UV
Index: What is it?
Some exposure to sunlight
can be enjoyable; however,
too much could be dangerous.
Overexposure to the sun's
ultraviolet (UV) radiation
can cause immediate effects
such as sunburn and long-term
problems such as skin cancer
and cataracts. The UV Index
is a forecast of the amount
of skin damaging UV radiation
expected to reach the earth's
surface at the time when
the sun is highest in the
sky (solar noon). The amount
of UV radiation reaching
the surface is primarily
related to the elevation
of the sun in the sky,
the amount of ozone in
the stratosphere, and the
amount of clouds present.
The UV Index can range
from 0 (when it is night
time) to 15 or 16 (in the
tropics at high elevations
under clear skies). UV
radiation is greatest when
the sun is highest in the
sky and rapidly decreases
as the sun approaches the
horizon. The higher the
UV Index, the greater the
dose rate of skin damaging
(and eye damaging) UV radiation.
Consequently, the higher
the UV Index, the smaller
the time it takes before
skin damage occurs.
There are two prices
to pay for overexposure
to
UV radiation: a severe
sun burn following
an intense short
term overexposure,
and the more serious
skin
cancers developing
after long term
overexposure.
Melanoma, the more
deadly of the two
types of skin
cancer occurs when
the patient has
been subjected
to several intense
short term overexposures.
Non-melanoma
skin cancers, which
are almost 100%
curable, occur
in people who are overexposed
for very long periods
of time, like construction
workers, farmers, or
fishermen.
Long term overexposure
to UV radiation has
been linked to
the formation
of cataracts in the
eyes as well.
UV Index: How to use it!
As described earlier,
the UV Index is
a forecast
of the probable intensity
of skin damaging ultraviolet
radiation reaching
the surface during
the solar
noon hour (11:30-12:30
local standard time
or 12:30-13:30
local daylight
time). The greater
the UV Index is
the greater
the amount of skin
damaging UV radiation.
How much
UV radiation is needed
to actually damage
one's skin is dependant
on
several factors. But
in general the darker
one's skin is, (that
is the more melanin
one has in his/her
skin)
the longer (or the
more UV radiation)
it takes
to cause erythema (skin
reddening). For those
who always burn and
never tan the times
to burn
are relatively short
compared to those who
almost always tan.
Below are general guidelines
on how to protect oneself
from overexposure to
UV radiation and
the maximum
recommended exposure
time:
| Exposure
Category |
UV
Index |
Maximum
Exposure to Sun |
Protective
Actions |
| Minimal |
0, 1, 2 |
Less than an hour |
Apply skin protection
factor (SPF) 15 sun
screen. |
| Low |
3, 4 |
Less than an hour |
SPF
15 & protective
clothing (hat) |
