More Dangerous Than You Expect: the Sun’s Rays
More Dangerous Than You Expect: the Sun’s Rays
  • Cho Ku Yun-ji 기자
  • 승인 2008.06.08 01:21
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The weather is getting hotter and the season of strong sunlight has arrived.  It is well-known that the sun’s rays should be avoided, not only because they tan the skin but because they have a harmful effect on skin, which leads to skin cancer in the worst cases.  Then, what methods are advisable for people who want to avoid the sun’s harm?  The Sookmyung Times is ready to quench your curiosity about sunscreen and hot summer sunshine.

What is SPF in Sunscreen?

According to the MedTerms Dictionary, SPF stands for Sun Protection Factor, which is a number on a scale for rating sunscreens.  SPF numbers on a package can range from as low as 2 to as high as 60.  These numbers refer to the product's ability to screen or block out the sun's burning rays.  The SPF rating is calculated by comparing the amount of time needed to produce sunburn on protected skin to the amount of time needed to cause sunburn on unprotected skin.  Let us take, for instance a fair-skinned person who would normally turn red after ten minutes in the sun.  Ten minutes is their ‘initial burning time.’  If that person uses a sunscreen with SPF two, it takes 20 minutes in the sun for that person's skin to turn red.  Now, if that person uses a sunscreen with SPF 15, it multiplies the initial burning time by 15, so it takes 150 minutes, or two and half hours, for that person's skin to turn red.  Sunscreens with an SPF of 15 or higher are generally thought to provide useful protection from the sun's harmful rays.  (

How Does the Ultraviolet Light Affect Skin?

The sun's rays contain different wavelengths of ultraviolet (UV) light.  The two types of UV rays that pass through the earth's atmosphere and cause damage to the skin are UVB and UVA.  UVB rays are the primary cause of sunburn and affect the outer layer of skin.  The strength of UVB radiation depends upon the time of day, season of the year, and geographic location.  UVB rays are most intense from 10 am to 2 pm and are stronger in summer, at higher altitudes, and closer to the equator.  Unlike UVB rays, which do not penetrate glass, UVA rays can travel through window glass and damage the deeper layers of the skin.  Both UVA and UVB light contribute to age-related changes in the skin such as wrinkles, freckles, age spots, and prominent blood vessels.  Both UVA and UVB exposure raise the risk of skin cancer. 

Sunscreens can be broadly classified into two categories: chemical sunscreens and physical sunscreens.  Chemical sunscreens absorb UV radiation while physical sunscreens act by physically blocking it.  Chemical sunscreens can be UVA or UVB absorbers.  Many sunscreens have a combination of ingredients and may contain both physical and chemical sunscreens.  Physical sunscreens are good blockers of both UVA and UVB radiation.  The two most common physical blockers of UV radiation are titanium dioxide and zinc oxide.

The following are examples of chemical ingredients used in sunscreens: 
PABA (para-aminobenzoic acid):
Rarely found in modern preparations, PABA  was an early chemical sunscreen that often induced sensitivity reactions. 
PABA esters (glyceryl, padimate A and padimate O): These newer preparations  have fewer side effects than the original PABA. 
Salicylates (homosalate, octyl salicylate) 
Cinnamates (cinoxate, octyl methoxycinnamate or octocrylene):
Octocylene is a  cinnamate with both UVA- and UVB-absorbing properties. 
Benzophenones: These can absorb both UVA and UVB rays.

Are There Any Differences among Rays of Sunlight?

Ultraviolet light is classified into three groups; UV A, B, and C.  Ultraviolet C is known as the worst one among three in that it can harm life on earth, but fortunately, the ozone layer protects us from these rays.  On the other hand, ultraviolet A and B do penetrate the ozone layer and affect people’s skin.  According to MedTerms Dictionary, scientists long blamed ultraviolet B as the sole culprit in causing skin cancer in persons with a history of sunburn and repeated overexposure to ultraviolet radiation, because ultraviolet A is weaker than ultraviolet B.  Recent studies, however, have implicated ultraviolet A as a possible cause of skin cancer.  In addition to natural light from the sun, artificial light from tanning lamps contains ultraviolet A and ultraviolet B.  In spite of their harmfulness, they can also maintain or improve health.  When ultraviolet light strikes human skin, it triggers the production of vitamin D, which promotes the growth of bones and teeth.

According to recent studies, it is becoming increasingly important to protect yourself from UVB and UVA.  Dr. Gary Halliday, the Professor of Dermatology, University of Sydney, said, “Our studies indicate that it is important to protect from both UVB and UVA.  Therefore the best advice is to avoid sunlight exposure as much as possible and, if this is not possible, use a sunscreen which protects from both of them.”

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