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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.

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.

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.

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:

  • 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
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:


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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