06 August 2008

SPF stands for Sun Protection Factor.The SPF number on the product's label refers to the strength of protection, and the length of time a sun-screening product will allow your skin to be in the sun without burning - relative to the length of time bare skin (or skin without the product applied) would burn or redden. The higher the SPF number, the longer the period of protection against the sun.

Your skin has a natural SPF, partially determined by how much melanin you have, or how darkly pigmented your skin is. The SPF is a multiplication factor.
For instance, if you normally burn after 10 minutes without wearing a sunscreen, a sunscreen with an SPF of 15 will protect you for 150 minutes (2.5 hours).
Here’s the formula for calculating : 10 minutes x 15 SPF = 150 minutes (2.5 hours).

SunlightAlthough the SPF only applies to UV-B, the labels of most products indicate if they offer broad spectrum protection, which is some indication of whether or not they work against UV-A radiation. The particles in sunblock reflect both UV-A and UV-B.

What you need to know about SPF?
  1. There are two systems for specifying a sunscreen's protection. American SPF numbers are double the SPF numbers on European products. An American SPF 30 sunscreen is the same as SPF 15 in Europe. Check which system is being used when you buy, and ask if you are in doubt.
  2. SPF is a laboratory measure of effectiveness. The European SPF system is based on the time a person with pale skin can remain in the sun without getting red and tender. This is usually 20 minutes in spring.
  3. If an SPF 8 sunscreen was applied, this would mean you could stay out in the spring sun for 8 x 20 minutes (160 minutes) without getting burnt.
  4. In practice, we don't know how quickly we burn, while factors such as sweat, water and application reduce sunscreen's effectiveness, so you shouldn't try to use this calculation as a guide.

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