vs. No Tan. Then come back here and read this addendum. Wow! There’s a word worth using more often. Addendum. Addendum. Addendum. Ok. That’s often enough.
Apparently, scientists are now saying that sunscreens cause skin cancer. What?!! And other scientists are saying that caffeine prevents skin cancer. So, I guess, then, not using sunscreens and drinking coffee is all one needs to run off to sun soaked beaches and never again have to worry about skin cancer.
Well, it’s not as easy as all that. But nearly so. Skin color and eye color still tie in. Let’s leave the coffee part for another post. Instead, let’s look at who can tan and who cannot tan. Why? Because scientists actually agree that the more pigment in your skin the more you are protected from the harmful, as well as the beneficial, effects of ultraviolet radiation.
With that controversy out of the way, who gets to play the tanning game?
Albinos (no skin pigment whatsoever) are going to have big, big trouble getting a tan (more than big trouble really – they just can’t do it – not happening – forget even trying). Certain Africans, certain Indians (from India) and certain aboriginal Australians, all with extremely pigmented skin have already reached the ultimate in dark skin and just cannot get any darker. Anywhere in between and the tanning game is still afoot, Watson.
People with blue, green, hazel, or any other light-colored eye irises will also have trouble tanning, but some degree of tanning is still possible. Those with black-colored eye irises have probably also reached the limit of how much further they can darken. As for the rest, those with light brown, brown or dark brown-colored eye irises, again the tanning game is still afoot.
Time of day and year, as well as where, latitudinally, on the planet you live, and what the weather is doing in your part of the world also tie in, but we will not concern ourselves with those criteria at this time.
Instead, let’s find out if tanning is as harmful as some scientists would have us believe.
When someone tells you that sunlight causes DNA damage to the skin and that the resulting tan is a sign of that damage, they are correct. What they do not tell you (either through ignorance or intentional deception) is that the tan protects your skin from 99.9% of the harmful effects of the sun. And that the actual damage is less than 0.1% and produces only a certain degree of sunburn (the intensity of the sunburn depending on the above-mentioned criteria – e.g., skin color, etc.). And the darker you get, the more protection you have.
So let’s take a closer look at the relationship between sunscreens, tanning, and skin cancer. And this can get tricky. So make sure you put on your science caps.
The main characters are (in order of importance):
UVB – Ultraviolet rays that do not age skin, do not tan skin, and float around only during the middle of the day (about 4 to 6 hours), depending on the angle of the sun in your area and at your time of the year. These rays also create Vitamin D and, in excess, cause sunburn.
UVA – Ultraviolet rays that age skin, tan skin, and float around all day long. These rays do not create Vitamin D and do not cause sunburn, but they can cause indirect DNA damage which, unlike a sunburn’s redness and pain, has no warning signs.
Melanin – a photo-protective pigment that absorbs harmful UV-radiation and transforms the energy into harmless heat through a process called “ultra-fast internal conversion.” This enables melanin to dissipate more than 99.9% of the absorbed UF radiation as heat. This prevents the indirect DNA damage that is responsible for the formation of malignant melanoma and other skin cancers.
Melanocytes – melanin-producing cells located in the bottom layer of the skin’s epidermis. There are typically between 1000 and 2000 melanocytes per square millimeter of skin. Melanocytes comprise from 5% to 10% of the cells in the basal layer of epidermis. The difference in skin color between lightly and darkly pigmented individuals is due not to the number (quantity) of melanocytes in their skin but to the melanocytes’ level of activity (quantity and relative amounts of eumelanin and pheomelanin.)
Melanogenesis – a biological process that allows melanocytes to produce melanin. This process leads to a long-lasting tan, in contrast to the tan that originates from oxidation of already-existing melanin.
Direct DNA Damage
Direct DNA damage: The UV-photon is directly absorbed by the DNA (left). One of the possible reactions from the excited state is the formation of a thymine-thymine cyclobutane dimer (right). The direct DNA damage leads to sunburn, causing an increase in melanin production, thereby leading to a long-lasting tan. However, it is responsible for only 8% of all melanoma.
Due to the excellent photochemical properties of DNA, this nature-made molecule is damaged only by a tiny fraction of the absorbed photons. DNA transforms more than 99.9% of the photons into harmless heat. (But the damage from the remaining < 0.1% of the photons is still enough to cause sunburn).
Photoprotection – a group of mechanisms that nature has developed to minimize the damage that the human body suffers when exposed to UV radiation.
Photoprotection of the human skin is achieved by extremely efficient internal conversion of DNA, proteins and melanin. Internal conversion is a photochemical process that converts the energy of the UV photon into small amounts of heat. This small amount of heat is harmless. If the energy of the UV photon were not transformed into heat, then it would lead to the generation of free radicals or other harmful reactive chemical species (e.g. singlet oxygen, or hydroxyl radical).
In DNA this photoprotective mechanism evolved four billion years ago at the dawn of life. The purpose of this extremely efficient photoprotective mechanism is to prevent direct DNA damage and indirect DNA damage. The ultrafast internal conversion of DNA reduces the excited state lifetime of DNA to only a few femtoseconds (10-15s)—this way the excited DNA has not enough time to react with other molecules.
So why do so many scientists now believe sunscreens actually cause cancer? The answer is in the chemicals present in all sunscreens. Apparenlty, these chemicals stimulate free radical formation that actually causes the most severe forms of skin cancers, the malignant melanomas. And that’s not a good thing.
So, what does all this information tell us? Basically, that skin darkening (if done carefully so as to avoid sunburns and free radical formation) is an effective and healthy way to prolong our time in the sun. And that’s probably why mankind has survived the perils of sunlight without the use of sunscreens for so many millennia. Goodbye sunscreens!
[ Above photos: Courtesy of Wikipedia and http://blog.myskin.com/expert/know-your-sunscreen-ingredients ]