Last week, we talked a little about bending of light in light
emitting diodes and about rainbows. The rays of each of the
seven colors violet, indigo, blue, green, yellow, orange and red
are bent in rain drops and reflected back to your eyes at different
angles relative to the direction of the sun”s rays. This reflection
back to your eyes at a different angle for each color of the
rainbow explains why you see the colors spread out in the sky
and why the rainbow is circular. I gather that if you”re high
enough up in a plane and the conditions are just right you can see
a rainbow as a complete circle.
The color of light depends on its wavelength, which increases as
you go from violet to red. The energies of the photons of light
are larger for the shorter wavelengths. This is sort of like the
situation at the beach on a windy day where the waves are higher
and more of them come rolling in. The energy is enough to
erode beaches and knock down buildings in a hurricane. On a
calm day the waves are spaced farther apart, generally are not as
high and carry much less energy. A tsunami is a special case
where a gigantic wave, maybe a hundred feet high, can have
devastating effects. In midocean the tsunami, moving at
hundreds of miles an hour, may just be a foot or two high and not
even be noticed. It”s when it hits shallow water that it rears up its
ugly head.
But I digress. That visible light, those seven colors of our
rainbow, represents only 39 percent of the short-wave radiation
we get from the sun. Some 53 percent of the sun”s radiation is in
the infrared region of the spectrum. This infrared radiation, with
its longer wavelengths, isn”t visible to us but we feel it as heat, a
welcome effect on a raw winter”s day. The other 8 percent or so
of the sun”s output is of growing concern. This is the shorter
wavelength, higher-energy ultraviolet or UV radiation, the
primary cause of skin cancer. I”m a victim of UV, having had a
little chunk taken out of my nose and another from my ear to
remove basal cell carcinomas. For every 10 people who get skin
cancer, 7 will have the least serious basal cell type, two the more
worrisome squamous cell cancer and one will get melanoma, the
most deadly form of skin cancer. This according to Prof. Brian
Diffey of the British National Health Service. (The situation
may be better in the U.S. if we take the figures cited in the FDA
article and attributed to the American Cancer Society. Instead of
10% of skin cancers being melanoma, slightly less than 3% of
the 1.8 million cases diagnosed each year are melanoma, which
causes 79% of the deaths from skin cancer.)
Chastened by my own bits of surgery, I religiously put on a wide
brim Tom Kite type hat and slather on sunscreen before going
out on the golf course. Since I show no significant signs of
sunburn after these outings, I have always felt I was doing a good
job of protecting myself from other skin damage. But I hadn”t
reckoned with the three types of UV we receive from our sun.
Chances are you”ve seen or heard of recent studies questioning
the value of using sunscreens to protect against skin cancer. I
found an informative article on this subject in the July-August
2000 issue of FDA Consumer, the magazine of the U.S. Food
and Drug Administration. Two other interesting sources proved
to be www.sunsmart.com.au and www.ozone.fmi.fi, Australian
and Finnish Web sites, respectively.
There are three regions of the UV spectrum of concern, namely,
UVA, UVB and, of course, UVC. The wavelengths for these are
UVA [400 – 315 nanometers], UVB [315 -280 nanometers] and
UVC [280 -200 nanometers]. These are rather arbitrary
definitions and you might find slightly different wavelengths in
different sources. UVC, with the shortest wavelengths, is the
most energetic, so much so that prolonged exposure would
destroy our skin! But we”re in luck. UVC is absorbed in our
upper atmosphere and doesn”t reach the ground.
So, we”re left with UVA and UVB. Fortunately for all of us, the
amount of UV reaching the ground has been cut down
significantly by the well-known ozone layer. Ozone is a pretty
unstable molecule of three oxygen atoms, compare to the oxygen
gas molecules containing two atoms of oxygen that we breathe.
When a UV photon hits an ozone molecule, the photon is
absorbed and its energy goes into knocking off one oxygen atom,
leaving behind a normal oxygen molecule. The atom that got
knocked off can now either encounter an oxygen molecule to
reform ozone or it can meet up with another free oxygen atom to
form oxygen. Overall, with some seasonal variations, ozone has
been created and destroyed at about the same rate.
At least that was the case until we became hooked on air
conditioning and on aerosols to propel various concoctions such
as hairsprays, shaving cream and the like onto ourselves.
