What to Know Before You Choose a Sunscreen

Sunscreen is purchased on the basis of the Sun Protection Factor (SPF) value printed on the label. There is, however, a lot of confusion about how a sunscreen works, how to use it appropriately, and if it should be used at all because it may prevent the production of vitamin D.  This study demonstrates “how sunscreens work, how the SPF is determined, and where the limitations of the current methods exist.” The process of filtering out ultraviolet (UV types A and B) rays of the sun has been studied in laboratories by using computer simulations.

Shorter wavelength rays in the sunlight, namely ultraviolet A and B, are harmful to the skin. UVA can cause sunburns and UVB causes rapid aging of the skin. Sunscreen lotions/sprays block the UV rays from reaching the skin. “The best sunscreen is only as good as the user and can only provide insufficient protection if not applied uniformly, not in the right quantity, or not at all.” The users prefer creams/sprays that are made using a technology that makes the application of the sunscreen easy. Their quality of protection and amount of the UV rays they can block also affects their sale. SPF value is calculated by comparing the smallest amount of UV rays needed to burn the protected skin, with the smallest amount of UV rays needed to burn the unprotected skin.


  • A comparison of the burning impact was made between a sunscreen with SPF 60 and another with SPF 30.
  • Different SPF sunscreens were applied to see how much time was required to produce the same redness of skin, as another tool to compare the SPF values.
  • The laboratory equipment used to mimic the sun shows great variation across the world, owing to the filters used. These were tested in a controlled manner.
  • Initially, laboratory experiments failed to give a clear SPF value due to unstable sunscreens. A more accurate method using computation was therefore developed. These were used to determine the effects of uneven application of the sunscreen and progressively larger amounts were used.


  • The amount of UV rays reaching the skin is more pertinent than the amount that is blocked by the use of sunscreens. It seems trivial that SPF 30 blocks 96.7 percent and SPF 60 blocks 98.3 percent of the UV rays. But, it is significant that SPF 30 allows 3.3 percent rays to reach the skin, while SPF 60 allows only 1.7 percent that is half the burning rays.
  • The sunscreens may block different amounts of UVA and UVB affecting their SPF values. The sunscreens that preferentially block UVB reduce the production of vitamin D, which is essential for our body. However, their uniform protection allows three times more UVB rays to reach the skin, helping in the synthesis of vitamin D.
  • Uneven application of the sunscreen causes valleys in the skin to fill, leaving peaks exposed and covered with less sunscreen. The SPF of the sunscreen depends on these exposed areas. It is observed that the SPF also increases with the amount of sunscreen being applied.

Shortcomings/Next steps
Authors agree that SPF will no longer be the criteria to be used while choosing the sunscreens for the skin. In future, SPF should be given less importance in selecting the sunscreens. The authors suggest that instead the “quality of protection over the whole UVB/UVAII/UVAI range should be the selection criterion.”

Sunscreen that gives protection against both A and B types of UV rays should be selected. The application of the sunscreen should be even and an ample amount should be used. With new technology, the sunscreens will be more robust. They will provide uniform protection and will be independent of the season, time of the day and latitude. Regulations for sunscreens are more stringent in Europe, and the sunscreens made in the Unites States do not have the same UVAPF when tested in Europe. There is no standardized UVA protection, but authors recommend buying sunscreens with high values for Ecamsule and zinc oxide. The sunscreens blocking a wide range (broad spectrum) of UV rays will soon become available.

For More Information:
Sun Protection Factors: Worldwide Confusion
British Journal of Dermatology, 2009
By U. Osterwalder; B. Herzog
From the Ciba Inc., Basel, Switzerland

*FYI Living Lab Reports Are Summaries of the Original Research.

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