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Sun avoidance and regular sunscreen use
are widely promoted by organizations and individuals interested
in skin cancer prevention. However, 70% of those who participated
in a beach survey were on the beach to get or to maintain
a suntan. Although they stayed on the beach for an average
of 4 hours, only half were using sunscreen.
On the mountains, and despite past sunburn
experience, skiers often do not use sunblock. A springtime
survey of skiers in Alberta showed that only two-thirds were
using sunscreen, and of those using a sunscreen, one third
were sunburned at the time of survey.
There appears to be some confusion about
the messages people are getting about sunblock and why they're
so important. Some use sunscreens to prevent sunburn, whereas
others use sunscreens to improve sun tanning. Some wish to
avoid the wrinkling associated with sun exposure, and others
believe that sunscreens prevent all types of skin cancer.
Yet others seem to believe that they can use sunscreens in
order to prolong their time in the sun.
- Prevents sun burns
- Prevents photodamaged skin (aged look
- brown spots, wrinkles)
- Prevents actinic keratosis and perhaps
squamous cell cancers
- May prevent other skin cancers
A sunburn is caused by exposing your
skin to too much ultraviolet (UV) light from the sun, that
is, lightwaves that measure approximately 200-400nm.
UV light can be broken down into 4 component parts that include:
- ultraviolet A1 (UVA1), 340-400nm
- ultraviolet A2 (UVA2), 320-340nm
- ultraviolet B (UVB), 290-320nm
- ultraviolet C (UVC), 200-290nm
There are two major types of UV sun damage:
UVA-type damage, with light wavelengths of 340-400nm, and
UVC-type damage, which includes light wavelengths of up to
340nm. UVA-type damage can cause the skin to tan and may cause
very weak burns, while UVC-type damage causes skin to burn.
The average user of sunscreen tends
to use significantly less sunscreen than the amount required
to achieve the SPF listed on the container.
Many experts recommend that frequent
application during sun exposure is required. However, a group
of children were tested by spreading on 1 application of sunscreen
to one side of their bodies, and four applications to the
other.
They then spent 6 hours in the sun. One
application provided the same level of protection as four
applications, confirming the adequacy of a single daily application
of a sunscreen in that situation.
As molecules of sunscreen are present
in their active state in the sunscreen, sunscreens work immediately
upon application. The only reason for application early is
to allow absorption into the skin so that the sunscreen is
less likely to be washed off, should the person be entering
the water. Even so, modern sunscreens are quite resistant
to removal from the skin.
SPF is the ratio of the minimal ultraviolet
dose required to produce redness with and without a sunscreen.
For example, if it took ½ hour for your skin to become
sunburned without any sunscreen, then for a sunscreen that
has a 15 SPF rating, you could stay in the sun for 15 times
longer (or 7.5 hours) before you get sunburned. This is provided,
of course, that you've applied the sunscreen properly so that
you're getting the prescribed protection.
Sunscreens can be both an irritant
and an allergen, though allergic reactions are rare. Irritant
reactions, however, abound. One classic error in sunscreen
application is to put a large amount of sunscreen on the forehead.
Perspiration and gravity can cause the sunscreen to migrate
down your forehead into your eyes, causing a stinging sensation.
Some people attribute this to an allergic reaction and discontinue
use. It's also important to wash your hands after applying
sunscreen, since rubbing your sunscreen covered finger near
your eyes can induce an irritant reaction.
It appears that a great deal of time
can elapse between actual sun damage and the development of
skin cancer or other skin problems like photoaging. Therefore,
it is important to protect your skin from an early age when
you are out in the sun.
Many elderly people can become quite
obsessed by sun avoidance, and their quality of life can suffer.
Sometimes, if they are diagnosed with an actinic keratosis
or basal cell carcinoma, they can become anxious and almost
leap from shadow to shadow. However, few of them are likely
to develop new skin cancers from present sun exposure. As
long as they are prudent about avoiding excessive sun exposure
and protecting their skin to prevent sunburn, they can continue
to enjoy time outdoors.
There is clear evidence that sunscreens
are helpful in preventing actinic keratoses, which are warty
lesions that can occur on sun-exposed skin of the face or
hands. Research has shown that these lesions can develop into
a cancer called squamous cell carcinoma, and that this is
linked to a cumulative exposure to the sun.
However, there is surprisingly little
evidence that sunscreens have much effect in preventing another
kind of skin cancer called basal cell carcinoma, or for malignant
melanoma. For malignant melanoma and for basal cell carcinoma,
the character and timing, that is, the type of sunlight and
your age at the time of the exposure to the sun appears to
be more important than the cumulative dose.
Adapted from an article by David I.
McLean, MD, and Richard Gallagher, MA
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