Without going into the chemistry here, we”re all familiar with the
result, a depletion of the ozone and the loss of a significant
portion of our chemical shield against UV. We may be in
reasonably good shape regarding UVB since most of it is
absorbed by sunscreens before reaching the skin. The rub is that
UVA has not been screened out thoroughly in most sunscreens in
the past. I just looked at several more recent sunscreens we have
around the house and all now claim “broad spectrum” protection,
specifically mentioning UVA and UVB.
A big problem is the difficulty in carrying out meaningful studies
of the effect of UVA on the skin. This is painfully evident from
the FDA magazine article and from a lecture by the
aforementioned Prof. Diffey at a conference in Melbourne,
Australia. The lecture is available on the SunSmart Web site.
An obvious problem is the time factor. For example, excessive
sun exposure during childhood may lead to melanoma 20-40
years later. Obviously, trying to retrospectively quantify the
amount and ages of exposure, as well as the recalled usage of
sunscreen, to obtain useful statistics is a daunting task indeed.
Animal studies can only give a crude approximation at best to
human response to exposure, use of sunscreens, etc. Prof. Diffey
cites his own work trying to study the effect of exposure of
human skin to UV. His source of skin is somewhat unusual. He
has friend who is a plastic surgeon who, contrary to what you
might expect, does a lot of breast reduction surgery. He gives
the skin to Prof. Diffey, who then removes the epidermis for his
studies.
Today, the Aussies not only hosted the Olympics but they are
also doing some of the key work in sorting out the skin cancer
problem. For example, in a 5-year study of 1383 adults, workers
at the Queensland Institute for Medical Research in Brisbane that
while sunscreen use resulted in a 40 percent reduction in the risk
of getting squamous cell carcinoma, the rates for basal cell
carcinoma and the much more deadly melanoma were
unchanged. Not an encouraging result! Presumably, it is the
UVB protection that suppresses the squamous cell cancer.
In Australia, the motto is “Slip, Slop and Slap”; slip on a shirt,
slop on the sunscreen and slap on a hat. Apparently, their anti-
skin cancer campaign is working and suntans, especially deep
ones, are going out of style in this athletically oriented society.
As a result, the rates of skin cancer, including melanoma are
going down among the young but not in the older crowd in
which the damage has already been done. There are some who,
like Robin Marks, at the University of Melbourne, break with
those who concentrate on the effects of UVA and UVB. He says
it ”s a matter of sunlight as a whole, not just certain regions of the
spectrum, and his advice is to just keep sunlight off the skin.
And then there”s the SPF, the sun protection factor. I always use
a sunscreen that has an SPF of 30 when I go golfing. My
behavior is probably typical. The FDA magazine cites a study
published in the Journal of the National Cancer Institute in
August of last year. The study found that people using higher
SPF sunscreens tended to stay out in the sun for significantly
longer times than those using lower SPF sunscreens. Prof.
Diffey in his lecture mentioned visiting a pharmacy and looking
over the selection of broad-spectrum SPF30 sunscreens. His
analysis was that just from looking at the ingredients, many were
obviously not providing the same amount of broad-spectrum
protection. So, if you stay out longer you may be getting a lot
more UVA than you thought! Another major complication is
simply the fact that the SPF factors are based on an application
of a uniformly spread dose, say 2 milligrams of sunscreen per
square centimeter. Most people don”t come close to that figure,
let alone apply the sunscreen uniformly over their skin. So, the
actual SPF may be much less or much more than the SPF on the
label, depending on how much and how uniformly you spread
the gunk on your body.
In May 1999, the FDA gave sunscreen manufacturers until May
2001 to comply with newly issued rules. However, new doubts
concerning UVA have led to a delay until December 2002,
hopefully giving the FDA and the industry time to achieve a
better understanding of the effects of and protection against
UVA. In reading the FDA magazine, I”ve gotten a better
appreciation for the difficult nature of the FDA”s job of
evaluating and approving new drugs, hopefully protecting the
public from harm. In this world today we”re bombarded with
conflicting reports about the efficacies of new drugs, alternative
medicines and treatments. It”s quite apparent that, in the case of
sunscreens, the last word has not yet been spoken.
From the standpoint of those who enjoy gazing at the human
body, male or female, the past century”s trend in swimsuits,
culminating in the string bikini, has been quite rewarding. But,
in reality, our ancestors in the vastly less revealing bathing attire
of the late 1800s were probably the smart ones. Obviously, the
long-term play in the stock market now is to buy stock in
bloomers.com. If there is such a site, please don”t take this
advice seriously!…….. I just checked and indeed there is a
bloomers.com. It”s Bloomers Home and Garden Center near
Glassboro, New Jersey. I should have known.
Allen F. Bortrum
