After
spending last weekend in Vernazza, a small sunny town in the Cinque Terre, I
came back to Siena rather severely sunburned. Parts of my skin glowed painfully
red and any movement or touch was excruciating for a few days after. And you
may be wondering why I didn’t apply more sunscreen to begin with, instead of
trying to find aloe in a nearby farmacia, which entailed explaining my problem
with hand gestures and some revealing of my skin. The problem, or one problem
rather, was that I didn’t feel or see my sunburn until hours after leaving the
seaside. It turns out that this is a normal phenomenon – skin can turn red 2 to
6 hours after the initial burning.
So
some basics: Sunburn is caused by UV radiation from the sun burning the skin. The
ultraviolet radiation from the sun is divided into three categories – A, B, and
C. While the atmosphere, specifically ozone, filters out almost all of the C
subtype along with some A and B, enough UV radiation reach the earth’s surface
to cause burns. The burn will develop for up to 72 hours after the initial exposure
and pain is generally worst 6 to 48 hours after, followed by peeling skin 3 to
8 days afterwards. Additional symptoms of sunburn can include tenderness,
blistering, rash, fever and nausea – these symptoms are caused by the dying
cells releasing toxins and when many cells die, they peel off. In extreme
cases, hospitalization may be necessary for the treatment of sunburn.
Although
all of the immediate effects of sunburn are extremely unpleasant, the worst
problem caused by sunburn is DNA damage. The radiation causes both direct and
indirect DNA damage to skin cells, which can lead to skin cancer. The direct
DNA photo-damage (or damage caused by light) occurs when the UV light excites
the DNA molecule and, within one picosecond, that energy is released. This
energy causes the formation of a bond between two thymine bases, as seen in a
study by Kohler et. al. In the study, researchers created special strands of
DNA with only thymine bases and observed the chemical reaction induced by UV
radiation in which the base pairs dimerise when they are in the right
conformation. Due to the speed of the reaction, even the rapidly moving DNA
molecules appear frozen during the time in which the photo-damage occurs. This
damage impairs the replication process - but don’t worry too much, our cells
are capable of healing themselves up to a certain point. Problems are more
likely to happen when sunburn and DNA damage are frequent; in fact, chronic
damage is believed to be a cause of cancer causing mutations.
A
tan, on the other hand, is the body’s protective response to sun exposure. Skin
cells produce a substance called melanin, which absorbs solar radiation. There
are two types of melanin produced by cells: red pheomelanin and a very dark
brown eumelanin. Both types of melanin cause the darkening of skin color after
sun exposure. UV-A and UV-B radiation cause two different processes in the
development of a tan. First, UV-A radiation causes the oxidation of existing
melanin which causes it darken. In addition, stored melanin is released into
the cell. This mechanism does not increase the amount of melanin in the skin so
there is also no increase in protection against sunburn. The second process,
initiated by UV-B radiation, causes an increased production of melanin, through
the process of melanogenesis. This is a reaction to direct photo-damage, as
discussed previously, and is protective against future UV exposure.
So the major lesson learned: even if you don’t
feel the sunburn happening, wear sunscreen because you’ll probably start
turning a lovely red within the next 6 hours.
Sources:
http://www.chemistrydaily.com/chemistry/Sun_burn
http://researchnews.osu.edu/archive/dnaburn.htm
http://en.wikipedia.org/wiki/Sun_tanning
http://homeremedieshealth.com/home-remedies-for-sunburn/
