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Know More About Sun Protection |
Article by Dr. Seah Pong Pin
Consultant Dermatologist |
What is UVA? |
UVA is a long wavelength ultraviolet ray from the sun.
Ranging from 320 to 400 nanometres in wavelength, UVA rays
are the "aging" rays in the UV spectrum. Some
wavelengths in that range have greater potential to cause
burning than other wavelengths.
Not all sunscreens can protect your skin from UVA rays.
Choose a sunscreen that is broad spectrum (protects skin
from both UVA and UVB rays) or one that specifically stated
on the label that it protect your skin from UVA rays.
Broad-spectrum sunscreens should contain at least one UVA
absorber or physical blocker. UVA absorbers include
avobenzone, oxybenzone or benzophenone. UVA physical
blockers include zinc oxide and titanium dioxide.
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| What
is UVB? |
UVB is a medium wavelength ultraviolet ray from the sun.
Ranging from 280 to 320 nanometres in wavelength, UVB rays
are the "burning" rays in the UV spectrum. Some
wavelengths in that range have greater potential to cause
burning than other wavelengths.
UVB radiation is stronger between late morning and early
afternoon when the sun's rays are directed straight at the
Earth. Sunscreens are capable of protecting the skin from
UVB rays.
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| What
is SPF? |
SPF stands for Sun Protection Factor. It is the ratio of UV
radiation dose required to produce recognizable redness on
skin that has been protected with a sunscreen or fabric, to
UV radiation dose required to produce the same redness on
unprotected skin.
SPF tells you how much longer it will take for your skin to
begin reddening with the product on than if your skin was
unprotected. For example, if you usually start to burn after
10 minutes, using a product with a SPF 15 will increase the
amount of time you can spend in the sun without burning to
150 minutes (15 x 10).
The percentage of burning UV rays that a product blocks does
not increase proportionately with the SPF value. For
example, a SPF 15 blocks about 93% of the burning UV rays
while a SPF 30 blocks about 97%.
It is important to remember that no matter what the SPF,
some UV rays will still reach your skin, and hence no
sunscreen lasts all day. Clouds cannot block UV rays and so
do not think that you are safe from sunburn on a cloudy
day.
Choosing the appropriate level of protection depends on your
skin type and the circumstances of the exposure. Most
dermatologists recommend that you use products with a SPF
between 15 and 30.
Also, remember to reapply sunscreens regularly about every 2
hours.
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| What
is sun protective clothing? |
Sun protective clothing is any garment that provides
adequate protection from the sun. Generally speaking,
clothing should have a SPF value of 15 to 30 or more (blocks
93% to 97% of UV radiation), and cover or shade sufficient
skin to protect a person from the damaging rays of the
sun.
The following are some factors that can affect the sun
protectiveness of clothing:
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- Tightness
of weave or knit
- Fiber
content
- Factory
chemical treatments
- Optical
brighteners in detergent
- Other
laundry treatments
- Garment
style (does not alter SPF values, but garment needs to
cover sufficient skin to be sun protective)
- Sun
protective hats should have at least 3 inch brims all
the way around
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A
study done on the SPF of various fabrics shows that
polyester offered more protection over cotton, wool, rayon,
nylon and linen.
The following table lists the SPF values for various white
fabrics:
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| Type
of Fiber |
Structure |
SPF |
| Polyester |
Plain
woven |
12 |
| |
Double
knit |
32 |
| Cotton |
Plain
woven |
4 |
| |
Jersey
knit |
4 |
| Wool |
Plain
woven |
8 |
| |
Jersey
knit |
22 |
| Rayon |
Plain
woven |
5 |
| Nylon |
Plain
woven |
5 |
| Linen |
Plain
woven |
5 |
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