Most people today are aware of at least some of the damaging
effects that sunlight has on the skin. In addition to painful
sunburns, excessive exposure to sunlight can cause sun damage
that prematurely ages the skin, causes blemishes, and greatly
increases the risk of various types of skin cancer. Unfortunately,
although we know protecting uncovered skin is important, with a
large variety of sunscreens, sunblocks, lotions, gels, sprays, mists,
and sticks marketed in different strengths and for different
purposes, it can be difficult to determine how to best protect
yourself.
The Sun’s Damaging Rays
When it comes to avoiding sunburn and sun damage, the forms of
sunlight we’re most concerned with are invisible waves of
ultraviolet light classified as UVA and UVB. UVA and UVB pass
through air to the Earth’s surface, and they can even pass through
clouds, which is why you can sunburn on a cloudy day.
Approximately 95% of the ultraviolet light that penetrates your skin
is UVA. This form is responsible for tanning, penetrates more
deeply than UVB, and is an important factor in causing sun
damage and skin cancers. UVB accounts for about 5% of the UV
light that strikes your skin. Although UVB doesn’t penetrate as
deeply as UVA, it has more energy and is the primary cause of
sunburn. Most sunscreens protect against UVB, and fewer protect
against both UVA and UVB. The sun protection factor (SPF) rating
is a general measure of how well a sunscreen protects against
developing a sunburn from UVB.
SPF
SPF measures the time it takes to produce a sunburn reaction on
protected skin compared to unprotected skin. However, avoid
believing you can stay in the sun 10 times longer with SPF 10
sunscreen, because there are misconceptions about SPF and
sunscreen. SPF only measures protection against UVB, and does
not measure UVA protection. Also, an SPF 30 sunscreen is not
twice as effective as SPF 15. An SPF 15 sunscreen blocks around
93% of UVB; whereas an SPF 30 sunscreen blocks about 97%. In
addition, people generally apply sunscreen more thinly than
recommended, which lowers the SPF. Sunscreens claiming to be
water-resistant will wash off after about 40 minutes and those
claiming to be very water-resistant protect for up to 80 minutes.
Certain labels such as waterproof, sunblock, and all-day protection
are misleading, and governmental agencies in various parts of the
world have recommended banning their use on sunscreen bottles
for this reason.
Types of Sunscreen and How They Work
Sunscreens can be classified by how they protect against UV light
as well as by the type of UV protection they provide. Sunscreens
protect against UV damage by either chemical or physical means,
or a combination of both. Chemical sunscreens are absorbed into
the skin and are designed to halt UV before it damages skin. When
UV light strikes the sunscreen molecules, absorbed energy excites
the molecules, which release the energy as heat as they return to
their former state. Conversely, physical sunscreens act as a
protective film on the surface of the skin. UV light that strikes the
sunscreen molecules is either absorbed into the sunscreen, or it is
scattered and reflected away before passing into the skin. Most
sunscreens protect against UVB, but fewer are what are known as
broad-spectrum or full-spectrum sunscreens, which protect against
both UVA and UVB. Whether a sunscreen blocks against UVB
alone or both UVA and UVB depends on its ingredients.
Sunscreen Ingredients
One of the first ingredients used in modern sunscreens was paraaminobenzoic
acid, or PABA. Although PABA protects against
UVB, it produces adverse reactions in some people, which is why
you will sometimes see PABA-free listed on sunscreen bottles.
Today cinnamates are the most frequently used sunscreen
ingredient for UVB protection. Two increasingly common UVA
protectants are avobenzone and ecamsule. Among physical
sunscreen ingredients, metallic compounds such as zinc oxide or
titanium dioxide are common and protect against UVA and UVB.
These metallic, physical sunscreen ingredients are also sometimes
blended into chemical sunscreens along with the other chemical
ingredients.
The Sunscreen Controversy
There is some controversy over sunscreen use. You produce
vitamin D as a result of UV exposure, and some people are
concerned that sunscreen use may cause a deficiency. However,
people have been found to maintain normal vitamin D levels with
proper sunscreen use, and those with a deficiency or minimal sun
exposure can obtain additional vitamin D in supplements. Another
concern stems from an observation that since sunscreen protects
from the UVB rays that cause sunburn, people stay in the sun
longer, potentially increasing the chance of developing melanoma
skin cancers from UVA exposure. To reduce this risk, use a
sunscreen with UVA protection.
Proper Sunscreen Application and Use
Dermatologists recommend using a broad-spectrum sunscreen of
SPF 15 or greater. Apply the amount recommended on the
sunscreen bottle fifteen to thirty minutes before sun exposure.
Shake the bottle well and remember to apply sunscreen to
frequently forgotten areas such as the ears, back of the neck,
bridge of the nose, scalp, hands, and feet. Reapply sunscreen
every two hours or when done toweling off after swimming.
Sunscreen is just one way to protect yourself from the sun. In
addition, try to avoid sun exposure between the hours of 10:00
A.M. and 2:00 P.M. when the sun is most intense. When possible,
wear long sleeved shirts and pants, and wear a wide-brimmed hat
to protect your head and neck. Infants under 6 months of age have
particularly thin, sensitive skin and should be shielded from the
sun. Since children often receive much more sun exposure than
adults but tend to dislike sunscreen, a variety of physical
sunscreens now come in exciting colors and packaging to make
them more appealing.
Choosing the Right Sunscreen
Always opt for a broad spectrum sunscreen that protects against
both UVA and UVB. Physical sunscreens generally offer the best
sun protection, but they are often visible on the skin. As a remedy,
some sunscreens reduce the size of the zinc oxide and titanium
dioxide ingredients to avoid visible residues. Determining the
correct SPF to use depends on how susceptible you are to burning
and the amount of time you plan to spend in the sun. The
effectiveness of your sunscreen will depend both on how well you
apply it and the protective ingredients in the sunscreen. If you find
that your skin is sensitive to a specific ingredient or sunscreen
additive, or if you don’t like the way the sunscreen feels on your
skin, you can use what you now know about sunscreens to find a
different formulation that will suit your needs.
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